Multilayer container, method of manufacturing the same, and method of manufacturing recycled polyester

Abstract

A multilayer container having a polyester layer containing a polyester resin (X) and a polyamide layer containing a polyamide resin (Y), a yellowing inhibitor (A), and an oxidation promoter (B), wherein the content of the polyamide resin (Y) is 0.05 to 7.0 mass% relative to the total amount of the polyamide layer and the total polyester layer, the yellowing inhibitor (A) is a dye, and the content of the yellowing inhibitor (A) is 1 to 30 ppm relative to the total amount of the polyamide layer and the total polyester layer.

Description

Technology Field

[0001] The present invention relates to a multilayer container, a method for manufacturing the same, and a method for manufacturing recycled polyester. Background Technology

[0002] Aromatic polyester resins, obtained by using aromatic dicarboxylic acid compounds and aliphatic diol compounds as monomers, possess excellent characteristics such as transparency, mechanical performance, melt stability, solvent resistance, scent retention, gas barrier properties, and recyclability. For this reason, aromatic polyester resins, such as polyethylene terephthalate (PET), are widely used in various packaging materials, including films, sheets, and hollow containers. While polyester resins possess high gas barrier properties, they are not necessarily sufficient for applications requiring additional gas barrier properties against oxygen, carbon dioxide, etc. Therefore, as a means to improve the gas barrier properties of polyester resins, methods are employed such as depositing aluminum oxide or silicon oxide onto molded bodies or packaging containers made of polyester resin, or coating, laminating, or melt-mixing resins with high gas barrier performance onto the molded bodies 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, polyxylylene adipamide, obtained by polymerizing a diamine component with xylylenediamine as the main component and a dicarboxylic acid component with adipic acid as the main component, exhibits excellent gas barrier properties. In addition to possessing high gas barrier properties, polyxylylene adipamide is easy to laminate and melt-mix with polyester resins because its glass transition temperature, melting point, and crystallinity are similar to those of polyethylene terephthalate, a widely used polyester resin. For this reason, polyxylylene adipamide is highly suitable as a material for improving the gas barrier properties of polyester resins.

[0004] However, polyester resin compositions containing polyamide are more prone to yellowing due to thermal history compared to polyester alone. Consequently, yellowing occurs particularly in the recycling process where containers are recovered and resins are reused. Since this is a factor that lowers 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 inhibition ability, a polyamide resin layer containing a polyamide resin, and a method for manufacturing recycled polyester. Prior art literature

[0005] International Publication No. 2017 / 057463 The problem to be solved

[0006] Since the yellowing of recycled polyester is largely influenced by oxidation, and using oxygen-absorbing materials in the container exacerbates the yellowing, it is difficult to improve the oxygen barrier properties of the container; therefore, there was a demand for a container capable of achieving both yellowing suppression and high oxygen barrier properties.

[0007] Accordingly, the present invention aims to provide a multilayer container with excellent oxygen barrier properties capable of suppressing yellowing of recycled polyester during recycling, and a method for manufacturing recycled polyester with suppressed yellowing. means of solving the problem

[0008] The inventors, after careful consideration of the above problem, discovered that a multilayer container having a polyester layer and a polyamide layer containing a polyamide resin, a specific yellowing inhibitor, and an oxidation promoter can solve the above problem, and thus completed the present invention.

[0009] The present invention provides the following [1] to

[25] .

[0010] [1] A multilayer container having a polyester layer containing a polyester resin (X) and a polyamide layer containing a polyamide resin (Y), a yellowing inhibitor (A) and an oxidation promoter (B), wherein the content of the polyamide resin (Y) is 0.05 to 7.0 mass% relative to the total amount of the polyamide layer and the total polyester layer, the yellowing inhibitor (A) is a dye, and the content of the yellowing inhibitor (A) is 1 to 30 ppm relative to the total amount of the polyamide layer and the total polyester layer.

[0011] [2] A multilayer container described in [1], wherein the polyester resin (X) has a constituent unit derived from a dicarboxylic acid containing 80 mol% or more of a constituent unit derived from terephthalic acid and a constituent unit derived from a diol containing 80 mol% or more of a constituent unit derived from ethylene glycol.

[0012] [3] A multilayer container described in [1] or [2], wherein the polyamide resin (Y) has a diamine-derived unit containing 80 mol% or more of a constituent unit derived from xylylenediamine and a dicarboxylic acid-derived unit containing 80 mol% or more of a constituent unit derived from adipic acid.

[0013] [4] A multilayer container described in any one of [1] to [3], wherein the oxidation promoter (B) is a compound containing a transition metal.

[0014] [5] A multilayer container described in [4], wherein the transition metal is at least one selected from the group consisting of cobalt, iron, manganese, and nickel.

[0015] [6] A multilayer container described in any one of [1] to [5], wherein the yellowing inhibitor (A) is an anthraquinone dye.

[0016] [7] A multilayer container described in any one of [1] to [6], wherein the polyamide layer further comprises a greening inhibitor (C).

[0017] [8] A multilayer container described in [7], wherein the greening inhibitor (C) is at least one selected from the group consisting of anthraquinone dyes and azo dyes.

[0018] [9] A multilayer container described in any one of [1] to [8], wherein the polyamide layer further comprises a polyester resin (Z).

[0019]

[10] A multilayer container described in [9], wherein the content of polyester resin (Z) in the polyamide layer is 5 to 70 mass%.

[0020]

[11] A multilayer container described in any one of [1] to

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

[0021]

[12] A multilayer container having a 2 to 5-layer structure, wherein the outermost layer is a polyester layer, as described in any one of [1] to

[11] .

[0022]

[13] A multilayer container having a 3 to 5-layer structure, wherein the outermost layer and the innermost layer are polyester layers, as described in any one of [1] to

[12] above.

[0023]

[14] A method for manufacturing a multilayer container having a polyester layer containing a polyester resin (X) and a polyamide layer containing a polyamide resin (Y), a yellowing inhibitor (A), and an oxidation accelerator (B), wherein the content of the polyamide resin (Y) is 0.05 to 7.0 mass% relative to the total amount of the polyamide layer and the total polyester layer, the yellowing inhibitor (A) is a dye, and the content of the yellowing inhibitor (A) is 1 to 30 ppm relative to the total amount of the polyamide layer and the total polyester layer, comprising: a process 1 of preparing a polyamide resin mixture by mixing the polyamide resin (Y), the yellowing inhibitor (A), and the oxidation accelerator (B); a process 2 of obtaining a multilayer preform by co-injection molding the polyamide resin mixture and the polyester resin composition containing the polyester resin (X); and the multilayer preform A method for manufacturing a multilayer container comprising a blow molding process 3.

[0024]

[15] A method for manufacturing a multilayer container as described in

[14] , wherein, in process 1, a greening inhibitor (C) is additionally mixed.

[0025]

[16] A method for manufacturing a multilayer container as described in

[14] or

[15] , wherein, in process 1, a polyester resin (Z) is additionally mixed.

[0026]

[17] A method for manufacturing a multilayer container as described in any one of

[14] to

[16] , wherein in process 1, a polyamide resin or polyester resin, a yellowing inhibitor (A) and an oxidation promoter (B) are kneaded and then mixed with a polyamide resin (Y).

[0027]

[18] A method for manufacturing a multilayer container as described in any one of

[14] to

[17] , wherein the oxidation promoter (B) is a compound containing a transition metal.

[0028]

[19] A method for manufacturing a multilayer container as described in

[18] , wherein the transition metal is at least one selected from the group consisting of cobalt, iron, manganese, and nickel.

[0029]

[20] A method for manufacturing a multilayer container as described in any one of

[14] to

[19] , wherein the yellowing inhibitor (A) is an anthraquinone dye.

[0030]

[21] A method for manufacturing a multilayer container as described in any one of

[15] to

[20] , wherein the greening inhibitor (C) is at least one selected from the group consisting of anthraquinone dyes and azo dyes.

[0031]

[22] A method for manufacturing recycled polyester having a process for recovering polyester from a multilayer container described in any one of [1] to

[13] above.

[0032]

[23] A method for producing recycled polyester described in

[22] , comprising a process of removing all or part of the polyamide layer from a multilayer container to recover the polyester.

[0033]

[24] A method for producing recycled polyester described in

[22] or

[23] , wherein the removal of the polyamide layer is performed by balloon separation after crushing the multilayer container.

[0034]

[25] A method for producing recycled polyester as described in any one of

[22] to

[24] , wherein, after a process of recovering polyester, one or more processes selected from a crystallization process and a solid-state polymerization process are performed. Effects of the invention

[0035] According to the present invention, a multilayer container with excellent oxygen barrier properties capable of suppressing yellowing of recycled polyester during recycling, and a method for manufacturing recycled polyester with suppressed yellowing can be provided. Specific details for implementing the invention

[0036] [Multilayer Container]

[0037] The multilayer container of the present invention has a polyester layer comprising a polyester resin (X) and a polyamide layer comprising a polyamide resin (Y), a yellowing inhibitor (A) and an oxidation promoter (B), wherein the content of the polyamide resin (Y) is 0.05 to 7.0 mass% relative to the total amount of the polyamide layer and the total polyester layer, the yellowing inhibitor (A) is a dye, and the content of the yellowing inhibitor (A) is 1 to 30 ppm relative to the total amount of the polyamide layer and the total polyester layer.

[0038] The reason why the multilayer container of the present invention can achieve both oxygen barrier properties and inhibition of yellowing of regenerated polyester is not precise, but is thought to be as follows.

[0039] It is believed that the oxygen barrier layer is formed by the polyamide resin, and since an oxidation promoter additionally contributes to oxygen absorption, the oxygen barrier properties can be enhanced, and the dye has a stable structure, and since a small amount of yellowing inhibitor efficiently suppresses the yellowing of the regenerated polyester without hindering the oxidation promoter's action, these are considered to be compatible.

[0040] "Total amount of all polyamide layers and all polyester layers" refers to the total mass of all polyamide layers and all polyester layers constituting the multilayer container, and in cases where multiple layers exist, it refers to the total amount of all of them.

[0041] Polyester layer

[0042] The polyester layer includes polyester resin (X).

