Polyamide resin composition, multilayer container and method for producing recycled polyester

Abstract

To provide a polyamide resin composition which, when used for a product such as a container containing a polyester, is excellent in color tone of the product and is also excellent in color tone of a recovered polyester obtained by recycling the product.SOLUTION: There is provided a polyamide resin composition which comprises a polyamide resin (Y), a yellowing inhibitor (A) and a color tone adjusting agent (B), wherein the solubility (Sa) of the yellowing inhibitor (A) in a 1.0% aqueous solution of sodium hydroxide is smaller than the solubility (Sb) of color tone adjusting agent (B) in a 1.0% aqueous solution of sodium hydroxide and the difference in the solubility [(Sb)-(Sa)] is 100 mg / L or more.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a polyamide resin composition, a multilayer container, and a method for producing recycled polyester. [Background technology]

[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, these properties 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 resins with 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, polyester resin compositions containing polyamides are more susceptible to yellowing due to heat history than polyester alone. Therefore, yellowing occurs particularly during the recycling process in which containers are recovered and the resin is reused. Because this reduces the commercial value of packaging containers, efforts are being made to suppress yellowing. For example, Patent Document 1 discloses a multilayer container having a polyester resin composition layer containing a polyester resin and an amino group-containing compound having yellowing suppression ability, and a polyamide resin layer containing a polyamide resin, and a method for producing recycled polyester. Furthermore, Patent Document 2 discloses a resin composition containing a polyester resin recycled from polyester resin molded products, a resin other than polyester, and a specific amount of pigment, for the purpose of improving the transparency of recycled PET due to yellowing and improving moldability, heat resistance, and strength and elongation properties. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] International Publication No. 2017 / 057463 [Patent Document 2] Japanese Patent Application Laid-Open No. 2004-359914 Summary of the Invention [Problem to be solved by the invention]

[0006] As mentioned above, polyester resin containers containing polyamide tend to yellow easily, and the recycled polyester obtained by recycling these containers also tends to have a yellowish tinge. As a method for counteracting the yellow color, for example, as described in Patent Document 2, it is conceivable to add a colorant such as a blue pigment, which is the opposite (complementary) color. In order to reduce the yellow color, it is necessary to add a colorant to the container made from recycled polyester to suppress yellowing. However, this makes the blue color more noticeable, making the container less colorless and reducing the freedom of design of the container. Therefore, there has been a demand for a polyamide resin that can be used in polyester-containing containers and the like, that can produce recycled polyester in which the yellow color is effectively neutralized, and that can produce containers and the like with little blue color. Therefore, an object of the present invention is to provide a polyamide resin composition that, when used in products such as polyester-containing containers, gives the products excellent color tone, and further, gives the recovered polyester obtained by recycling the products excellent color tone. [Means for solving the problem]

[0007] As a result of intensive research in view of the above-mentioned problems, the present inventors have found that a polyamide resin composition containing a yellowing inhibitor and a color tone adjuster having a specific solubility relationship can solve the above-mentioned problems, and have thus completed the present invention. The present invention provides the following [1] to

[14] .

[0008] [1] A polyamide resin composition comprising a polyamide resin (Y), a yellowing inhibitor (A), and a color tone adjuster (B), wherein the solubility (Sa) of the yellowing inhibitor (A) in a 1.0% aqueous sodium hydroxide solution is smaller than the solubility (Sb) of the color tone adjuster (B) in a 1.0% aqueous sodium hydroxide solution, and the difference in solubility [(Sb) - (Sa)] is 100 mg / L or more. [2] Color tone adjuster (B) is the color b of a polyamide resin containing 10 ppm of color tone adjuster (B). * The polyamide resin composition according to [1] above, wherein the color tone adjuster is a color tone adjuster having a value greater than 0. [3] The polyamide resin composition according to [1] or [2] above, wherein the solubility (Sa) of the yellowing inhibitor (A) in a 1.0% aqueous sodium hydroxide solution is 100 mg / L or less. [4] The polyamide resin composition according to any one of the above [1] to [3], wherein the yellowing inhibitor (A) is an anthraquinone dye. [5] The polyamide resin composition according to any one of [1] to [4] above, wherein the color tone adjuster (B) is at least one selected from the group consisting of vitamin B compounds and quinophthalone compounds. [6] The polyamide resin composition according to any one of the above [1] to [5], wherein the content of the yellowing inhibitor (A) is 100 to 1500 ppm based on the total amount of the polyamide resin composition. [7] The polyamide resin composition according to any one of the above [1] to [6], wherein the content of the color tone adjuster (B) is 10 to 6000 ppm based on the total content of the polyamide resin composition. [8] The polyamide resin composition according to any one of [1] to [7] 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. [9] A multilayer container having a polyester layer containing a polyester resin (X) and a polyamide layer containing the polyamide resin composition according to any one of [1] to [8] above.

[10] The multilayer container according to the above [9], wherein the content of the polyamide resin composition is 0.05 to 7.0% by mass based on the total amount of all polyamide layers and all polyester layers.

[11] The multilayer container according to [9] or

[10] , 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.

[12] The multilayer container according to any one of [9] to

[11] above, which is a multilayer hollow container.

[13] The multilayer container according to any one of [9] to

[12] above, which has a 3 to 5 layer structure, and the outermost layer and the innermost layer are polyester layers.

[14] A method for producing recycled polyester, comprising the step of washing the multilayer container or its pulverized product with an alkaline aqueous solution to recover the polyester. [Effects of the Invention]

[0009] According to the present invention, it is possible to provide a polyamide resin composition that has excellent color tone when used in polyester-containing containers and the like, and that also has excellent color tone when used in recovered polyester obtained by recycling such containers and the like. DETAILED DESCRIPTION OF THE INVENTION

[0010] [Polyamide resin composition] The polyamide resin composition of the present invention comprises a polyamide resin (Y), a yellowing inhibitor (A), and a color tone adjuster (B), wherein the solubility (Sa) of the yellowing inhibitor (A) in a 1.0% aqueous sodium hydroxide solution is smaller than the solubility (Sb) of the color tone adjuster (B) in a 1.0% aqueous sodium hydroxide solution, and the difference in solubility [(Sb) - (Sa)] is 100 mg / L or more. By using the polyamide resin composition of the present invention in a container or the like containing a polyester, the color tone of the container or the like is excellent, and furthermore, the color tone of the recovered polyester obtained by recycling the container or the like is also excellent.

[0011] <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.

[0012] The xylylene group-containing polyamide resin is obtained by polycondensation of a diamine containing xylylene diamine with a dicarboxylic acid, and has constitutional units derived from xylylene diamine and constitutional 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 still more preferably 90 to 100 mol % of constitutional units derived from xylylene diamine among constitutional units derived from diamine (diamine units). The xylylenediamine is preferably meta-xylylenediamine, para-xylylenediamine, or both, with meta-xylylenediamine being more preferred. The diamine units constituting the xylylene group-containing polyamide resin preferably contain meta-xylylenediamine-derived structural units at 50 mol % or more, more preferably at 70 mol % or more, even more preferably at 80 to 100 mol %, and even more preferably at 90 to 100 mol %. When the meta-xylylenediamine-derived structural units in the diamine units are within the above range, the polyamide resin has better gas barrier properties.

[0013] 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 ethylenediamine, tetramethylenediamine, pentamethylenediamine, 2-methylpentanediamine, hexamethylenediamine, heptamethylenediamine, octamethylenediamine, nonamethylenediamine, decamethylenediamine, dodecamethylenediamine, 2,2,4-trimethyl-hexamethylenediamine, and 2,4,4-trimethyl-hexamethylenediamine; 1,3-bis(amino)-2-(2-methyl-2-methyl-1,2-diamine); alicyclic diamines such as 1,4-bis(aminomethyl)cyclohexane, 1,4-bis(aminomethyl)cyclohexane, 1,3-diaminocyclohexane, 1,4-diaminocyclohexane, bis(4-aminocyclohexyl)methane, 2,2-bis(4-aminocyclohexyl)propane, bis(aminomethyl)decalin, and bis(aminomethyl)tricyclodecane; and diamines having an aromatic ring such as bis(4-aminophenyl)ether, paraphenylenediamine, and bis(aminomethyl)naphthalene.