[0043] (Polyester resin(X))

[0044] 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 constituent unit derived from a dicarboxylic acid (dicarboxylic acid unit) and a constituent unit derived from a diol (diol unit).

[0045] Examples of dicarboxylic acid units include constituent units derived from aromatic dicarboxylic acids, constituent units derived from alicyclic dicarboxylic acids, and constituent units derived from aliphatic dicarboxylic acids, and constituent units derived from aromatic dicarboxylic acids are preferred.

[0046] Examples of aromatic dicarboxylic acids include terephthalic acid, isophthalic acid, orthophthalic acid, biphenyldicarboxylic acid, diphenylether-dicarboxylic acid, diphenylsulfone-dicarboxylic acid, diphenylketone-dicarboxylic acid, 2,6-naphthalenedicarboxylic acid, 1,4-naphthalenedicarboxylic acid, and 2,7-naphthalenedicarboxylic acid. In terms of cost and ease of manufacturing, 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. In terms of moldability, terephthalic acid and isophthalic acid are more preferred, and terephthalic acid is even more preferred.

[0047] Meanwhile, as an aromatic dicarboxylic acid, an alkyl ester of an aromatic dicarboxylic acid having 1 to 4 carbon atoms may also be used.

[0048] When recycling the multilayer container of the present invention, it may be melt-blended with a conventional single-layer container made of polyester resin. By having a unit derived from terephthalic acid as the dicarboxylic acid unit, the compatibility between the multilayer container of the present invention and the conventional single-layer container is improved, and good recyclability is obtained.

[0049] As an aromatic dicarboxylic acid, sulfophthalic acid or metal salts of sulfophthalic acid may be used. Metal salts of sulfophthalic acid are metal salts of sulfophthalic acid, and examples of these metal atoms include alkali metals and alkaline earth metals.

[0050] Specifically, sulfophthalic acid or sulfophthalic acid metal salt is represented by the following formula (I) or (I'), respectively.

[0051] [Chemical Formula 1]

[0052]

[0053] In the above equation (I'), M is a metal atom. n represents the valence of M.

[0054] Examples of metal atoms of M include alkali metals such as lithium, sodium, and potassium, and alkaline earth metals such as beryllium, magnesium, calcium, and strontium. Among these, alkali metals are preferred, sodium or lithium is preferred, and sodium is more preferred. Meanwhile, when n is 2 or more, it can be crosslinked with other units (for example, other sulfophthalic acid units or sulfo groups in sulfophthalic acid metal salt units) through M.

[0055] Among the above equations (I) and (I'), R A is a substituted or unsubstituted alkyl group, or a substituted or unsubstituted aryl group. m represents an integer from 0 to 3. Meanwhile, when m is 2 or 3, respectively R A It may be the same or different.

[0056] Examples of the above alkyl groups include methyl groups, ethyl groups, n-propyl groups, isopropyl groups, n-butyl groups, t-butyl groups, n-octyl groups, 2-ethylhexyl groups, etc. Among these, an alkyl group having 1 to 6 carbon atoms is preferred, and an alkyl group having 1 to 4 carbon atoms is more preferred.

[0057] Examples of the above aryl groups include phenyl groups, naphthyl groups, etc. Among these, an aryl group having 6 to 12 carbon atoms is preferred, and a phenyl group is more preferred.

[0058] Examples of substituents that the above alkyl and aryl groups may have include halogen atoms such as chlorine atoms, bromine atoms, and iodine atoms, alkyl groups, alkenyl groups, aryl groups, cyano groups, hydroxyl groups, nitro groups, alkoxy groups, aryloxy groups, acyl groups, amino groups, mercapto groups, alkylthio groups, arylthio groups, etc. Among these groups, those having a hydrogen atom may additionally be substituted by the substituents described above.

[0059] R A Specific examples include methyl group, ethyl group, n-propyl group, isopropyl group, n-butyl group, t-butyl group, 1-methylpropyl group, 2-methylpropyl group, hydroxymethyl group, 1-hydroxyethyl group, mercaptomethyl group, methylthioethyl group, phenyl group, naphthyl group, biphenyl group, benzyl group, and 4-hydroxybenzyl group, among which methyl group, ethyl group, and benzyl group are preferred.

[0060] Among the above equations (I) and (I'), R B represents a hydrogen atom, or an alkyl group having 1 to 4 carbon atoms.

[0061] Desirable R A As for this, as described above, the sulfophthalic acid or sulfophthalic acid metal salt used in the polyester resin (X) is m=0, i.e., the benzene ring is R A Units represented by the following formulas (Ia) or (I'a), respectively, which are not substituted by , are preferred.

[0062] [Chemical Formula 2]

[0063]

[0064] Among the above equation (Ia), R B is R in the above equation (I). B It is the same as.

[0065] In addition, among the above equation (I'a), R B , M, and n are R in the above equation (I'). B It is the same as , M, and n.

[0066] Furthermore, the sulfophthalic acid represented by the above formula (Ia) or the sulfophthalic acid metal salt represented by the above formula (I'a) may include a phthalic acid structure in which two -CO- groups are bonded at the ortho position, an isophthalic acid structure in which they are bonded at the meta position, and a terephthalic acid structure in which they are bonded at the para position, among which the isophthalic acid structure is preferred. That is, it is preferred to be at least one of the sulfoisophthalic acid represented by the following formula (Ib) and the sulfoisophthalic acid metal salt represented by the following formula (I'b).

[0067] [Chemical Formula 3]

[0068]

[0069] Among the above equation (Ib), R B is R in the above equation (I). B It is the same as.

[0070] Among the above equation (I'b), R B , M, and n are R in the above equation (I'). B It is the same as , M, and n.

[0071] The sulfo group in sulfoisophthalic acid or sulfoisophthalic acid metal salt can take positions 2, 4, 5, and 6, but it is preferable that it be substituted at position 5, represented by the following formula (Ic) or (I'c).

[0072] [Chemical Formula 4]

[0073]

[0074] Among the above equation (Ic), R B is R in the above equation (I). B It is the same as.

[0075] Among the above equation (I'c), R B , M and n are R in the above equation (I'). B It is the same as , M and n.

[0076] Among the polyester resin (X), the sulfoisophthalic acid or sulfoisophthalic acid metal salt represented by the above formula (Ic) or formula (I'c) may include, for example, 5-sulfoisophthalic acid, sodium 5-sulfoisophthalic acid, lithium 5-sulfoisophthalic acid, potassium 5-sulfoisophthalic acid, bis(5-sulfoisophthalic acid)calcium, dimethyl sodium 5-sulfoisophthalic acid, diethyl sodium 5-sulfoisophthalic acid, etc.

[0077] When a polyester resin (X) contains a constituent unit derived from at least one selected from the group consisting of sulfophthalic acid and sulfophthalic acid metal salts, it is preferable to contain at least a constituent unit derived from a sulfophthalic acid metal salt. The content of the constituent unit derived from sulfophthalic acid and sulfophthalic acid metal salts in the polyester resin is preferably 0.01 to 15 mol% of the total constituent unit derived from dicarboxylic acid, more preferably 0.03 to 10.0 mol%, even more preferably 0.06 to 5.0 mol%, and even more preferably 0.08 to 2.0 mol%.

[0078] Examples of dicarboxylic acids include cyclohexanedicarboxylic acid, norbornendicarboxylic acid, and tricyclodecanedicarboxylic acid.

[0079] Aliphatic dicarboxylic acids include malonic acid, succinic acid, adipic acid, azelaic acid, and sebacic acid.

[0080] As for diol units, constituent units derived from aliphatic diols, constituent units derived from alicyclic diols, and constituent units derived from aromatic diols may be included, and constituent units derived from aliphatic diols are preferred.

[0081] Examples of aliphatic diols include ethylene glycol, 2-butene-1,4-diol, trimethylene glycol, tetramethylene glycol, hexamethylene glycol, neopentyl glycol, methylpentanediol, and diethylene glycol. Among these, ethylene glycol is preferred.

[0082] Examples of cyclohexanedimethanol include cyclohexanedimethanol, isosorbide, spiroglycol, 2,2,4,4-tetramethyl-1,3-cyclobutanediol, norbornendimethanol, and tricyclodecanedimethanol.

[0083] Examples of aromatic diols include bisphenol compounds and hydroquinone compounds.

[0084] Polyester resin (X) may have constituent units derived from hydroxycarboxylic acid.

[0085] Examples of hydroxycarboxylic acids include aliphatic hydroxycarboxylic acids, alicyclic hydroxycarboxylic acids, and aromatic hydroxycarboxylic acids.

[0086] Examples of aliphatic hydroxycarboxylic acids include 10-hydroxyoctadecanoyl acid, lactic acid, hydroxyacrylic acid, 2-hydroxy-2-methylpropionic acid, and hydroxybutyric acid.

[0087] Examples of cyclocyclic hydroxycarboxylic acids include hydroxymethylcyclohexanecarboxylic acid, hydroxymethylnorbornenecarboxylic acid, and hydroxymethyltricyclodecanecarboxylic acid.

[0088] Examples of aromatic hydroxycarboxylic acids include hydroxyanoxic acid, hydroxytoluic acid, hydroxynaphthoic acid, 3-(hydroxyphenyl)propionic acid, hydroxyphenylacetic acid, and 3-hydroxy-3-phenylpropionic acid.

[0089] The polyester resin (X) may have constituent units derived from monofunctional compounds and constituent units derived from polyfunctional compounds.

[0090] Examples of monofunctional compounds include monocarboxylic acids and monoalcohols, and specifically, aromatic monocarboxylic acids, aliphatic monocarboxylic acids, aromatic monoalcohols, aliphatic monoalcohols, alicyclic monoalcohols, etc.

[0091] Examples of polyfunctional compounds include aromatic polycarboxylic acids, alicyclic polycarboxylic acids, aliphatic polyalcohols, alicyclic polyalcohols, and their esters.