[0014] 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).

[0015] That is, the polyamide resin (Y) preferably has structural units derived from a diamine containing 50 mol% or more of structural units derived from xylylenediamine and structural units derived from a dicarboxylic acid containing 50 mol% or more of structural units derived from adipic acid, more preferably 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, and even more preferably has structural units derived from a diamine containing 90 mol% or more of structural units derived from xylylenediamine and structural units derived from a dicarboxylic acid containing 90 mol% or more of structural units derived from adipic acid. As the xylylenediamine, metaxylylenediamine is preferred. Furthermore, the remaining dicarboxylic acid units excluding adipic acid are preferably structural units derived from an α,ω-straight-chain aliphatic dicarboxylic acid having 4 to 20 carbon atoms.

[0016] Another preferred example of a xylylene group-containing polyamide resin is a polyamide resin in which 70 mol % or more of the diamine units are structural units derived from xylylene diamine (preferably meta-xylylene diamine), 70 to 99 mol % of the dicarboxylic acid units are structural units derived from adipic acid, and 1 to 30 mol % are structural units derived from isophthalic acid. The polyamide resin is preferably a polyamide resin in which 80 mol % or more of the diamine units are structural units derived from xylylene diamine (preferably meta-xylylene diamine), 80 to 99 mol % of the dicarboxylic acid units are structural units derived from adipic acid, and 1 to 20 mol % are structural units derived from isophthalic acid, and more preferably a polyamide resin in which 90 mol % or more of the diamine units are structural units derived from xylylene diamine (preferably meta-xylylene diamine), 80 to 99 mol % of the dicarboxylic acid units are structural units derived from adipic acid, and 1 to 20 mol % are structural units 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.

[0017] 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.

[0018] 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, they are preferably produced by a method in which a nylon salt composed of a diamine and a dicarboxylic acid is heated under pressure in the presence of water and polymerized in a molten state while removing the water. Alternatively, they may be produced by a method in which the diamine is 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 raise the reaction temperature so that it does not fall below the melting points of the resulting oligoamide and polyamide, while the 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.

[0019] The xylylene group-containing polyamide resin is preferably polycondensed in the presence of a phosphorus atom-containing compound, which improves processing stability during melt molding and makes it easier to suppress coloration. As the phosphorus atom-containing compound, a hypophosphorous acid compound and a phosphorous acid compound are preferred, and a hypophosphorous acid compound is more preferred. The phosphorus atom-containing compound is preferably an organic metal salt, and more preferably an alkali metal salt.

[0020] Examples of the hypophosphorous acid compound include hypophosphorous acid, metal hypophosphites, metal phenylphosphonite, ethyl hypophosphite, dimethylphosphinic acid, phenylmethylphosphinic acid, phenylphosphonite, and ethyl phenylphosphonite, from the viewpoint of promoting the polymerization reaction and preventing discoloration, and metal hypophosphites are preferred. Examples of metal hypophosphite include sodium hypophosphite, potassium hypophosphite, lithium hypophosphite, and calcium hypophosphite, with sodium hypophosphite being more preferred. Examples of metal phenylphosphonite salts include sodium phenylphosphonite, potassium phenylphosphonite, and lithium phenylphosphonite.

[0021] Examples of the phosphorous compound include phosphorous acid, pyrophosphorous acid, metal phosphites, 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 the metal ethylphosphonate include sodium ethylphosphonate and potassium ethylphosphonate. Examples of the metal phenylphosphonate include sodium phenylphosphonate, potassium phenylphosphonate, and lithium phenylphosphonate. The phosphorus atom-containing compound may be used alone or in combination of two or more kinds.

[0022] The 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. If a large amount of the phosphorus atom-containing compound is used, the polyamide resin may gel. Therefore, from the viewpoint of adjusting 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, such as lithium hydroxide, sodium hydroxide, potassium hydroxide, rubidium hydroxide, and cesium hydroxide, and 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 a polyamide resin, the amount of the 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, from the viewpoint of suppressing gel formation.

[0023] The number average molecular weight of the polyamide resin is appropriately selected depending on the application and molding method of the multilayer container, but from the viewpoint of moldability and strength of the multilayer container, it is preferably 10,000 to 60,000, more preferably 11,000 to 50,000. The number average molecular weight of the polyamide resin is calculated from the following formula (2). Number average molecular weight=2×1,000,000 / ([COOH]+[NH2])...(2) (In the formula, [COOH] represents the concentration (μmol / g) of terminal carboxyl groups in the polyamide resin, and [NH2] represents the concentration (μmol / g) of terminal amino groups in the polyamide resin.) The terminal carboxyl group concentration is determined by neutralizing a solution of polyamide in benzyl alcohol with an aqueous sodium hydroxide solution and calculating the concentration.

[0024] In the present invention, 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, still more preferably 30 μmol / g or less, and even more preferably 20 μmol / g or less, from the viewpoint of suppressing yellowing of the recycled polyester. The terminal amino group concentration of polyamide resin (Y) can be determined by precisely weighing the polyamide resin, dissolving it in a phenol / ethanol = 4 / 1 volumetric solution with stirring at 20 to 30°C, and after complete dissolution, rinsing the inner wall of the container with 5 mL of methanol while stirring, and neutralizing titrating it with 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 diamine and dicarboxylic acid, a method of carrying out a polycondensation reaction by charging a monocarboxylic acid that caps the amino group together with the diamine and 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.

[0025] <Yellowing inhibitor (A)> The polyamide resin composition of the present invention contains a yellowing inhibitor (A), and the solubility (Sa) of the yellowing inhibitor (A) in a 1.0% aqueous sodium hydroxide solution is smaller than the solubility (Sb) of the color tone adjuster (B) described below in a 1.0% aqueous sodium hydroxide solution, and the difference in solubility [(Sb) - (Sa)] is 100 mg / L or more. From the viewpoint of effectively improving the color tone of both the product such as the container and the recycled polyester, the content of the yellowing inhibitor (A) is preferably 1 to 2400 ppm, more preferably 10 to 2000 ppm, even more preferably 100 to 1500 ppm, still more preferably 200 to 1500 ppm, still more preferably 200 to 700 ppm, and still more preferably 300 to 700 ppm, relative to the entire polyamide resin composition. In the present invention, "ppm" means parts per million by mass.

[0026] The solubility (Sa) of the yellowing inhibitor (A) in a 1.0% aqueous sodium hydroxide solution is preferably 100 mg / L or less, more preferably 10 mg / L or less, even more preferably less than 10 mg / L, and even more preferably, the yellowing inhibitor (A) is insoluble in a 1.0% aqueous sodium hydroxide solution. In this specification, "insoluble" means that the solubility is less than 10 mg / L, meaning that the solubility is so low that it cannot be practically measured. When the yellowing inhibitor (A) has a solubility in a 1.0% aqueous sodium hydroxide solution within the above range, the product color tone when used in a product such as a polyester-containing container is excellent, and further, the color tone of the recovered polyester obtained by recycling the product is also excellent. In the present invention, "1.0% aqueous sodium hydroxide solution" refers to an aqueous solution obtained by dissolving 10 g of sodium hydroxide in 1 L of water at 25°C. Furthermore, in the present invention, "solubility" refers to the solubility at 25°C.

[0027] The yellowing inhibitor (A) is preferably a dye, more preferably a blue dye or a purple dye, and preferably a blue dye. By using a dye, the transparency of products such as containers can be maintained, and recycled polyester with excellent transparency can be obtained. The color tone of the yellowing inhibitor (A) can be confirmed by incorporating it into a polyamide resin. For example, the color tone of the yellowing inhibitor (A) can be measured using a polyamide resin (polyxylylene adipamide) containing 10 ppm of the yellowing inhibitor (A). Color b of polyamide resin containing 10 ppm of yellowing inhibitor (A) * is preferably smaller than 0, more preferably not less than -30 and less than -1, and even more preferably not less than -15 and less than -2. The chromaticity of the polyamide resin containing 10 ppm of the yellowing inhibitor (A) can be obtained by measuring a 3 mm thick plate of polyxylylene adipamide containing 10 ppm of the yellowing inhibitor (A) with a colorimeter. Specifically, the same method as used to evaluate the recycled polyester in the Examples can be used. When the chromaticity is within the above range, the polyamide resin composition can be used in products such as polyester containers, resulting in excellent color tone, and the recovered polyester obtained by recycling the product can also have excellent color tone.

[0028] Dyes that can be used as the yellowing inhibitor (A) include anthraquinone dyes, pyrazolone dyes, coumarin dyes, perinone dyes, methine dyes, and quinophthalone dyes, and the yellowing inhibitor (A) is preferably an anthraquinone dye. Examples of the anthraquinone dye include anthraquinone dyes in which a hydrogen atom on an aromatic ring is substituted with an aromatic amine, an aliphatic amine, a hydroxyl group, or a halogen, and anthraquinone dyes in which a hydrogen atom on an aromatic ring is substituted with an aromatic amine are preferred. By using an anthraquinone dye, even a very small amount can suppress yellowing of recycled polyester obtained from containers and the like. The anthraquinone dye is more preferably an anthraquinone blue dye. The anthraquinone dye is preferably a compound represented by the following formula (1).

[0029] [ka] (In the formula, n represents the number of R, and two n's each independently represent 1 to 5. Each R independently represents an alkyl group having 1 to 4 carbon atoms. Each two X's independently represent a hydrogen atom or a hydroxyl group.)

[0030] In formula (1), n ​​is 1 to 5, preferably 2 to 5, and more preferably 2 to 3. By setting n within the above range, yellowing of the recycled polyester can be suppressed. Each R independently represents an alkyl group having 1 to 4 carbon atoms, and is preferably at least one selected from the group consisting of a methyl group and an ethyl group. R preferably substitutes at least at the para-position or ortho-position relative to the amino group, more preferably at least at the ortho-position, and even more preferably at the ortho- and para-positions. Each of two X independently represents a hydrogen atom or a hydroxyl group, and preferably a hydrogen atom. Specific examples of the compound represented by formula (1) include 1,4-bis[(2-ethyl-6-methylphenyl)amino]anthraquinone, Solvent Blue 97, Solvent Blue 104, Solvent Green 3, and Solvent Green 28, and 1,4-bis[(2-ethyl-6-methylphenyl)amino]anthraquinone, Solvent Blue 97, and Solvent Blue 104 are preferred. When the yellowing inhibitor (A) is an anthraquinone dye, the content of the anthraquinone dye as the yellowing inhibitor (A) is preferably 1 to 2400 ppm, more preferably 10 to 2000 ppm, even more preferably 100 to 1500 ppm, still more preferably 200 to 1500 ppm, still more preferably 200 to 700 ppm, and still more preferably 300 to 700 ppm, relative to the entire polyamide resin composition, from the viewpoint of effectively improving the color tone of both the container, etc. and the recycled polyester. The yellowing inhibitor (A) may be used alone or in combination of two or more.

[0031] Commercially available yellowing inhibitors (A) include MACROLEX Blue RR Gran (anthraquinone dye, manufactured by LANXESS), MACROLEX Blue 3R (1,4-bis[(2-ethyl-6-methylphenyl)amino]anthraquinone, an anthraquinone dye, manufactured by LANXESS), and Oracet Blue 690 (anthraquinone dye, manufactured by BASF).

[0032] <Color tone adjuster (B)> The polyamide resin composition of the present invention contains a color tone adjuster (B), and the solubility (Sa) of the yellowing inhibitor (A) in a 1.0% aqueous sodium hydroxide solution is smaller than the solubility (Sb) of the color tone adjuster (B) in a 1.0% aqueous sodium hydroxide solution, and the difference in solubility [(Sb) - (Sa)] is 100 mg / L or more. From the viewpoint of effectively improving the color tone of both the product such as the container and the recycled polyester, the content of the color tone adjuster (B) is preferably 0.1 to 6000 ppm, more preferably 1 to 6000 ppm, even more preferably 10 to 6000 ppm, still more preferably 100 to 4000 ppm, still more preferably 500 to 2000 ppm, and still more preferably 700 to 1500 ppm, relative to the entire polyamide resin composition. The mass ratio [(A) / (B)] of the content of the yellowing inhibitor (A) to the content of the color tone adjuster (B) contained in the polyamide resin composition is preferably 1 / 9 to 9 / 1, more preferably 1 / 9 to 8 / 2, even more preferably 1 / 9 to 5 / 5, still more preferably 1 / 9 to 4 / 6, and even more preferably 2 / 8 to 4 / 6, from the viewpoint of effectively improving the color tone of both the product such as a container and the recycled polyester.

[0033] The solubility (Sa) of the color tone adjuster (B) in a 1.0% aqueous sodium hydroxide solution is preferably 110 mg / L or more, more preferably 200 mg / L or more, and even more preferably 500 mg / L or more. When the solubility of the color tone adjuster (B) in a 1.0% aqueous sodium hydroxide solution is within the above range, the color tone of the product when used in a product such as a polyester-containing container is excellent, and further, the color tone of the recovered polyester obtained by recycling the product is also excellent. The difference [(Sb)-(Sa)] between the solubility (Sb) of the color tone adjuster (B) in a 1.0% aqueous sodium hydroxide solution and the solubility (Sa) of the yellowing inhibitor (A) in a 1.0% aqueous sodium hydroxide solution is 100 mg / L or more, preferably 110 mg / L or more, more preferably 200 mg / L or more, even more preferably 500 mg / L or more, and still more preferably 1000 mg / L or more. When the solubility difference is within the above range, the polyamide resin composition can be used in products such as polyester containers, resulting in excellent color tones for the products, and the recovered polyester obtained by recycling the products can also have excellent color tones.

[0034] The color tone adjuster (B) is preferably a compound having a yellow or orange color. The color tone of the color tone adjuster (B) can be confirmed by incorporating it into a polyamide resin. For example, the color tone of the color tone adjuster (B) can be measured using a polyamide resin (polyxylylene adipamide) containing 10 ppm of the color tone adjuster (B). Color b of polyamide resin containing 10 ppm of color adjuster (B) *is preferably greater than 0, more preferably greater than 1 and not greater than 30, and even more preferably greater than 2 and not greater than 15. The chromaticity of the polyamide resin containing 10 ppm of the color tone adjuster (B) can be obtained by measuring a 3 mm thick plate of polyxylylene adipamide containing 10 ppm of the color tone adjuster (B) with a colorimeter. Specifically, the same method as used to evaluate the recycled polyester in the Examples can be used. When the chromaticity is within the above range, the polyamide resin composition will have excellent color tone when used in products such as polyester containers, and the color tone of the recovered polyester obtained by recycling the product will also be excellent. The hue of the polyamide resin containing the color tone adjuster (B) is preferably the opposite color of the hue of the polyamide resin containing the yellowing inhibitor (A), and more preferably the complementary color of the hue of the polyamide resin containing the yellowing inhibitor (A).

[0035] The color tone adjusting agent (B) is preferably at least one selected from the group consisting of vitamin B compounds and quinophthalone compounds, and more preferably a vitamin B compound. The vitamin B compound is preferably a vitamin B2 compound. The vitamin B2 compound is preferably at least one selected from the group consisting of riboflavin and riboflavin derivatives, more preferably at least one selected from the group consisting of riboflavin, riboflavin tetrabutyrate, and riboflavin sodium phosphate, even more preferably at least one selected from the group consisting of riboflavin and riboflavin tetrabutyrate, and even more preferably riboflavin. The quinophthalone compound is preferably at least one selected from the group consisting of quinophthalone compounds having a hydroxyl group and quinophthalone compounds having a sulfo group, more preferably a quinophthalone compound having a hydroxyl group. Specifically, the quinophthalone compound is preferably at least one selected from the group consisting of Solvent Yellow 114 and Acid Yellow 3, more preferably Solvent Yellow 114.