[0092] The polyester resin (X) preferably has a constituent unit derived from a dicarboxylic acid containing a constituent unit derived from terephthalic acid and a constituent unit derived from a diol containing a constituent unit derived from ethylene glycol, more preferably has a constituent unit derived from a dicarboxylic acid containing 80 mol% or more of a constituent unit derived from terephthalic acid and a constituent unit derived from a diol containing 80 mol% or more of a constituent unit derived from ethylene glycol, even more preferably has a constituent unit derived from a dicarboxylic acid containing 90 mol% or more of a constituent unit derived from terephthalic acid and a constituent unit derived from a diol containing 90 mol% or more of a constituent unit derived from ethylene glycol, and even more preferably has a constituent unit derived from a dicarboxylic acid containing 98 mol% or more of a constituent unit derived from terephthalic acid and a constituent unit derived from a diol containing substantially 100 mol% of a constituent unit derived from ethylene glycol.

[0093] Specific examples of polyester resin (X) include polyethylene terephthalate (PET).

[0094] Polyethylene terephthalate (PET) may include constituent units derived from aromatic dicarboxylic acids other than terephthalic acid. As aromatic dicarboxylic acids other than terephthalic acid, it is preferable that one or more are selected from isophthalic acid, orthophthalic acid, naphthalenedicarboxylic acid, and 4,4'-biphenyldicarboxylic acid. These have low costs, and copolymerized polyester resins containing them are easy to manufacture.

[0095] Among these, isophthalic acid and naphthalene dicarboxylic acid are preferred, and isophthalic acid is more preferred. Polyethylene terephthalate containing constituent units derived from isophthalic acid is excellent in that it has excellent moldability and also prevents whitening of the molded product by slowing down the crystallization rate. In addition, polyethylene terephthalate containing constituent units derived from naphthalene dicarboxylic acid raises the glass transition point of the resin, improves heat resistance, and absorbs ultraviolet rays, making it suitable for use in the manufacture of multilayer containers that require resistance to ultraviolet rays. Meanwhile, regarding naphthalene dicarboxylic acid, the 2,6-naphthalene dicarboxylic acid component is preferred in that it is easy to manufacture and highly economical.

[0096] When polyethylene terephthalate contains constituent units derived from aromatic dicarboxylic acids other than terephthalic acid, the proportion of the composition derived from aromatic dicarboxylic acids other than terephthalic acid is preferably 1 to 20 mol% of the dicarboxylic acid units, more preferably 1 to 10 mol%, and even more preferably 1 to 5 mol%.

[0097] Among these, when polyethylene terephthalate contains constituent units derived from isophthalic acid, the proportion of the isophthalic acid-derived composition is preferably 1 to 20 mol% of the dicarboxylic acid units, more preferably 1 to 10 mol%, and even more preferably 1 to 5 mol%.

[0098] Meanwhile, the polyester resin (X) may be used as a single type or two or more types of resins may be used in combination.

[0099] Polyester resin (X) can be manufactured by a known method, such as direct esterification or ester exchange.

[0100] 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. If the intrinsic viscosity is 0.5 dL / g or higher, the mechanical properties of the container are excellent.

[0101] Meanwhile, the intrinsic viscosity is prepared by dissolving the polyester resin in a mixed solvent of phenol / 1,1,2,2-tetrachloroethane (=6 / 4 mass ratio) to prepare solutions of 0.2, 0.4, and 0.6 g / dL, and is measured at 25°C using an automatic viscosity measuring device (Malburn, Viscotek).

[0102] (Other ingredients)

[0103] The polyester layer may contain other components. Examples of other components include heat stabilizers, light stabilizers, moisture-proofing agents, waterproofing agents, lubricants, and electrodeposition agents.

[0104] The polyester layer may contain a resin other than the main component polyester resin (X) to the extent that it does not impair the effects of the present invention. The content of the polyester resin (X) is preferably 80 to 100 mass%, more preferably 90 to 100 mass%, with respect to the total amount of resin in the polyester layer.

[0105] Polyamide layer

[0106] The polyamide layer comprises a polyamide resin (Y), a yellowing inhibitor (A), and an oxidation promoter (B). Additionally, the content of the polyamide resin (Y) included in the polyamide layer is 0.05 to 7.0 mass% relative to the total amount of the polyamide layer and the total polyester layer, the yellowing inhibitor (A) is a dye, and the content of the yellowing inhibitor (A) is 1 to 30 ppm relative to the total amount of the polyamide layer and the total polyester layer.

[0107] By providing a polyamide layer, the multilayer container has high oxygen barrier properties. In the present invention, by additionally including an oxidation promoter (B) and a yellowing inhibitor (A), which is a dye, in the polyamide layer, it is possible to achieve both very high oxygen barrier properties and yellowing inhibition of the recycled polyester produced from the multilayer container.

[0108] The reason for this excellent effect is not certain, but it is thought to be as follows.

[0109] In the present invention, yellowing can be effectively suppressed by including a yellowing inhibitor (A) in a nitrogen-containing polyamide layer that is prone to causing yellowing of recycled resin. However, if these yellowing inhibitors are coexisted with an oxidation promoter, oxygen absorption by the oxidation promoter is inhibited. In the present invention, it is believed that by using a specific amount of a dye that is difficult to inhibit oxidation reactions as a yellowing inhibitor and including it in the polyamide layer together with an oxidation promoter, effective yellowing inhibition performance can be achieved while increasing oxygen absorption capacity.

[0110] (Polyamide resin(Y))

[0111] Examples of polyamide resins (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 easy to separate from the polyester layer during recycling. The xylylene group-containing polyamide resin is preferably a polyamide resin containing constituent units derived from xylylenediamine.

[0112] A xylylene group-containing polyamide resin is obtained by polycondensing a diamine containing xylylenediamine with a dicarboxylic acid, and has a constituent unit derived from xylylenediamine and a constituent unit derived from a dicarboxylic acid. Among the constituent units (diamine units) derived from the diamine, it is preferable for the xylylene group-containing polyamide resin to have 50 mol% or more of a constituent unit derived from xylylenediamine, more preferable to have 70 mol% or more, even more preferable to have 80 to 100 mol%, and even more preferable to have 90 to 100 mol%.

[0113] Xylylenediamine is preferably metaxylylenediamine, paraxylylenediamine, or both, but metaxylylenediamine is more preferable. Furthermore, the diamine units constituting the xylylene group-containing polyamide resin preferably contain 50 mol% or more of constituent units derived from metaxylylenediamine, more preferably 70 mol% or more, even more preferably 80 to 100 mol%, and even more preferably 90 to 100 mol%. By ensuring that the constituent units derived from metaxylylenediamine among the diamine units are within the above range, the gas barrier properties of the polyamide resin are improved.

[0114] The diamine unit in the xylylene group-containing polyamide resin may consist solely of a constituent unit derived from xylylenediamine, or it may contain a constituent unit derived from a diamine other than xylylenediamine. Here, the diamine other than xylylenediamine includes aliphatic diamines having a straight-chain 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; Examples include alicyclic diamines such as 1,3-bis(aminomethyl)cyclohexane, 1,4-bis(aminomethyl)cyclohexane, 1,3-diaminocyclohexane, 1,4-diaminocyclohexane, bis(4-aminocyclohexyl)methane, 2,2-bis(4-aminocyclohexyl)propane, bis(aminomethyl)decalin, bis(aminomethyl)tricyclodecane, etc., and diamines having an aromatic ring such as bis(4-aminophenyl)ether, paraphenylenediamine, and bis(aminomethyl)naphthalene.

[0115] In a polyamide resin containing xylylene groups, compounds capable of constituting a dicarboxylic acid unit include α,ω-linear aliphatic dicarboxylic acids having 4 to 20 carbon atoms, such as succinic acid, glutaric acid, adipic acid, pimelolic acid, souveric acid, azelaic acid, sebacic acid, undecanic acid, and dodecaneic acid; alicyclic dicarboxylic acids such as 1,4-cyclohexanedicarboxylic acid; other aliphatic dicarboxylic acids such as dimer acid; aromatic dicarboxylic acids such as terephthalic acid, isophthalic acid, orthophthalic acid, xylylenedicarboxylic acid, and naphthalenedicarboxylic acid, and α,ω-linear aliphatic dicarboxylic acids having 4 to 20 carbon atoms are preferred, adipic acid and sebacic acid are more preferred, and adipic acid is even more preferred from the perspective of improving barrier performance.

[0116] The xylylene group-containing polyamide resin preferably contains 50 mol% or more of a dicarboxylic acid-derived constituent units among the dicarboxylic acid-derived constituent units (dicarboxylic acid units), more preferably contains 70 mol% or more, even more preferably contains 80 to 100 mol%, and even more preferably contains 90 to 100 mol%.

[0117] That is, the polyamide resin (Y) preferably has a constituent unit derived from a diamine containing 50 mol% or more of a constituent unit derived from xylylenediamine and a constituent unit derived from a dicarboxylic acid containing 50 mol% or more of a constituent unit derived from adipic acid, and more preferably has a constituent unit derived from a diamine containing 80 mol% or more of a constituent unit derived from xylylenediamine and a constituent unit derived from a dicarboxylic acid containing 80 mol% or more of a constituent unit derived from adipic acid.

[0118] As for xylylendiamine, metaxylylendiamine is preferred.

[0119] In addition, for the remaining dicarboxylic acid units excluding adipic acid, constituent units derived from α,ω-linear aliphatic dicarboxylic acids having 4 to 20 carbon atoms are preferred.

[0120] In addition, a preferred polyamide resin containing xylylene groups may be exemplified as a polyamide resin in which at least 70 mol% of the diamine units are derived from xylylenediamine (preferably metaxylylenediamine), 70 to 99 mol% of the dicarboxylic acid units are derived from adipic acid, and 1 to 30 mol% are derived from isophthalic acid. The polyamide resin is preferably a polyamide resin in which at least 80 mol% of the diamine units are derived from metaxylylenediamine (preferably metaxylylenediamine), 80 to 99 mol% of the dicarboxylic acid units are derived from adipic acid, and 1 to 20 mol% are derived from isophthalic acid.

[0121] By adding isophthalic acid units as dicarboxylic acid units, the melting point is lowered and the molding processing temperature can be lowered, thereby suppressing thermal degradation during molding, and also, by delaying the crystallization time, the elongation formability is improved.

[0122] In addition to the above-mentioned diamines and dicarboxylic acids, as components constituting the xylylene group-containing polyamide resin, within a range that does not impair the effects of the present invention, lactams such as ε-caprolactam or laurolactam, aliphatic aminocarboxylic acids such as aminocaproic acid and aminoundecanic acid; and aromatic aminocarboxylic acids such as p-aminomethylbenzoic acid may also be used as copolymerization components.