[0036] <Other ingredients> The polyamide resin composition of the present invention may contain other components, such as a heat stabilizer, a light stabilizer, a moisture-proofing agent, a waterproofing agent, a lubricant, and a spreading agent. The polyamide resin composition of the present invention may contain resins other than the polyamide resin (Y) that is the main component, as long as the effects of the present invention are not impaired.

[0037] In the polyamide resin composition of the present invention, the total content of the polyamide resin (Y), the yellowing inhibitor (A), and the color tone adjuster (B) is preferably 80 to 100% by mass, more preferably 90 to 100% by mass, based on the total polyamide resin composition. The polyamide resin composition may consist solely of the polyamide resin (Y), the yellowing inhibitor (A), and the color tone adjuster (B). Furthermore, when a polyamide resin other than the polyamide resin (Y) is used in the masterbatch in the production of the polyamide resin composition described below, the total content of the polyamide resin (Y), the polyamide resin used in the masterbatch, the yellowing inhibitor (A), and the color tone adjuster (B) in the polyamide resin composition of the present invention is preferably 80 to 100% by mass, more preferably 90 to 100% by mass, based on the total polyamide resin composition. The polyamide resin composition may consist solely of the polyamide resin (Y), the polyamide resin used in the masterbatch, the yellowing inhibitor (A), and the color tone adjuster (B).

[0038] In the polyamide resin composition of the present invention, the content of the polyamide resin (Y) relative to the total resin content is preferably 80 to 100 mass %, more preferably 90 to 100 mass %. The resin constituting the polyamide resin composition may consist solely of the polyamide resin (Y).

[0039] <Method of producing polyamide resin composition> The polyamide resin composition of the present invention is a polyamide resin composition comprising a polyamide resin (Y), a yellowing inhibitor (A), and a color tone adjuster (B), wherein the solubility (Sa) of the yellowing inhibitor (A) in a 1.0% aqueous sodium hydroxide solution is smaller than the solubility (Sb) of the color tone adjuster (B) in a 1.0% aqueous sodium hydroxide solution, and the difference in solubility [(Sb) - (Sa)] is 100 mg / L or more. The production method is not limited, but it is preferable to produce it by the following method.

[0040] It is preferable to obtain the polyamide resin composition by melt-mixing the polyamide resin (Y), the yellowing inhibitor (A) and the color tone adjuster (B). Examples of the melt-mixing method include melt blending (melt kneading). When producing a multilayer container as described below, the polyamide resin (Y), the yellowing inhibitor (A), and the color tone adjuster (B) may be dry-blended in advance and then melt-mixed in the process of obtaining a multilayer preform. Examples of the melt blending method include the masterbatch method and the full compound method, and the masterbatch method is preferred from the viewpoint of preventing deterioration of the resin, the yellowing inhibitor, and the color tone adjuster.

[0041] The masterbatch method is a method in which a small amount of polyamide resin is kneaded with an anti-yellowing agent (A) and a color tone adjuster (B) to form a masterbatch, which is then mixed with the remaining polyamide resin (Y). The polyamide resin used in the masterbatch is preferably the polyamide resin (Y) from the viewpoint of miscibility with the polyamide resin (Y), and more preferably the same as the remaining polyamide resin (Y). The amount of polyamide resin used in the masterbatch is preferably 1 to 20 mass %, more preferably 3 to 15 mass %, based on the total amount of resin in the polyamide resin composition.

[0042] When a polyamide resin, a yellowing inhibitor (A), and a color tone adjuster (B) are kneaded to obtain a masterbatch, 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 thorough 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 more preferable, and 255 to 280°C is even more preferable. 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 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.

[0043] 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 process of obtaining a multilayer preform.

[0044] The full compounding method is a method in which the entire amount of polyamide resin (Y) used in the resin composition, the yellowing inhibitor (A), and the color tone adjuster (B) are kneaded and mixed. From the viewpoint of thorough mixing, the kneading temperature is preferably 245 to 300°C, more preferably 250 to 290°C, and even more preferably 255 to 280°C. 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 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.

[0045] [Multilayer container] The multilayer container of the present invention is a multilayer container having a polyester layer containing the polyester resin (X) and a polyamide layer containing the polyamide resin composition.

[0046] <Polyamide layer> The polyamide layer contains the polyamide resin composition. That is, the polyamide layer of the multilayer container of the present invention comprises a polyamide resin composition comprising a polyamide resin (Y), a yellowing inhibitor (A) and a color tone adjuster (B), wherein the solubility (Sa) of the yellowing inhibitor (A) in a 1.0% aqueous sodium hydroxide solution is smaller than the solubility (Sb) of the color tone adjuster (B) in a 1.0% aqueous sodium hydroxide solution, and the difference in solubility [(Sb) - (Sa)] is 100 mg / L or more. The polyamide resin composition contained in the polyamide layer is the one described above in the section [Polyamide Resin Composition], and the preferred polyamide resin composition is also the same as the one described above in the section [Polyamide Resin Composition]. The polyamide resin (Y), yellowing inhibitor (A), and color tone adjuster (B) contained in the polyamide layer are all the same as those described above in the sections <Polyamide resin (Y)>, <Yellowing inhibitor (A)>, and <Color tone adjuster (B)>, and preferred polyamide resins (Y), yellowing inhibitors (A), and color tone adjusters (B) are all the same as those described above in the sections <Polyamide resin (Y)>, <Yellowing inhibitor (A)>, and <Color tone adjuster (B)>.

[0047] The content of the polyamide resin composition 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, 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 composition or may consist solely of the polyamide resin composition. The content of the polyamide resin composition contained in the polyamide layer is preferably 0.05 to 7.0 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 the recycled polyester, it is more preferably 0.5 to 6.0 mass%, even more preferably 1.0 to 5.0 mass%, and still more preferably 1.5 to 4.5 mass%. The content of polyamide resin (Y) contained in the polyamide layer is preferably 0.05 to 7.0 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, it is more preferably 0.5 to 6.0 mass%, even more preferably 1.0 to 5.0 mass%, and still more preferably 1.5 to 4.5 mass%.

[0048] The content of the yellowing inhibitor (A) contained in the polyamide layer is preferably 1 to 2400 ppm, more preferably 10 to 2000 ppm, even more preferably 100 to 1500 ppm, still more preferably 200 to 1500 ppm, still more preferably 200 to 700 ppm, and still more preferably 300 to 700 ppm, relative to the total amount of the polyamide layer, from the viewpoint of effectively improving the color tone of both the container, etc. and the recycled polyester. The content of the yellowing inhibitor (A) contained in the polyamide layer is preferably 0.02 to 50 ppm, more preferably 0.2 to 40 ppm, even more preferably 2 to 40 ppm, still more preferably 4 to 40 ppm, still more preferably 4 to 20 ppm, and still more preferably 5 to 20 ppm, relative to the total amount of all polyamide layers and all polyester layers, from the viewpoint of effectively improving the color tone of both the container, etc. and the recycled polyester. When the yellowing inhibitor (A) is an anthraquinone dye, the content of the anthraquinone dye as the yellowing inhibitor (A) contained in the polyamide layer is preferably 1 to 2400 ppm, more preferably 10 to 2000 ppm, even more preferably 100 to 1500 ppm, still more preferably 200 to 1500 ppm, even more preferably 200 to 700 ppm, and even more preferably 300 to 700 ppm, relative to the total amount of the polyamide layer, from the viewpoint of effectively improving the color tone of both the container, etc. and the recycled polyester. When the yellowing inhibitor (A) is an anthraquinone dye, the content of the anthraquinone dye as the yellowing inhibitor (A) contained in the polyamide layer is preferably 0.02 to 50 ppm, more preferably 0.2 to 40 ppm, even more preferably 2 to 40 ppm, still more preferably 4 to 40 ppm, even more preferably 4 to 20 ppm, and even more preferably 5 to 20 ppm, relative to the total amount of all polyamide layers and all polyester layers, from the viewpoint of effectively improving the color tone of both the container, etc. and the recycled polyester.