[0123] It is preferable to manufacture xylylene group-containing polyamide resins by a polycondensation reaction in a molten state (hereinafter also referred to as "melt polycondensation"). For example, it is preferable to manufacture them by a method in which a nylon salt composed of a diamine and a dicarboxylic acid is heated by a pressurized method in the presence of water and polymerized in a molten state while removing the water. Alternatively, they may be manufactured by a method in which a diamine is directly added to a molten dicarboxylic acid and polycondensed under atmospheric pressure. In this case, in order to maintain the reaction system in a homogeneous liquid state, it is preferable to continuously add the diamine to the dicarboxylic acid and, while doing so, proceed with the polycondensation by heating the reaction system so that the reaction temperature does not fall below the melting point of the oligoamide and polyamide produced. Additionally, the molecular weight of the xylylene group-containing polyamide may be increased by further solid-state polymerization of the material obtained by melt polycondensation, if necessary.

[0124] It is preferable to polycondense the xylylene group-containing polyamide resin in the presence of a single-cell containing compound. When the xylylene group-containing polyamide resin is polycondensed in the presence of a single-cell containing compound, the processing stability during melt molding is enhanced, and discoloration becomes easier to suppress.

[0125] As for the phosphorus-containing compounds, hypophosphoric acid compounds and phosphoric acid compounds are preferred, and hypophosphoric acid compounds are more preferred.

[0126] The compound containing the phosphate group is preferably an organometallic salt, and among them, an alkali metal salt is more preferable.

[0127] Examples of hypophosphoric acid compounds include hypophosphoric acid, metal hypophosphoric acid salts, metal phenylaphosphonic acid salts, ethyl hypophosphoric acid, dimethylphosphinic acid, phenylmethylphosphinic acid, phenylaphosphonic acid, and ethyl phenylaphosphonic acid, in terms of promoting polymerization reactions and preventing discoloration, and metal hypophosphoric acid salts are preferred.

[0128] Examples of metal hypophosphorus salts include sodium hypophosphorus, potassium hypophosphorus, lithium hypophosphorus, and calcium hypophosphorus, and sodium hypophosphorus is more preferable.

[0129] Examples of metal salts of phenylaphosphonic acid include sodium phenylaphosphonic acid, potassium phenylaphosphonic acid, and lithium phenylaphosphonic acid.

[0130] Examples of phosphoric acid compounds include phosphoric acid, pyrophosphoric acid, metal phosphoric acid salts, metal phenylphosphonic acid salts, triethyl phosphoric acid, triphenyl phosphoric acid, ethylphosphonic acid, phenylphosphonic acid, and diethyl phenylphosphonic acid.

[0131] Examples of metal phosphate salts include sodium biphosphate, sodium phosphate, potassium phosphate, and calcium phosphate.

[0132] Examples of metal phenylphosphonic acid salts include sodium ethylphosphonate, potassium ethylphosphonate, sodium phenylphosphonate, potassium phenylphosphonate, lithium phenylphosphonate, etc.

[0133] The compound containing the phosphate group may be of one type, or two or more types may be used in combination.

[0134] In addition, it is preferable to perform the polycondensation of the xylylene group-containing polyamide resin in the presence of a single-cell-containing compound and an alkali metal compound. If the amount of single-cell-containing compound used is excessive, there is a risk that the polyamide resin will gel. Therefore, it is preferable to coexist with an alkali metal compound from the perspective of controlling the amidation reaction rate.

[0135] Examples of alkali metal compounds include alkali metal hydroxides and alkali metal acetates. Examples of alkali metal hydroxides include lithium hydroxide, sodium hydroxide, potassium hydroxide, rubidium hydroxide, and cesium hydroxide, and examples of alkali metal acetates include lithium acetate, sodium acetate, potassium acetate, rubidium acetate, and cesium acetate.

[0136] When using an alkali metal compound when polycondensing a polyamide resin, the amount of alkali metal compound used is, from the perspective of suppressing gel formation, a value obtained by dividing the number of moles of the alkali metal compound by the number of moles of the phosphine-containing compound is preferably 0.5 to 1, more preferably 0.55 to 0.95, and even more preferably 0.6 to 0.9.

[0137] The number average molecular weight of the polyamide resin is appropriately selected according to the use or molding method of the multilayer container, and from the perspective of moldability or strength of the multilayer container, 10,000 to 60,000 is preferred, and 11,000 to 50,000 is more preferred.

[0138] Meanwhile, the number average molecular weight of the polyamide resin is calculated from the following equation (X).

[0139] Number average molecular weight = 2 × 1,000,000 / ([COOH] + [NH2])····(X)

[0140] (In the formula, [COOH] represents the terminal carboxyl group concentration (μmol / g) in the polyamide resin, and [NH2] represents the terminal amino group concentration (μmol / g) in the polyamide resin.)

[0141] Here, the terminal amino group concentration is calculated by neutralizing the polyamide resin dissolved in a phenol / ethanol mixed solution with a dilute hydrochloric acid aqueous solution, and the terminal carboxyl group concentration is calculated by neutralizing the polyamide dissolved in benzyl alcohol with a sodium hydroxide aqueous solution.

[0142] The content of polyamide resin (Y) included in the polyamide layer is 0.05 to 7.0 mass% with respect to the total amount of the polyamide layer and the total polyester layer, and from the perspective of gas barrier properties and inhibition of yellowing of recycled polyester, 0.5 to 6.0 mass% is preferred, 1.0 to 5.0 mass% is more preferred, and 1.5 to 4.5 mass% is even more preferred.

[0143] (Yellowing inhibitor(A))

[0144] The polyamide layer of the multilayer container contains a yellowing inhibitor (A), and the yellowing inhibitor (A) is a dye, and its content is 1 to 30 ppm relative to the total amount of the polyamide layer and the total polyester layer.

[0145] The content of the yellowing inhibitor (A) is 1 to 30 ppm with respect to the total amount of the polyamide layer and the total polyester layer, and 1.5 to 25 ppm is preferred from the perspective of effectively suppressing yellowing of the recycled polyester, 2 to 22 ppm is more preferred from the perspective of mixability and moldability during manufacturing, 3 to 20 ppm is even more preferred, and 8 to 20 ppm is even more preferred.

[0146] Meanwhile, in the present invention, "ppm" refers to parts per million by mass.

[0147] The content of the yellowing inhibitor (A) is preferably 0.001 to 1.0 mass% in the polyamide layer, more preferably 0.005 to 0.5 mass%, even more preferably 0.008 to 0.1 mass%, even more preferably 0.01 to 0.08 mass%, and even more preferably 0.03 to 0.08 mass%, in order to effectively inhibit yellowing of the recycled polyester.

[0148] The yellowing inhibitor (A) is a dye in terms of transparency, and among them, a blue dye is preferred.

[0149] By using a dye, yellowing of the recycled polyester obtained from the multilayer container of the present invention can be suppressed in extremely small amounts. In addition, recycled polyester with excellent transparency can be obtained.

[0150] Here, "dye" refers to a coloring agent soluble in a solvent.

[0151] Examples of dyes include anthraquinone dyes, pyrazolone dyes, coumarin dyes, perinone dyes, methine dyes, and quinophthalone dyes, and anthraquinone dyes are preferred.

[0152] Examples of anthraquinone dyes include anthraquinone dyes in which the hydrogen atoms of the aromatic ring are substituted with aromatic amines, aliphatic amines, and halogens, and anthraquinone dyes in which the hydrogen atoms of the aromatic ring are substituted with aromatic amines are preferred. By using such anthraquinone dyes, yellowing of the regenerated polyester can be suppressed. As for anthraquinone dyes, anthraquinone dyes in which the hydrogen atoms of the aromatic ring are not substituted with hydroxyl groups are preferred. By using such anthraquinone dyes, high oxygen barrier properties are obtained in the multilayer container of the present invention.

[0153] By using an anthraquinone-based dye, yellowing of the regenerated polyester obtained from the multilayer container of the present invention can be suppressed in extremely small amounts.

[0154] Among anthraquinone dyes, it is more preferable to use an anthraquinone blue dye.

[0155] As an anthraquinone dye, a compound represented by the following formula (1) is preferred.

[0156] [Chemical Formula 5]

[0157]

[0158] (In the formula, n represents the number of R groups, and the two n groups are each independently 1 to 5. The 2n R groups each independently represent an alkyl group having 1 to 4 carbon atoms.)

[0159] In formula (1), n ​​is 1 to 5, preferably 2 to 5, and more preferably 2 to 3. By setting n to the above range, the yellowing (Δb) of the regenerated polyester * The value) can be suppressed. It is preferable that R each independently represents an alkyl group having 1 to 4 carbon atoms and is at least one selected from the group consisting of methyl and ethyl groups. It is preferable that R substitutes at least an ortho position or a para position with respect to the amino group, it is preferable that it substitutes at least a para position, it is more preferable that it substitutes at least an ortho position, and it is even more preferable that it substitutes both an ortho position and a para position.

[0160] Specific compounds represented by formula (1) include 1,4-bis[(2-ethyl-6-methylphenyl)amino]anthraquinone, Solvent Blue 97, Solvent Blue 104, and Solvent Green 3, and 1,4-bis[(2-ethyl-6-methylphenyl)amino]anthraquinone, Solvent Blue 97, and Solvent Blue 104 are preferred.

[0161] Commercially available yellowing inhibitors (A) include MACROLEX Blue 3R (1,4-bis[(2-ethyl-6-methylphenyl)amino]anthraquinone, anthraquinone dye, manufactured by LANXESS), MACROLEX Blue RR Gran (anthraquinone dye, manufactured by LANXESS), Oracet Blue 690 (anthraquinone dye, manufactured by BASF), Quinizarin Green SS (anthraquinone dye, manufactured by Tokyo Kasei Kogyo), etc.

[0162] (Oxidation promoter(B))

[0163] In the multilayer container of the present invention, for the purpose of inducing an oxidation reaction of the polyamide resin (Y) to increase the oxygen absorption function and further increase the gas barrier properties, the polyamide layer includes an oxidation promoter (B).