[0049] The content of the color tone adjuster (B) contained in the polyamide layer is preferably 0.1 to 6000 ppm, more preferably 1 to 5000 ppm, even more preferably 10 to 5000 ppm, still more preferably 100 to 4000 ppm, still more preferably 500 to 2000 ppm, and still more preferably 700 to 1500 ppm, relative to the total amount of the polyamide layer, from the viewpoint of effectively improving the color tone of both the product such as the container and the recycled polyester. The content of the color tone adjuster (B) contained in the polyamide layer is preferably 0.002 to 150 ppm, more preferably 0.02 to 120 ppm, even more preferably 0.2 to 120 ppm, still more preferably 3 to 100 ppm, still more preferably 12 to 50 ppm, and even more preferably 15 to 40 ppm, relative to the total amount of all polyamide layers and all polyester layers, from the viewpoint of effectively improving the color tone of both the product such as the container and the recycled polyester. The mass ratio [(A) / (B)] of the content of the yellowing inhibitor (A) to the content of the color tone adjuster (B) contained in the polyamide layer is preferably 1 / 9 to 9 / 1, more preferably 1 / 9 to 8 / 2, even more preferably 1 / 9 to 5 / 5, still more preferably 1 / 9 to 4 / 6, and even more preferably 2 / 8 to 4 / 6, from the viewpoint of effectively improving the color tone of both the product such as the container and the recycled polyester.

[0050] <Polyester layer> The polyester layer contains a polyester resin (X).

[0051] (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 constitutional unit derived from a dicarboxylic acid (dicarboxylic acid unit) and a constitutional unit derived from a diol (diol unit).

[0052] Examples of the dicarboxylic acid unit include a structural unit derived from an aromatic dicarboxylic acid, a structural unit derived from an alicyclic dicarboxylic acid, and a structural unit derived from an aliphatic dicarboxylic acid, with a structural unit derived from an aromatic dicarboxylic acid being preferred. Examples of aromatic dicarboxylic acids include terephthalic acid, isophthalic acid, orthophthalic acid, biphenyldicarboxylic acid, diphenyletherdicarboxylic acid, diphenylsulfonedicarboxylic acid, diphenylketonedicarboxylic 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, and terephthalic acid, isophthalic acid, and naphthalenedicarboxylic acid are more preferred. From the viewpoint of moldability, terephthalic acid and isophthalic acid are even more preferred, and terephthalic acid is even more preferred. When the multilayer container of the present invention is recycled, it may be melt-kneaded with a conventional single-layer container made of a polyester resin. By containing units derived from terephthalic acid as dicarboxylic acid units, the compatibility between the multilayer container of the present invention and the conventional single-layer container is improved, resulting in good recyclability.

[0053] The aromatic dicarboxylic acid may be sulfophthalic acid or a metal salt of sulfophthalic acid. The metal salt of sulfophthalic acid is a metal salt of sulfophthalic acid, and the metal atom may be an alkali metal or an alkaline earth metal. Examples of the alicyclic dicarboxylic acid include cyclohexanedicarboxylic acid, norbornenedicarboxylic acid, and tricyclodecanedicarboxylic acid. Examples of the aliphatic dicarboxylic acid include malonic acid, succinic acid, adipic acid, azelaic acid, and sebacic acid.

[0054] Examples of the diol unit include a structural unit derived from an aliphatic diol, a structural unit derived from an alicyclic diol, and a structural unit derived from an aromatic diol, with a structural unit derived from an aliphatic diol being preferred. Examples of the aliphatic diol 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. Alicyclic diols include cyclohexanedimethanol, isosorbide, spiroglycol, 2,2,4,4-tetramethyl-1,3-cyclobutanediol, norbornene dimethanol, and tricyclodecane dimethanol. Aromatic diols include bisphenol compounds and hydroquinone compounds.

[0055] 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 acid include 10-hydroxyoctadecanoic acid, lactic acid, hydroxyacrylic acid, 2-hydroxy-2-methylpropionic acid, and hydroxybutyric acid. Examples of the alicyclic hydroxycarboxylic acid include hydroxymethylcyclohexanecarboxylic acid, hydroxymethylnorbornenecarboxylic acid, and hydroxymethyltricyclodecanecarboxylic acid. Examples of aromatic hydroxycarboxylic acids include hydroxybenzoic acid, hydroxytoluic acid, hydroxynaphthoic acid, 3-(hydroxyphenyl)propionic acid, hydroxyphenylacetic acid, and 3-hydroxy-3-phenylpropionic acid.

[0056] 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, and specific examples thereof include 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 polyhydric alcohols, alicyclic polyhydric alcohols, and esters thereof.

[0057] The polyester resin (X) preferably has structural units derived from a dicarboxylic acid containing structural units derived from terephthalic acid and structural units derived from a diol containing structural units derived from ethylene glycol; more preferably 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; still more preferably has structural units derived from a dicarboxylic acid containing 90 mol% or more of structural units derived from terephthalic acid and structural units derived from a diol containing 90 mol% or more of structural units derived from ethylene glycol; and still more preferably has structural units derived from a dicarboxylic acid containing 98 mol% or more of structural units derived from terephthalic acid and structural units derived from a diol containing substantially 100 mol% of structural units derived from ethylene glycol. A specific example of the polyester resin (X) is polyethylene terephthalate (PET).

[0058] Polyethylene terephthalate (PET) may contain structural units derived from aromatic dicarboxylic acids other than terephthalic acid. The aromatic dicarboxylic acids other than terephthalic acid are preferably one or more selected from isophthalic acid, orthophthalic acid, naphthalenedicarboxylic acid, and 4,4'-biphenyldicarboxylic acid. These are low in cost, and copolymer 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 is superior in preventing whitening of molded articles due to a slower crystallization rate. Furthermore, polyethylene terephthalate containing structural units derived from naphthalenedicarboxylic acid increases the glass transition point of the resin, improving heat resistance, and also absorbs ultraviolet light, making it suitable for use in the production of multilayer containers that require resistance to ultraviolet light. As the naphthalenedicarboxylic acid, 2,6-naphthalenedicarboxylic acid is preferred because it is easy to produce and highly economical. When polyethylene terephthalate contains structural units derived from aromatic dicarboxylic acids other than terephthalic acid, the proportion of the structural units derived from aromatic dicarboxylic acids other than terephthalic acid is preferably 1 to 20 mol %, more preferably 1 to 10 mol %, and even more preferably 1 to 5 mol % of the dicarboxylic acid units.

[0059] 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 an ester exchange method.

[0060] 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 more, the mechanical properties of the container are excellent. The intrinsic viscosity is measured by dissolving the polyester resin in a mixed solvent of phenol / 1,1,2,2-tetrachloroethane (=6 / 4 mass ratio) to prepare 0.2, 0.4, and 0.6 g / dL solutions, and measuring them at 25°C using an automatic viscosity measuring device (manufactured by Malvern, Viscotek).

[0061] (Other ingredients) The polyester layer may contain other components such as 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) as 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 mass %, more preferably 90 to 100 mass %, based on the total resin amount of the polyester layer, and the polyester layer may consist solely of the polyester resin (X).

[0062] <Structure and characteristics of multi-layer containers> The multilayer container of the present invention is a multilayer container having a polyester layer containing the polyester resin (X) and a polyamide layer containing the polyamide resin composition. The multilayer container of the present invention may contain resin layers other than the polyester layer and the polyamide layer, but from the viewpoint of facilitating separation during recycling and improving the color tone of the container and the recovered polyester, the content of resin layers other than the polyester layer and the polyamide layer is preferably small, and it is preferable that the container is 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 substance may be provided, but from the viewpoint of facilitating separation during recycling and improving the yellowing suppression effect, the content of adhesive layers or inorganic layers is preferably small, and it is preferable that the container is substantially free of adhesive layers or inorganic layers.

[0063] 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 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, and the innermost layer is also preferably a polyester layer, and it is more preferable that both the outermost layer and the innermost layer 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 preferably has 2 to 5 layers, with the outermost layer being a polyester layer, and more preferably has 3 to 5 layers, with the outermost and innermost layers being polyester layers.

[0064] 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.