[0164] The oxidation promoter (B) is preferably a compound containing a transition metal, and more preferably at least one selected from the group consisting of transition metal elements, oxides, inorganic salts, organic salts, and complexes.

[0165] Examples of inorganic salts include halides such as chlorides and bromides, carbonates, sulfates, nitrates, phosphates, and silicates.

[0166] Examples of organic acid salts include carboxylates, sulfonates, and phosphonates.

[0167] Examples of complexes include complexes with β-diketones or β-keto acid esters.

[0168] As for the above transition metal, a transition metal of Group VIII of the periodic table is preferred, and from the view of exhibiting oxygen absorption ability, at least one selected from the group consisting of cobalt, iron, manganese, and nickel is more preferred, and cobalt is even more preferred.

[0169] In terms of exhibiting good oxygen absorption capacity, among compounds containing transition metals, specifically, at least one selected from the group consisting of carboxylates, carbonates, acetylacetonate complexes, oxides, and halides containing transition metals is preferred, at least one selected from octanoates, neodecanoates, naphthenates, stearates, acetates, carbonates, and acetylacetonate complexes is more preferred, and cobalt carboxylates such as cobalt octanoate, cobalt naphthenate, cobalt acetate, cobalt neodecanoate, and cobalt stearate are even more preferred.

[0170] Oxidation promoter (B) may be used as a single type or in combination of two or more types.

[0171] The content of the oxidation promoter (B) is preferably 0.0001 to 1.0 mass% with respect to the polyamide layer, more preferably 0.01 to 0.8 mass%, and even more preferably 0.05 to 0.6 mass%, in order to increase gas barrier properties and also suppress yellowing of the recycled polyester resin.

[0172] In addition, the content of the oxidation promoter (B) is preferably 0.0001 to 1.0 parts by mass, more preferably 0.01 to 0.8 parts by mass, and even more preferably 0.05 to 0.6 parts by mass, with respect to increasing gas barrier properties and suppressing yellowing of the recycled polyester resin.

[0173] Furthermore, the content of the transition metal of the oxidation promoter (B) is preferably 0.00001 to 0.1 mass% with respect to the polyamide layer, more preferably 0.0001 to 0.08 mass%, and even more preferably 0.0003 to 0.06 mass%, in order to increase gas barrier properties and also suppress yellowing of the recycled polyester resin.

[0174] In addition, the content of the transition metal in the oxidation promoter (B) is preferably 0.00001 to 0.1 parts by mass, more preferably 0.0001 to 0.08 parts by mass, and even more preferably 0.0003 to 0.06 parts by mass, with respect to increasing gas barrier properties and suppressing yellowing of the recycled polyester resin, with respect to 100 parts by mass of polyamide resin (Y). Meanwhile, when a carboxylate containing a transition metal is used as the oxidation promoter (B), the content of the transition metal refers to the content of the transition metal itself in the compound containing the said transition metal.

[0175] (Green stool inhibitor(C))

[0176] The polyamide layer of the multilayer container preferably includes a greening inhibitor (C).

[0177] The greening inhibitor (C) is -a when measured with a colorimeter when the multilayer container of the present invention is recycled into recycled polyester. * Suppresses the green of the direction.

[0178] The content of the greening inhibitor (C) is 1 to 30 ppm with respect to the total amount of the polyamide layer and the total polyester layer, and 1.5 to 25 ppm is preferred from the perspective of effectively inhibiting greening of the recycled polyester, 2 to 22 ppm is more preferred from the perspective of mixability and moldability during manufacturing, and 3 to 20 ppm is even more preferred.

[0179] Meanwhile, in the present invention, "ppm" refers to parts per million by mass.

[0180] The content of the greening inhibitor (C) is preferably 0.001 to 1.0 mass% in the polyamide layer, more preferably 0.005 to 0.5 mass%, even more preferably 0.008 to 0.1 mass%, and even more preferably 0.01 to 0.08 mass%, in order to effectively inhibit greening of the recycled polyester.

[0181] In the polyamide layer of the multilayer container of the present invention, the mass ratio [(A) / (C)] of the yellowing inhibitor (A) and the greening inhibitor (C) is preferably 20 / 80 to 80 / 20, more preferably 30 / 70 to 70 / 30, and even more preferably 40 / 60 to 60 / 40.

[0182] If the above mass ratio is within this range, the color change of the recycled polyester obtained after recycling is reduced, and a polyester with particularly excellent colorlessness is obtained.

[0183] The greening inhibitor (C) is preferably a dye in terms of transparency.

[0184] Among the dyes, it is preferable to select at least one from the group consisting of anthraquinone dyes and azo dyes, and from the perspective of heat resistance, anthraquinone dyes are more preferable.

[0185] Here, "dye" refers to a coloring agent soluble in a solvent.

[0186] As for the anthraquinone dye, an anthraquinone dye in which the hydrogen atom of the aromatic ring is not substituted with a hydroxyl group is preferred. By using such an anthraquinone dye, high oxygen gas barrier properties are obtained in the multilayer container of the present invention.

[0187] In addition, the greening inhibitor (C) is preferably a red dye, more preferably at least one selected from the group consisting of anthraquinone-based red dyes and azo-based red dyes, and anthraquinone-based red dyes are even more preferable from the perspective of heat resistance.

[0188] By using anthraquinone-based red dyes and azo-based red dyes, the greening of the regenerated polyester obtained from the multilayer container of the present invention can be suppressed in extremely small amounts.

[0189] As an anthraquinone dye, a compound represented by the following formula (2) is preferred.

[0190] [Chemical Formula 6]

[0191]

[0192] (In Equation (2), each of the two Ys independently represents a hydrogen atom or a group represented by Equation (2a). However, at least one Y is a group represented by Equation (2a).

[0193] In formula (2a), R represents an alkyl group having 1 to 4 carbon atoms.

[0194] In formula (2), the two Ys each independently represent a hydrogen atom or a group represented by formula (2a), at least one Y is a group represented by formula (2a), and it is preferable that one Y is a group represented by formula (2a) and the remaining Y is a hydrogen atom.

[0195] In formula (2a), R represents an alkyl group having 1 to 4 carbon atoms and is preferably at least one selected from the group consisting of methyl and ethyl groups. Meanwhile, when two Ys are groups represented by formula (2a), the Rs in the two groups represented by formula (2a) may be the same or different. It is preferable that R substitutes a para position with respect to an amino group.

[0196] Specific compounds represented by formula (2) include Solvent Violet 36, etc.

[0197] The greening inhibitor (B) may be used as a single type or in combination with two or more types.

[0198] Commercially available products of greening inhibitors (B) include MACROLEX Violet 3R Gran (anthraquinone dye, manufactured by LANXESS), MACROLEX Red Violet R Gran (Disperse Violet 31, Disperse Violet 26, Solvent Violet 59, anthraquinone dye, manufactured by LANXESS), MACROLEX Red 5B Gran (Disperse Violet 31, Disperse Violet 26, Solvent Violet 59, anthraquinone dye, manufactured by LANXESS), and MACROLEX Red B (Solvent Red 195, azo dye, manufactured by LANXESS).

[0199] (Polyester resin(Z))

[0200] The polyamide layer of the multilayer container preferably includes a polyester resin (Z) in order to suppress yellowing of the recycled polyester and improve impact resistance.

[0201] The polyester resin (Z) used in the polyamide layer is preferably the polyester resin described in the section on (polyester resin (X)) included in the polyester layer, and any suitable polyester resin is the same.

[0202] Specifically, the polyester resin (Z) is preferably polyethylene terephthalate (PET). The polyethylene terephthalate may include a constituent unit derived from an aromatic dicarboxylic acid other than terephthalic acid, and the constituent unit derived from an aromatic dicarboxylic acid other than terephthalic acid is preferably a constituent unit derived from sulfophthalic acid or a metal salt of sulfophthalic acid. The metal salt of sulfophthalic acid is a metal salt of sulfophthalic acid, and examples of this metal atom include alkali metals and alkaline earth metals.

[0203] By including polyester resin (Z) in the polyamide layer, the yellowing of the recycled polyester obtained by recycling is suppressed, and the adhesion between the polyamide layer and the polyester layer is improved, which is why the impact resistance of the multilayer container is improved.

[0204] (Other ingredients)

[0205] The polyamide layer may contain other components. Examples of other components include heat stabilizers, light stabilizers, moisture-proofing agents, waterproofing agents, lubricants, electrodeposition agents, etc.

[0206] The polyamide layer may contain a resin other than the main component polyamide resin (Y) to the extent that it does not impair the effects of the present invention.

[0207] In particular, when mixing a yellowing inhibitor (A) using the masterbatch method described below, it is preferable to include a polyamide resin or polyester resin used in the masterbatch. In that case, the polyamide resin or polyester resin used in the masterbatch is preferably 1 to 20 mass% and more preferably 3 to 15 mass% with respect to the total resin amount of the polyamide layer.

[0208] (Resin composition in the polyamide layer)

[0209] The content of polyamide resin (Y) in the polyamide layer is preferably 80 to 100 mass% with respect to the total resin amount of the polyamide layer from the perspective of gas barrier properties, and more preferably 90 to 100 mass%.

[0210] In addition, when a polyester resin (Z) is included in the polyamide layer, the content of the polyester resin (Z) in the polyamide layer is preferably 5 to 70 mass%, more preferably 10 to 65 mass%, even more preferably 20 to 65 mass%, and even more preferably 40 to 65 mass% from the perspective of impact resistance and gas barrier properties. When the content of the polyester resin (Z) is within the above range, the multilayer container of the present invention suppresses yellowing of the recycled polyester obtained by recycling, and at the same time, the adhesion between the polyamide layer and the polyester layer is improved, and the impact resistance is good.

[0211] Structure and Characteristics of Multilayer Containers

[0212] The multilayer container of the present invention has a multilayer structure comprising a polyester layer containing a polyester resin (X) and a polyamide layer containing a polyamide resin (Y), a yellowing inhibitor (A) and an oxidation promoter (B).