[0065] The multilayer container of the present invention is preferably a hollow container, and when the multilayer container is a hollow container, at least the body 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 (thickness ratio W / S) is preferably 2.5 or more and 200 or less. The thickness of the polyester layer means the average thickness, and when the body 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 method of recycled polyester, particularly winnowing separation and gravity separation. Also, a thickness ratio W / S of 200 or less provides excellent gas barrier properties for the hollow container, allowing the contents to be stored for a long period of time. From the viewpoint of improving the gas barrier properties of the hollow container while increasing the separability in the separation step, the thickness ratio (W / S) is more preferably 3-50, and further preferably 4-15.

[0066] 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.

[0067] The content of the yellowing inhibitor (A) contained in the multilayer container is preferably 0.02 to 80 ppm, more preferably 0.2 to 70 ppm, even more preferably 2 to 50 ppm, still more preferably 4 to 35 ppm, even more preferably 4 to 25 ppm, and even more preferably 5 to 25 ppm, relative to the total amount of all polyamide layers and all polyester layers, from the viewpoint of effectively improving the color tone of both the product such as the container and the recycled polyester. The content of the color tone adjuster (B) contained in the multilayer container is preferably 0.002 to 200 ppm, more preferably 0.02 to 200 ppm, even more preferably 0.2 to 200 ppm, still more preferably 3 to 150 ppm, even more preferably 5 to 60 ppm, and even more preferably 10 to 50 ppm, relative to the total amount of all polyamide layers and all polyester layers, from the viewpoint of effectively improving the color tone of both the product such as the container and the recycled polyester.

[0068] 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. The liquid to be filled inside includes 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. Liquid seasonings include sauces, soy sauce, syrups, mirin, dressings, etc. Chemicals include pesticides, insecticides, and the like.

[0069] <Manufacturing method for multilayer containers> The method for producing the multilayer container of the present invention is not particularly limited as long as it is a method for producing a multilayer container having a polyester layer containing polyester resin (X) and a polyamide layer containing the polyamide resin composition, but it is preferably a production method including the following steps 1 and 2: That is, the method for producing a multilayer container of the present invention preferably comprises the following steps 1 and 2, and the multilayer container has a polyester layer containing polyester resin (X) and a polyamide layer containing the polyamide resin composition. Step 1: A step of co-injecting the polyamide resin composition or polyamide resin mixture and a polyester resin composition containing a polyester resin (X) to obtain a multi-layer preform. Step 2: Blow molding the multilayer preform

[0070] <Step 1 (Step for obtaining a multilayer preform)> In step 1, the polyamide resin composition or polyamide resin mixture and a polyester resin composition containing a polyester resin (X) are co-injection molded to obtain a multi-layer preform. The polyamide resin composition is the polyamide resin composition described above in the section [Polyamide Resin Composition]. The polyamide resin mixture refers to a mixture obtained by dry-blending the polyamide resin (Y), the yellowing inhibitor (A), and the color tone adjuster (B) described above in the section <Production method of polyamide resin composition>, or a mixture obtained by dry-blending the masterbatch with the remaining polyamide resin (Y). These polyamide resin mixtures become the polyamide resin compositions described above in the section [Polyamide resin composition] by melt-mixing the components in this step. The polyester resin composition preferably has the same composition as the <polyester layer> except for the polyester resin (X). In co-injection molding, a mixture of polyester resin and polyamide resin is separately extruded into a mold and co-injection molded to form a multi-layer preform.

[0071] <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, 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 in step 2. 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.

[0072] [Manufacturing method of recycled polyester] The method for producing recycled polyester of the present invention is a method for producing recycled polyester, which comprises a step of washing the multilayer container or its pulverized product with an alkaline aqueous solution and recovering the polyester. That is, the method for producing recycled polyester of the present invention is a method for producing recycled polyester, which includes a step of washing a multilayer container having a polyester layer containing polyester resin (X) and a polyamide layer containing the polyamide resin composition, or a pulverized product thereof, with an alkaline aqueous solution and recovering the polyester. Specifically, the polyamide resin composition comprises a polyamide resin (Y), a yellowing inhibitor (A), and a color tone adjuster (B), wherein the solubility (Sa) of the yellowing inhibitor (A) in a 1.0% aqueous sodium hydroxide solution is smaller than the solubility (Sb) of the color tone adjuster (B) in a 1.0% aqueous sodium hydroxide solution, and the difference in solubility [(Sb)-(Sa)] is 100 mg / L or more. The method for producing the recycled polyester of the present invention will be described in detail below.

[0073] In the present manufacturing method, a used multilayer container is usually used, but an unused multilayer container may also be used. Examples of used multilayer containers include those that have been once distributed on the market and then collected. In this manufacturing method, first, if a lid is attached to the multilayer container, it is preferable to remove the lid from the multilayer container. Next, the container is crushed, and if necessary, separation is carried out to selectively extract the polyester, which is then recovered as recycled polyester (recovery step). In the recovery step, the container or the pulverized material is washed with an alkaline aqueous solution (washing step). Next, if necessary, the mixture is granulated to form pellets (granulation step). Furthermore, if necessary, a crystallization step and a solid-state polymerization step are carried out (crystallization / solid-state polymerization step). Each step will be explained below.

[0074] <Cleaning process> In the method for producing recycled polyester of the present invention, the multilayer container or its pulverized product is washed with an alkaline aqueous solution to recover the polyester. Washing with an alkaline aqueous solution makes it possible to efficiently remove not only the contents stored in the multilayer container but also adhesives, etc. Furthermore, in the production method of the present invention, the color tone adjuster (B) contained in the multilayer container can be efficiently removed, and yellowing of the resulting recycled polyester can be suppressed. The washing with the alkaline aqueous solution may be performed in the container, simultaneously with pulverization, after pulverization, or after separation into polyester and polyamide resin. Furthermore, washing may be performed multiple times. Although washing after pulverization is preferred, for convenience, the washing step will be described before the recovery step described below.

[0075] The solvent of the alkaline aqueous solution used to wash the multilayer container or its crushed product is water from the viewpoints of washing efficiency and cost. In addition to water, the aqueous 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 more preferably an alkali metal hydroxide from the viewpoints of cleaning efficiency and cost. Examples of alkali metal hydroxides include sodium hydroxide, potassium hydroxide, and lithium hydroxide. From the standpoint 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 mass %, more preferably 0.5 to 8 mass %, and even more preferably 1 to 5 mass %, based on the total amount of the alkaline aqueous solution.

[0076] Any type of washing device may be used, but it is preferable to use a vessel equipped with a stirrer, particularly 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, shape, etc. of the multilayer container or pulverized material.

[0077] 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.

[0078] <Recovery process> The recovery step is a step of crushing the multilayer container and recovering the recycled polyester. In particular, it is 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 that constitutes the polyamide layer. The multilayer container can be crushed using a crusher such as a single-axis crusher, a twin-axis crusher, a triple-axis crusher, or a cutter mill. The crushed material obtained by crushing can be, for example, in the form of flakes, powder, or lumps. However, since most of the multilayer container has a thin, multilayer laminate structure with a thickness of a few 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.

[0079] In addition, in a multilayer container, the polyester layer and the polyamide layer are structurally integrated, but they are not usually adhered to each other, and in the pulverization process, the polyester and polyamide resins are easily separated as separate pulverized materials. Furthermore, by forming them into flakes, they can be easily separated by being blown up by the air current during the winnowing separation process described below. However, polyester and polyamide resin cannot be completely separated in the pulverization process, and the pulverized material is separated into one with a relatively high polyester content and one with a relatively low polyester content and a relatively high polyamide resin content. Hereinafter, for the sake of convenience, the material with a relatively high polyester content will be simply referred to as polyester, and the material with a relatively high polyamide resin content will be simply referred to as polyamide resin.

[0080] As described above, the pulverized material is separated into polyester and polyamide resin (separation step). As a method for separating the polyester and polyamide resins, it is preferable to use gravity separation, which utilizes the difference in specific gravity between the polyester and polyamide resins. That is, it is preferable to remove the polyamide layer by crushing the multilayer container and then separating the crushed polyamide layer by winnowing. A specific example of gravity separation is winnowing, which separates pulverized materials using wind power. Winnowing is a method in which, for example, pulverized materials exposed to the airflow generated by a separator capable of generating a rotating airflow inside the separator are separated and recovered into those with a high specific gravity or a small specific surface area that fall naturally under their own weight and those with a low specific gravity or a large specific surface area that are blown up by the airflow. In this method, the pulverized polyester material falls naturally under its own weight, while the pulverized polyamide resin material is lifted up, making it possible to separate and recover the polyester and polyamide resin. In this type of winnowing, the same operation may be repeated for the same pulverized material. For example, the material that has fallen naturally may be further winnowed to increase the polyester content in the recycled polyester. The separation method is not limited to winnowing, and may include a method of immersing the crushed material in a liquid such as water and separating it based on the difference in specific gravity of the crushed material relative to the liquid, or a method of applying a certain amount of vibration to the crushed material to separate and separate crushed material with different specific gravities.

[0081] <Granulation process> The recovered recycled polyester is preferably granulated into pellets to facilitate handling during molding and other processes. Granulation may be carried out either before or after the crystallization / solid-state polymerization step described below, but it is better to carry out the granulation before the crystallization / solid-state polymerization step. By carrying out the granulation before the crystallization / solid-state polymerization step, handling in the crystallization / solid-state polymerization step becomes easier. In the granulation step, the pulverized material is preferably plasticized and granulated by melt blending. 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 shape of the pellets is preferably cylindrical, spherical, or elliptical. The granulation is preferably carried out, for example, by extruding the plasticized recycled polyester into a strand, cooling it in a water bath, and cutting it into pellets using a pelletizer. The pellets removed from the water bath are usually dried to remove moisture adhering to the surface.

[0082] <Crystallization / solid phase polymerization process> 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 above-mentioned pelletized polyester, but may also be carried out on an unpelletized product (for example, 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, for example, at 100 to 230°C. The crystallization of the polyester prevents the polyester from fusing with itself or adhering to the inner surface of the device during solid-state polymerization or molding processing.

[0083] Solid-state polymerization is preferably carried out by maintaining a temperature at or above (the melting point of the polyester minus 80°C) but below the melting point of the polyester for a certain period of time. Maintaining the temperature below the melting point prevents the polyester from melting, which prevents, for example, the polyester from adhering to the surface of the apparatus and reducing work efficiency. Furthermore, maintaining the temperature at or above (the melting point of the polyester minus 80°C) allows the polymerization to proceed at a sufficient rate, making it easier to obtain the desired physical properties. Here, "(the melting point of the polyester minus 80°C)" means "a temperature 80°C lower than the melting point of the polyester."

[0084] Solid-state polymerization may be carried out under vacuum or in a stream of an inert gas 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 a stream of an inert gas 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 solid-state polymerization is carried out in the presence of an inert gas, it is preferable to maintain a state in which the surface of the polyester is constantly in contact with the dry gas under a dry gas stream.

[0085] Examples of solid-state polymerization apparatuses for carrying out the crystallization / solid-state polymerization step include a tumbler-type batch apparatus equipped with a heating jacket, a dry silo-type apparatus equipped with an inert gas flow facility, a crystallization apparatus and reactor equipped with an internal stirring blade and discharge screw, etc. It is preferable that the 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 taking into consideration the apparatus and other conditions, but it is sufficient if it is a time that allows the polyester to acquire sufficient physical properties. In solid-state polymerization, polyester is maintained at high temperatures for a long period of time, and therefore, if impurities are present in the polyester, this can deteriorate the quality of the polyester, such as color tone. It is preferable that most of the polyamide resin is removed in the removal step described above, and in this case, deterioration in quality that may occur during solid-state polymerization can be minimized.

[0086] 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. In the method for producing recycled polyester of the present invention, steps other than those described above may be carried out.

[0087] The recycled polyester obtained by this production method can be used for various purposes such as resin moldings and fibers. [Example]

[0088] 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.

[0089] [Raw materials] The polyester resin, yellowing inhibitor, and color tone adjuster used in the examples and comparative examples are as follows: The polyamide resin used was that produced in Production Example 1 below. <Polyester resin> Polyclear Refresh PET 1101, polyethylene terephthalate (Indorama) <Yellowing inhibitor (A)> Blue RR: Solvent Blue 97 (anthraquinone dye, trade name: MACROLEX Blue RR Gran, manufactured by LANXESS, solubility in 1.0% sodium hydroxide solution (Sa): less than 10 mg / L) Violet 3R: Solvent Violet 36 (anthraquinone dye, trade name: MACROLEX Violet 3R Gran, manufactured by LANXESS, solubility in 1.0% sodium hydroxide solution (Sa): less than 10 mg / L) Blue 690: Solvent Blue 104 (anthraquinone dye, trade name: Oracet Blue 690, manufactured by BASF, solubility in 1.0% sodium hydroxide solution (Sa): less than 10 mg / L) <Color tone adjuster (B), etc.> Riboflavin: Riboflavin (vitamin B2 compound, vitamin B compound, solubility in 1.0% sodium hydroxide solution (Sb): greater than 500 mg / L) Riboflavin tetrabutyrate: Riboflavin tetrabutyrate (vitamin B2 compound, vitamin B compound, solubility in 1.0% sodium hydroxide solution (Sb): 300 mg / L) Solvent Yellow 114: 2-(3-hydroxy-2-quinolinyl)-1,3-indandione (a quinophthalone compound with a hydroxyl group, solubility in 1.0% sodium hydroxide solution (Sb): 200 mg / L) Acid Yellow 3: Sodium 2-(1,3-dioxoindan-2-yl)quinolinedisulfonate (a quinophthalone compound with a sulfo group; solubility in 1.0% sodium hydroxide solution (Sb): greater than 500 mg / L) Solvent Yellow 179: Methine compound (solubility in 1.0% sodium hydroxide solution: less than 10 mg / L)

[0090] <Polyamide resin> Production Example 1 (Production of Polyamide Resin (Y1)) A 50-liter reactor equipped with a stirrer, partial condenser, total condenser, thermometer, dropping funnel, nitrogen inlet tube, and strand die was charged with precisely weighed 15,000 g (102.6 mol) of adipic acid, 13.06 g (123.3 mmol) of sodium hypophosphite monohydrate (NaH2PO2·HO), and 6.849 g (83.49 mmol) of sodium acetate (0.68 molar ratio to sodium hypophosphite monohydrate). After thorough nitrogen purge, the system was heated to 170°C with stirring under a small nitrogen stream. To this was added dropwise 13,896 g (102.0 mol) of metaxylylenediamine (0.994 molar ratio) with stirring, and the temperature was continuously raised while the resulting condensation water was removed from the system. After the dropwise addition of metaxylylenediamine was completed, the internal temperature was raised to 260° C. and the reaction was continued for 40 minutes. Thereafter, the system was pressurized with nitrogen, and the polymer was removed from the strand die and pelletized to obtain about 24 kg of polyamide. The polyamide was then 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 inside 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.

[0091] Examples 1 to 7 and Comparative Examples 1 to 4 [Production of polyamide resin composition, multilayer container, and recycled polyester] <1. Production of polyamide resin composition> The production of the polyamide resin composition of each example and comparative example is described below. The multilayer container and the recycled polyester were produced in the same manner in all examples and comparative examples. Example 1 99.86% by mass of polyamide resin (Y1), 0.02% by mass of Blue RR and 0.02% by mass of Violet 3R as yellowing inhibitors (A), and 0.10% by mass of riboflavin as a color tone adjuster (B) were dry-blended in advance. Next, this dry-blended mixture was melt-kneaded at 260°C using a twin-screw extruder (TEM26SX, manufactured by Toshiba Machine Co., Ltd.) to obtain a polyamide resin composition.

[0092] Examples 2 to 7 A polyamide resin composition was obtained in the same manner as in Example 1, except that the types and amounts of the yellowing inhibitor (A) and the color tone adjuster (B) were changed as shown in Table 1.