[0213] The multilayer container of the present invention may include a resin layer other than the polyester layer and the polyamide layer. From the perspective of facilitating separation during recycling and improving the yellowing inhibition effect, it is preferable that the content of the resin layer other than the polyester layer and the polyamide layer be low, and it is preferable that the resin layer other than the polyester layer and the polyamide layer be substantially not included. Additionally, an adhesive layer made of an adhesive or an inorganic layer made of an inorganic material may be provided. Regarding these as well, from the perspective of facilitating separation during recycling and improving the yellowing inhibition effect, it is preferable that the content of the adhesive layer or the inorganic layer be low, and it is preferable that the adhesive layer or the inorganic layer be substantially not included.

[0214] The multilayer container of the present invention has a multilayer structure of two or more layers, preferably has a structure of 2 to 5 layers, more preferably has a structure of 3 to 5 layers, even more preferably has a structure of 3 layers or 5 layers, and even more preferably has a structure of 3 layers.

[0215] It is preferable that the outermost layer of the multilayer container of the present invention is a polyester layer. In addition, it is preferable that the innermost layer is also a polyester layer, and it is more preferable that both the outermost layer and the innermost layer are polyester layers.

[0216] If the outermost layer is a polyester layer, the multilayer container has excellent impact resistance, appearance, and design properties.

[0217] Here, “outermost layer” refers to a layer existing on the outer surface of the multilayer container, which comes into contact with baling materials or crushers during transport, and is a layer related to the exterior of the container. Additionally, “innermost layer” refers to a layer existing on the inner surface of the multilayer container, which comes into contact with contents, preferably liquid.

[0218] Accordingly, regarding the structure of the multilayer container, it is preferable that the multilayer container has a 2 to 5-layer structure and the outermost layer is a polyester layer, and it is more preferable that the multilayer container has a 3 to 5-layer structure and the outermost and innermost layers are polyester layers.

[0219] In the case of a 2-layer structure, it is preferable that the innermost layer is a polyamide layer / polyester layer, in the case of a 3-layer structure, it is preferable that the innermost layer is a polyester layer / polyamide layer / polyester layer, and in the case of a 5-layer structure, it is preferable that the innermost layer is a polyester layer / polyamide layer / polyester layer / polyamide layer / polyester layer.

[0220] The multilayer container of the present invention is preferably a hollow container, and when the multilayer container is a hollow container, the body has at least a multilayer structure. Furthermore, the ratio of the thickness (W) of the polyester layer in the body to the thickness (S) of the polyamide layer (thickness ratio W / S) is preferably 2.5 or more and 200 or less. Meanwhile, the thickness of the polyester layer refers to the average thickness, and in the case where the polyester layer in the body is a plurality of layers, the thickness of the plurality of layers is averaged to obtain the average thickness per layer. The thickness of the polyamide layer is also the same.

[0221] If the thickness ratio W / S is 2.5 or higher, it is desirable because it is easy to separate the polyamide resin from the polyester resin during the separation process in the method for manufacturing recycled polyester, particularly in balloon separation or specific gravity separation. In addition, if the thickness ratio W / S is 200 or lower, the gas barrier properties of the hollow container are excellent, and the contents can be preserved for a long time.

[0222] In order to improve the separation efficiency in the separation process and to ensure good gas barrier properties of the hollow container, the thickness ratio (W / S) is more preferably 3 to 50 and more preferably 4 to 15.

[0223] In addition, when the multilayer container is a hollow container, the total thickness (i.e., the total thickness of all layers in the hollow container) in the central part of the hollow container is preferably 100 μm to 5 mm, more preferably 150 μm to 3 mm, and even more preferably 200 μm to 2 mm. In addition, 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 to this range, gas barrier properties are secured, and the polyamide layer becomes easier to separate from the polyester during the separation process.

[0224] In the case where the multilayer container is a hollow container, the polyamide layer is preferably present for 50% or more of the outer surface area of ​​the container, more preferably for 70% or more of the outer surface area of ​​the container, even more preferably for 90% or more of the outer surface area of ​​the container, even more preferably for 99% or more of the outer surface area of ​​the container, substantially more preferably for 100% of the outer surface area of ​​the container, and even more preferably for 100% of the outer surface area of ​​the container.

[0225] When the multilayer container of the present invention is a hollow container, it is more preferable that it be a packaging container for liquids used by filling the interior of the hollow container with liquid, and even more preferable that it be a packaging container for beverages. Examples of liquids filled inside include beverages, liquid seasonings, chemicals, pharmaceuticals, detergents, etc., and a beverage is preferred in which deterioration by oxygen can be effectively prevented by the multilayer container of the present invention.

[0226] Beverages include water, carbonated water, oxygenated water, hydrogen water, milk, dairy products, juice, coffee, coffee drinks, carbonated soft drinks, tea, alcoholic beverages, etc.

[0227] Examples of liquid seasonings include sauces, soy sauce, syrups, mirin, and dressings.

[0228] Examples of chemicals include pesticides and insecticides.

[0229] The oxygen barrier properties of the multilayer container of the present invention can be evaluated by an oxygen permeability test according to the MOCON method in accordance with ASTM D3985. The oxygen permeability (cc / (bottle·0.21 atm·day)) of the multilayer container of the present invention is preferably 0.020 or less, more preferably 0.010 or less, and even more preferably 0.005 or less when a total of 25g of resin, in which the mass ratio of the polyester layer to the polyamide layer is 97:3, is made into a 3-layer hollow container with a capacity of 500mL. Meanwhile, the manufacture of the 3-layer hollow container may follow the method of the example.

[0230] For measurement, MOCON's OX-TRAN2 / 61 is used, 100 mL of water is filled into the above 500 mL container, and nitrogen at 1 atm is circulated inside the container at 20 mL / min under conditions of oxygen partial pressure of 0.21 atm, temperature of 23℃, internal humidity of 100% RH, and external humidity of 50% RH, and the oxygen contained in the nitrogen after circulation inside the container is measured by detecting it with a chlorometric sensor.

[0231] [Method for manufacturing a multilayer container]

[0232] There are no limitations on the method of manufacturing the multilayer container of the present invention, but it is preferable to manufacture it by the following method.

[0233] The method for manufacturing a multilayer container according to the present invention preferably comprises a polyester layer containing a polyester resin (X) and a polyamide layer containing a polyamide resin (Y), a yellowing inhibitor (A), and an oxidation promoter (B), wherein the content of the polyamide resin (Y) is 0.05 to 7.0 mass% relative to the total amount of the polyamide layer and the total polyester layer, the yellowing inhibitor (A) is a dye, and the content of the yellowing inhibitor (A) is 1 to 30 ppm relative to the total amount of the polyamide layer and the total polyester layer. The method comprises: a process 1 of preparing a polyamide resin mixture by mixing the polyamide resin (Y), the yellowing inhibitor (A), and the oxidation promoter (B); a process 2 of obtaining a multilayer preform by injection molding the polyamide resin mixture and the polyester resin composition containing the polyester resin (X); and a process 3 of blow-molding the multilayer preform.

[0234] <Process 1 (Process for preparing a polyamide resin mixture)>

[0235] In Process 1, a polyamide resin (Y), a yellowing inhibitor (A), and an oxidation accelerator (B) are mixed to prepare a polyamide resin mixture.

[0236] Typically, in order to spread a yellowing inhibitor throughout a container, equipment for stirring and mixing or kneading the yellowing inhibitor and all resins is required. However, in the method for manufacturing a multilayer container according to the present invention, by mixing a yellowing inhibitor (A) and an oxidation accelerator (B) with a small amount of polyamide resin (Y), the yellowing inhibitor can be efficiently spread throughout the container with a small scale and short mixing time, resulting in excellent productivity.

[0237] The mixing method may be a dry blend or a melt blend; however, from the perspective of minimizing thermal history to prevent degradation of the resin or yellowing inhibitor, a dry blend or a masterbatch melt blend is preferred. Additionally, from the perspective of preventing the yellowing inhibitor from adhering to and remaining on the molding machine or around the molding machine in Process 2, a melt blend is preferred, and among these, the masterbatch method is preferred from the perspective of minimizing thermal history to prevent degradation of the resin or yellowing inhibitor.

[0238] In Process 1, it is preferable to mix the pellet-shaped polyamide resin (Y), yellowing inhibitor (A), and oxidation accelerator (B) at 230°C or lower, more preferable to mix at 150°C or lower, and even more preferable to mix at 100°C or lower. By mixing at 230°C or lower, the thermal history is reduced, thereby preventing the deterioration of the resin or the yellowing inhibitor. This is because the polyamide resin can maintain its pellet-shaped form, which is thought to result in less thermal degradation. When mixing at 230°C or lower, it is preferable to perform a dry blend.

[0239] The yellowing inhibitor (A) appropriately used in Process 1 is the same as that described in the above (yellowing inhibitor (A)), is a dye, and is more preferably an anthraquinone-based dye.

[0240] In addition, the yellowing inhibitor (A) is preferably in the form of a powder, a dispersion, or a solution, and is more preferably in the form of a powder. Since the yellowing inhibitor (A) is in these forms, it can be mixed more easily and uniformly with the polyamide resin (Y).

[0241] The oxidation promoter (B) appropriately used in Process 1 is the same as that described in the above (oxidation promoter (B)). Specifically, it is preferable that it be a compound containing a transition metal, and at least one selected from the group consisting of carboxylates, carbonates, acetylacetonate complexes, oxides, and halides containing a transition metal is preferred, at least one selected from octanoates, neodecanoates, naphthenates, stearates, acetates, carbonates, and acetylacetonate complexes is more preferred, and cobalt carboxylates such as cobalt octanoate, cobalt naphthenate, cobalt acetate, cobalt neodecanoate, and cobalt stearate are even more preferred.

[0242] In addition, in process 1, it is preferable to additionally mix in a greening inhibitor (C).

[0243] The greening inhibitor (C) appropriately used in Process 1 is the same as described in the above (greening inhibitor (C)), and is preferably at least one selected from the group consisting of dyes and pigments, more preferably at least one selected from the group consisting of anthraquinone dyes and azo dyes, even more preferably at least one selected from the group consisting of anthraquinone red dyes and azo red dyes, and from the perspective of heat resistance, it is even more preferable that it be anthraquinone red dye.

[0244] In addition, the greening inhibitor (C) is preferably in the form of a powder, a dispersion, or a solution, and is more preferably in the form of a powder. Since the greening inhibitor (C) is in these forms, it can be mixed more easily and uniformly with the polyamide resin (Y).