[0093] (Comparative Example 1) A polyamide resin composition was obtained in the same manner as in Example 1, except that the yellowing inhibitor (A) and the color tone adjuster (B) were not used.

[0094] (Comparative Example 2) A polyamide resin composition was obtained in the same manner as in Example 1, except that the color tone adjuster (B) was not used.

[0095] (Comparative Example 3) A polyamide resin composition was obtained in the same manner as in Example 1, except that the yellowing inhibitor (A) was not used.

[0096] Comparative Example 4 A polyamide resin composition was obtained in the same manner as in Example 1, except that 0.01% by mass of Solvent Yellow 179 was used instead of 0.10% by mass of riboflavin, which is the color tone adjuster (B).

[0097] <2. Manufacturing of multi-layer containers> (preform molding) Using an injection molding machine (Sumitomo Heavy Industries, Ltd., Model DU130CI) with two injection cylinders and a two-cavity mold (Kortec), a polyester resin (Polyclear Refresh PET 1101) was injected through one injection cylinder, and the polyamide resin composition obtained in <1. Production of Polyamide Resin Composition> above was injected through the other injection cylinder. Three-layer preforms (each preform weighing 25 g) consisting of a polyester layer, a polyamide layer, and a polyester layer were injection molded 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 preform had a total length of 95 mm, an outer diameter of 22 mm, and a wall thickness of 4.0 mm. The molding conditions for the three-layer preform were as shown below. Skin side injection cylinder temperature: 285℃ Core side injection cylinder temperature (3 layers only): 265℃ Resin flow path temperature in the mold: 285℃ Mold cooling water temperature: 15℃ Cycle time: 40 seconds

[0098] (bottle molding) The preform obtained in the above (preform molding) was biaxially stretch blow molded using a blow molding machine (EFB1000ET, 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 in the body. The biaxial stretch blow molding conditions were as follows: Preform heating temperature: 103℃ Pressure for stretching rod: 0.7MPa Primary blow pressure: 1.1 MPa Secondary blow pressure: 2.5MPa Primary blow delay time: 0.30 seconds First blow time: 0.30 seconds Secondary blow time: 2.0 seconds Blow exhaust time: 0.6 seconds Mold temperature: 30℃

[0099] <3. Production of recycled polyester> (Washing, recovery, granulation process) 10 kg of the hollow multilayer container obtained in <2. Production of multilayer container> above was pulverized in a pulverizer with a mesh size of 10 mm. 1 kg of the obtained flaky pulverized material was placed in a container equipped with a stirrer, and 4 L of 1% sodium hydroxide aqueous solution was added, and washed while stirring. The washing temperature was 85°C, and the washing time was 15 minutes. After removing the washing water, the pulverized material was placed in 45°C water of 4 times the mass of the pulverized material and stirred for 5 minutes. After dehydration, water of 8 times the mass of the pulverized material was added and stirred. After dehydration, the washed pulverized material was dried at 50°C. The dried pulverized material was extruded into strands using a twin-screw extruder (Toshiba Machine Co., Ltd., TEM26SX) 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 air separation.

[0100] (Crystallization / solid phase polymerization process) 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.

[0101] [Evaluation method] <Preparing samples for evaluation> The following L * value, a * value, b * The evaluation samples for measuring the value and haze were prepared as follows. Evaluation samples of the multilayer container were obtained by cutting out the body portion of the bottle (multilayer container) of each of the examples and comparative examples at a height of 5 to 9 cm from the bottom. The evaluation samples of the recycled polyester were produced by injection molding the heat-treated pellets of the Examples and Comparative Examples into plates measuring 60 mm in length, 90 mm in width, and 3.0 mm in thickness using an injection molding machine with an injection cylinder (manufactured by Sumitomo Heavy Industries, Ltd., model SE130DU-HP) under the molding conditions shown below. Injection cylinder temperature: 280℃ Mold cooling water temperature: 15℃ Cycle time: 45 seconds

[0102] * Value> According to JIS K 7105, the haze of the evaluation sample was measured using a haze meter COH400 (manufactured by Nippon Denshoku Industries Co., Ltd.). * The values ​​were measured. In addition, b * The value represents the chromaticity. * is yellow direction, -b * b indicates the blue direction. * The smaller the absolute value of the value, the better the colorlessness and color tone. * The absolute value of the value is small and b * The higher the value, the less blue it is, the better the colorlessness and color tone. * 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.

[0103] <L * Value> According to JIS K 7105, the haze of the evaluation sample was measured using a haze meter COH400 (manufactured by Nippon Denshoku Industries Co., Ltd.). * The value was measured. * The value represents the lightness, L * The larger the value, the higher the whiteness, which is preferable.

[0104] * Value> According to JIS K 7105, the haze of the evaluation sample was measured using a haze meter COH400 (manufactured by Nippon Denshoku Industries Co., Ltd.). * The values ​​were measured. In addition, a * The value represents the chromaticity. * is red direction, -a * represents the green direction. * The smaller the absolute value, the better the colorlessness and color tone, which is preferable.

[0105] <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., with a 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.

[0106] [Table 1]

[0107] As shown in Table 1, the multilayer container of the present invention has little blue color and is excellent in colorlessness, and the recycled polyester obtained by recycling the multilayer container has little yellow color and is excellent in colorlessness. * In Comparative Example 2, the value of b of the multilayer container is large and yellowing is observed. * In particular, in Comparative Example 4, despite the use of a yellowing inhibitor and a color tone adjuster in combination, the difference in solubility was less than 10 mg / L, and the b value of the recycled polyester was * This shows that by using the polyamide resin composition of the present invention in products such as polyester-containing containers, the color tone of the finished containers and the like is excellent, and furthermore, the color tone of the recovered polyester obtained by recycling the products is also excellent.

Claims

1. A polyamide resin composition comprising a polyamide resin (Y), a yellowing inhibitor (A), and a color tone adjuster (B), wherein the solubility (Sa) of the yellowing inhibitor (A) in a 1.0% aqueous sodium hydroxide solution is smaller than the solubility (Sb) of the color tone adjuster (B) in a 1.0% aqueous sodium hydroxide solution, and the difference in solubility [(Sb) - (Sa)] is 100 mg / L or more.

2. 2. The polyamide resin composition according to claim 1, wherein the color tone adjuster (B) is a color tone adjuster that causes a polyamide resin containing 10 ppm of the color tone adjuster (B) to have a chromaticity b* of greater than 0.

3. 2. The polyamide resin composition according to claim 1, wherein the solubility (Sa) of the yellowing inhibitor (A) in a 1.0% aqueous sodium hydroxide solution is 100 mg / L or less.

4. 2. The polyamide resin composition according to claim 1, wherein the yellowing inhibitor (A) is an anthraquinone dye.

5. 2. The polyamide resin composition according to claim 1, wherein the color tone adjuster (B) is at least one selected from the group consisting of vitamin B compounds and quinophthalone compounds.

6. 2. The polyamide resin composition according to claim 1, wherein the content of the yellowing inhibitor (A) is 100 to 1500 ppm based on the total content of the polyamide resin composition.

7. 2. The polyamide resin composition according to claim 1, wherein the content of the color tone adjuster (B) is 10 to 6,000 ppm based on the total content of the polyamide resin composition.

8. 2. The polyamide resin composition according to claim 1, 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.

9. A multilayer container having a polyester layer containing a polyester resin (X) and a polyamide layer containing the polyamide resin composition according to any one of claims 1 to 8.

10. 10. The multilayer container according to claim 9, wherein the content of the polyamide resin composition is 0.05 to 7.0% by mass based on the total amount of all polyamide layers and all polyester layers.

11. 10. The multilayer container according to claim 9, 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.

12. 10. The multi-layer container according to claim 9, wherein the multi-layer container is a multi-layer hollow container.

13. 10. The multilayer container according to claim 9, wherein the multilayer container has a 3 to 5 layer structure, and the outermost layer and the innermost layer are polyester layers.

14. A method for producing recycled polyester, comprising the step of washing the multilayer container according to claim 9 or a crushed product thereof with an alkaline aqueous solution to recover the polyester.