[0245] Furthermore, in process 1, it is preferable to mix polyester resin (Z).

[0246] The polyester resin (Z) appropriately used in Process 1 is the same as that described in the above (polyester resin (Z)). When mixing by dry blending, it is preferable to mix the polyester resin (Z) in the form of pellets.

[0247] Mixing devices used for dry blending include tumbler mixers, ribbon mixers, Henschel mixers, Banbury mixers, etc.

[0248] In Process 1, the method of mixing the polyamide resin (Y), yellowing inhibitor (A), and oxidation accelerator (B) into a melt blend may include the masterbatch method and the full compound method, and the masterbatch method is preferred.

[0249] The masterbatch method is a method in which, in Process 1, a polyamide resin or polyester resin is kneaded with a yellowing inhibitor (A) and an oxidation accelerator (B), and then mixed with a polyamide resin (Y).

[0250] The masterbatch method is a method in which, in Process 1, a small amount of polyamide resin or polyester resin is kneaded with a yellowing inhibitor (A) and an oxidation accelerator (B) to form a masterbatch, and then mixed with the remaining amount of polyamide resin (Y). Additionally, when obtaining the masterbatch, a greening inhibitor (C) may also be kneaded simultaneously. That is, in Process 1, it is preferable to knead the polyamide resin or polyester resin with the yellowing inhibitor (A) and the oxidation accelerator (B) and then mix with the polyamide resin (Y), and it is more preferable to knead the polyamide resin or polyester resin, the yellowing inhibitor (A), the oxidation accelerator (B), and the greening inhibitor (C) in Process 1 and then mix with the polyamide resin (Y).

[0251] For the masterbatch, it is preferable to use a polyamide resin or a polyester resin; using a polyamide resin is preferable in terms of miscibility with the polyamide resin (Y), and using a polyester resin is preferable in terms of suppressing yellowing caused by thermal history. Meanwhile, a mixture of these may also be used.

[0252] In particular, it is more preferable that the yellowing inhibitor (A) be a masterbatch mixed with a polyamide resin (a masterbatch containing a polyamide resin and a yellowing inhibitor (A), and a polyamide resin composition), and it is more preferable that the oxidation accelerator (B) be a masterbatch mixed with a polyester resin (a masterbatch containing a polyester resin and an oxidation accelerator (B), and a polyester resin composition). In addition, it is preferable that the greening inhibitor (C) be a masterbatch mixed with a polyamide resin (a masterbatch containing a polyamide resin, a yellowing inhibitor (A), and a greening inhibitor (C), and a polyamide resin composition).

[0253] The polyamide resin used in the masterbatch is preferably polyamide resin (Y), and more preferably is the same as the remainder of the polyamide resin (Y).

[0254] The polyester resin used in the masterbatch is preferably polyester resin (Z). Additionally, the same as polyester resin (X) may be used, or the same as polyester resin (X) of the polyester layer may be used.

[0255] The amount of polyamide resin or polyester resin used in the masterbatch is preferably 1 to 20 mass% with respect to the total resin amount of the polyamide layer, and more preferably 3 to 15 mass%.

[0256] As a method for obtaining a masterbatch, when a polyamide resin or polyester resin is mixed with a yellowing inhibitor (A) and an oxidation accelerator (B), if the melting point of the resin used in the masterbatch is Tm, the mixing temperature (°C) is preferably Tm+5 to Tm+60, more preferably Tm+10 to Tm+50, and even more preferably Tm+15 to Tm+40 from the perspective of sufficient mixing. Specifically, 245 to 300°C is more preferably 250 to 290°C is more preferably 255 to 280°C is even more preferably 255 to 280°C is even more preferably 10 to 600 seconds, more preferably 20 to 400 seconds, and even more preferably 30 to 300 seconds from the perspective of sufficient mixing. Devices used for mixing include open-type mixing rolls, closed-type Banbury mixers, kneaders, and continuous mixers (single-axis mixers, twin-axis mixers, multi-axis mixers, etc.).

[0257] In addition, methods for mixing the masterbatch and the remaining polyamide resin (Y) include dry blending and further kneading, but dry blending is preferred from the perspective of minimizing thermal history. For dry blending, it is preferable to mix the pellets of the masterbatch and the pellets of the remaining polyamide resin (Y) using a mixing device such as a tumble mixer.

[0258] When the polyamide layer of the multilayer container obtained contains a polyester resin (Z), the method of mixing the masterbatch, the remainder of the polyamide resin (Y), and the remainder of the polyester resin (Z) may include a dry blend and further a kneading method, and a dry blend is preferred. For the dry blend, it is preferable to mix the pellets of the masterbatch, the pellets of the remainder of the polyamide resin (Y), and the pellets of the remainder of the polyester resin (Z) using a mixing device such as a tumble mixer.

[0259] The full compound method is a method of mixing all of the polyamide resin (Y) used in the polyamide layer with a yellowing inhibitor (A) and an oxidation accelerator (B) by kneading.

[0260] Meanwhile, when the polyamide layer of the obtained multilayer container contains a polyester resin (Z), the entire amount of polyamide resin (Y) used in the polyamide layer, the entire amount of polyester resin (Z), a yellowing inhibitor (A), and an oxidation accelerator (B) are kneaded and mixed.

[0261] From the perspective of sufficient mixing, the mixing temperature is preferably 245 to 300°C, more preferably 250 to 290°C, and even more preferably 255 to 280°C. In addition, from the perspective of sufficient mixing, the mixing 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 mixing include open-type mixing rolls, closed-type Banbury mixers, kneaders, and continuous mixers (single-axis mixers, twin-axis mixers, multi-axis mixers, etc.).

[0262] It is preferable that the composition of the polyamide resin mixture obtained in this process be the same as the composition of the <polyamide layer> above.

[0263] <Process 2 (Process for obtaining a multilayer preform)>

[0264] In process 2, a polyester resin composition comprising the above polyamide resin mixture and polyester resin (X) is injection molded to obtain a multilayer preform.

[0265] It is preferable that the above polyester resin composition has the same composition as the above <polyester layer>.

[0266] In co-injection molding, a mixture of polyester resin and polyamide resin is extruded into a mold, respectively, and co-injection molded to form a multilayer preform.

[0267] <Process 3 (Blow molding process)>

[0268] In process 3, the above multilayer preform is blow-molded.

[0269] In the method for manufacturing a multilayer container of the present invention, it is preferable to mold the multilayer preform (multilayer parison) obtained by process 2 by stretching blow.

[0270] Among these, in process 2, it is preferable to perform a multilayer preform obtained by injection molding by stretching blow molding, and it is more preferable to perform a multilayer preform obtained by injection molding by biaxial stretching blow molding. Meanwhile, regarding the conditions for biaxial stretching blow molding, it is preferable to set the preform heating temperature to 95~110℃, the first blow pressure to 0.5~1.2MPa, and the second blow pressure to 2.0~2.6MPa. Accordingly, the occurrence of thickness non-uniformity or stretching non-uniformity is suppressed, and a multilayer container with excellent strength can be obtained.

[0271] [Method for manufacturing recycled polyester]

[0272] The multilayer container of the present invention is suitable for recycling as described above, and recycled polyester can be manufactured using the multilayer container of the present invention as a raw material.

[0273] The method for manufacturing recycled polyester according to the present invention preferably includes a process for recovering polyester from the multilayer container.

[0274] That is, it is preferable to have a process for recovering polyester from a multilayer container having a polyester layer containing a polyester resin (X) and a polyamide layer containing a polyamide resin (Y), a yellowing inhibitor (A), and an oxidation promoter (B), wherein the content of the polyamide resin (Y) is 0.05 to 7.0 mass% relative to the total amount of the polyamide layer and the total polyester layer, the yellowing inhibitor (A) is a dye, and the content of the yellowing inhibitor (A) is 1 to 30 ppm relative to the total amount of the polyamide layer and the total polyester layer.

[0275] A method for manufacturing recycled polyester from a multilayer container preferably involves removing all or part of the polyamide layer from the multilayer container, recovering the polyester constituting the polyester layer, and using the polyester as recycled polyester. Meanwhile, the method for manufacturing recycled polyester from a multilayer container is not limited to the above method, and may be a method for manufacturing recycled polyester without undergoing a process of removing the polyamide resin.

[0276] The recycled polyester obtained by the present manufacturing method can be used for various purposes, such as resin molded articles and fibers.

[0277] Hereinafter, the method for manufacturing the recycled polyester of the present invention is described in detail.

[0278] In the present manufacturing method, the multilayer container is typically used after being used up, but it may also be an unused item. Examples of used multilayer containers include those that have been collected after being distributed in the market.

[0279] In the present manufacturing method, first, if a lid is attached to a multilayer container, it is preferable to separate the lid from the multilayer container.

[0280] Next, the container is crushed, washed as needed, and separated to selectively extract polyester as needed, and recovered as recycled polyester (recovery process).

[0281] Next, if necessary, assembly is performed to form pellets (assembly process).

[0282] Furthermore, if necessary, a crystallization process and a solid-state polymerization process are performed (crystallization / solid-state polymerization process).

[0283] Each process is explained below.

[0284] Recovery Process

[0285] The recovery process is a process of recovering recycled polyester by crushing multilayer containers.

[0286] Among these, it is preferable to selectively extract polyester by removing all or part of the polyamide layer after crushing the multilayer container, and it is more preferable to separate the polyester from the polyamide resin constituting the polyamide layer.

[0287] The crushing of the multilayer container can be performed using a crusher such as a single-screw crusher, a twin-screw crusher, a tri-screw crusher, or a cutter mill. The crushed material obtained by crushing is, for example, in the form of flakes, powder, or lumps. However, since the multilayer container has a multilayer stacked structure with a thickness of several mm or less, such as copper, most of the crushed material is usually in the form of flakes. Meanwhile, a crushed material in the form of flakes refers to a material that is in the form of a thin or flat shape with a thickness of about 2 mm or less.

[0288] In addition, in a multilayer container, the polyester layer and the polyamide layer are structurally integrated, but typically, they are not bonded to each other, and in the crushing process, the polyester and polyamide resins are easily separated as separate crushed materials. Also, by making them into flakes, they become easy to separate by being wound up by the airflow of the balloon separation described later.

[0289] However, polyester and polyamide resin cannot be completely separated during the grinding process, and the ground material is separated into a material with a relatively high polyester content and a material with a relatively low polyester content and a relatively high polyamide resin content. Meanwhile, for the sake of convenience of explanation, 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.

[0290] As described above, the ground material is separated into polyester and polyamide resin (separation process).

[0291] As a separation method, it is preferable to use gravity separation utilizing the difference in specific gravity between polyester and polyamide resins.

[0292] That is, it is preferable to remove the polyamide layer by balloon separation after crushing the multilayer container.

[0293] Specific gravity separation, specifically, can be exemplified by balloon separation, which separates crushed materials using wind power. Balloon separation is a method, for example, in which, within a separation device capable of generating an internal rotating airflow, crushed materials that come into contact with the airflow generated by the separation device are separated and recovered into those that fall naturally by their own weight due to high specific gravity or a small specific surface area, and those that are wound up by the airflow due to low specific gravity or a large specific surface area.

[0294] In this method, the crushed polyester material falls naturally due to its own weight, while the crushed polyamide resin material is lifted up, so that it becomes possible to separate and recover the polyester and polyamide resin.

[0295] In such balloon separation, the same operation may be repeated on the same crushed material. For example, the naturally fallen material may be further balloon separated to increase the polyester content in the recycled polyester.

[0296] Meanwhile, separation methods are not limited to balloon separation, and include methods such as 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, and methods of separating the crushed material by applying a constant vibration to the crushed material to separate it from materials with different specific gravities.

[0297] Assembly Process

[0298] It is preferable to aggregate the recovered recycled polyester into pellets to facilitate handling during molding processes and the like.

[0299] The assembly may be performed either before or after the crystallization / solid-state polymerization process described later, but it is better to perform it before the crystallization / solid-state polymerization process. By performing it before the crystallization / solid-state polymerization process, the handling properties during the crystallization / solid-state polymerization process are also improved.

[0300] In the granulation process, it is preferable to plasticize the crushed material using a melt blend to granulate it. Examples of granulation devices for plasticizing and granulating include single-screw extruders, twin-screw extruders, and multi-screw extruders, but any known device may be used. Regarding the shape of the pellets, it is preferable for them to be cylindrical, spherical, or elliptical.

[0301] For assembly, it is preferable to extrude plasticized recycled polyester into a strand and cut it into pellets with a pelletizer while cooling it in a water bath. The pellets removed from the water bath are typically dried to remove moisture attached to the surface.

[0302] Crystallization / Solid-state Polymerization Process

[0303] After the process of recovering the polyester described above, it is preferable to perform one or more processes selected from a crystallization process and a solid-state polymerization process, and it is more preferable to perform both the crystallization process and the solid-state polymerization process. The crystallization / solid-state polymerization process is preferably performed on the pelletized polyester described above, but it may also be performed on materials that are not pelletized (e.g., crushed materials).

[0304] Meanwhile, when performing both crystallization and solid-state polymerization, it is preferable to crystallize the polyester first and then perform solid-state polymerization.

[0305] Crystallization of the polyester is carried out by maintaining the polyester under a constant heat. It is preferable to carry out crystallization by heating the polyester at, for example, 100 to 230°C. By crystallizing the polyester, it is prevented that the polyesters fuse together or adhere to the inner surface of the device during solid-state polymerization or molding processing.

[0306] It is preferable that solid-state polymerization be carried out by maintaining the temperature for a certain period of time at a temperature above (melting point of polyester - 80°C) and below the melting point of polyester. By keeping the temperature below the melting point, the polyester is prevented from melting, and, for example, the polyester is prevented from adhering to the surface of the equipment, thereby preventing a decrease in work efficiency. In addition, by keeping the temperature above (melting point - 80°C), polymerization proceeds at a sufficient polymerization rate, making it easier to obtain desired physical properties.

[0307] Solid-state polymerization may be carried out under vacuum or under an inert gas stream such as nitrogen or argon. When carried out under vacuum, a value of 1.0 torr or less is preferred, 0.5 torr or less is more preferred, and 0.1 torr or less is even more preferred. In addition, whether under vacuum or under an inert gas stream such as nitrogen or argon, it is desirable to minimize the oxygen concentration remaining in the system, 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, it becomes difficult to cause appearance defects such as yellowing.

[0308] When solid-state polymerization is carried out under vacuum, it is desirable to maintain uniform heat transfer while constantly repeating the stirring or mixing of the polyester. When carried out in the presence of an inert gas, it is desirable to maintain the surface of the polyester in contact with the dry gas at all times under a dry gas stream.

[0309] Examples of solid-state polymerization apparatuses for performing crystallization / solid-state polymerization processes include a tumbler-type batch apparatus equipped with a heating jacket, a drying silo type equipped with an inert gas flow system, a crystallization apparatus equipped with internal stirring blades and a discharge screw, and a reactor. Meanwhile, it is preferable that crystallization and solid-state polymerization be performed continuously or simultaneously in the same apparatus.

[0310] The heating time for solid-state polymerization is determined in a timely manner based on the apparatus and other conditions, provided that it is sufficient for the polyester to obtain sufficient physical properties.

[0311] Since solid-state polymerization involves maintaining the polyester for an extended period at high temperatures, the presence of impurities in the polyester can degrade quality, such as color tone. It is desirable that most of the polyamide resin be removed during the aforementioned removal process; in this case, the potential for quality deterioration during solid-state polymerization is minimized.

[0312] In the method for manufacturing recycled polyester of the present invention, processes other than those described above may be carried out, and a cleaning process may be performed to remove contents attached to the inside of a multilayer container. Cleaning is preferably performed by rinsing with a liquid, and cleaning with water, cleaning with an alkaline aqueous solution, or both may be performed.

[0313] In addition, washing may be performed before the multilayer container is crushed or after crushing, but it is preferable to perform it before any one of aggregation, crystallization, or solid-state polymerization. Furthermore, the washing process may be performed simultaneously with the crushing process using a crusher that performs washing and crushing simultaneously, called a wet crusher.

[0314] In addition, if a washing process is performed, a drying process may be performed after the washing process. By performing a drying process, the moisture content of the recycled polyester obtained by this method can be reduced, thereby increasing thermal stability and making it possible to provide high-quality recycled polyester. The drying process can be performed, for example, using air blowing by a dryer or hot air.

[0315] When the method for manufacturing recycled polyester includes a process for removing polyamide resin, the polyamide resin content 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.

[0316] Examples

[0317] The present invention will be explained more specifically below using examples and comparative examples, but the present invention is not limited to these examples.

[0318] [raw material]

[0319] The polyester resin, yellowing inhibitor, oxidation accelerator, and greening inhibitor used in the examples and comparative examples are as follows. In addition, the polyamide resin used was the one prepared in Preparation Example 1 below.

[0320] Polyester resin (X1)

[0321] Isophthalic acid copolymer polyethylene terephthalate (intrinsic viscosity: 0.83 dL / g, melting point: 248°C), isophthalic acid modification rate 1.5 mol% (in dicarboxylic acid units), trade name: BK2180, manufactured by Mitsubishi Chemical Corporation

[0322] Yellowing Inhibitor

[0323] Blue RR: Solvent Blue 97 (anthraquinone dye), Trade Name: MACROLEX Blue RR Gran, Manufactured by LANXESS

[0324] K6907: Pigment Blue 15:1 (Type α Copper Phthalocyanine Pigment), Product Name: HELIOGEN BLUE K6907, Manufactured by BASF, Form: Powder

[0325] Oxidation promoter

[0326] Cobalt stearate(II): Tokyo Kasei Kogyo Co., Ltd.

[0327] Cobalt (II) neodecanoate: Japan Chemical Industry Co., Ltd.

[0328] Green Stool Inhibitor

[0329] Violet 3R: Solvent Violet 36 (anthraquinone dye), Trade name: MACROLEX Violet 3R Gran, manufactured by LANXESS

[0330] K4535: Pigment Red 202 (Quinacridone-based pigment), Trade name: Cinquasia Magenta K4535, Manufactured by BASF

[0331] Polyester resin (Z1)

[0332] Isophthalic acid copolymer polyethylene terephthalate (intrinsic viscosity: 0.83 dL / g, melting point: 248°C), trade name: BK2180, manufactured by Mitsubishi Chemical Corporation

[0333] <Polyamide resin (Y1)>

[0334] Preparation Example 1 (Preparation of polyamide resin (Y1))

[0335] In a reaction vessel with a capacity of 50 liters equipped with a stirrer, a condenser, a condenser, a thermometer, a dropping funnel, a nitrogen inlet tube, and a strand die, 15,000 g (102.6 mol) of weighed adipic acid, 13.06 g (123.3 mmol, 151 ppm as the phosphorus concentration in the polyamide), and 6.849 g (83.49 mmol, 0.68 as the molar ratio to sodium hypophosphite monohydrate) were added, and the mixture was sufficiently nitrogen-substituted. Afterward, the mixture was heated to 170°C while stirring the system under an additional small stream of nitrogen. To this, 13,896 g (102.0 mol, 0.994 as an input molar ratio) of metaxylylenediamine was added dropwise under stirring, and the temperature inside the system was continuously increased while removing the generated condensation water from the system. After the dropwise addition of metaxylylenediamine was finished, the internal temperature was raised to 260°C and the reaction was continued for 40 minutes. Subsequently, the system was pressurized with nitrogen, the polymer was removed from the strand die, and the polymer was pelletized to obtain approximately 24 kg of polyamide.

[0336] Next, the polyamide was introduced into a jacketed tumble dryer equipped with a nitrogen gas inlet pipe, a vacuum line, a vacuum pump, and a thermocouple for measuring internal temperature. While rotating the tumble dryer at a constant speed, the interior of the tumble dryer was sufficiently replaced with nitrogen gas having a purity of 99 volume% or higher. Subsequently, the tumble dryer was heated under a stream of nitrogen gas, 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. Then, the heating was continued, and the pellet temperature was raised to 200°C over approximately 70 minutes, after which it was maintained at 200°C for 30 to 45 minutes. Subsequently, nitrogen gas having a purity of 99 volume% or higher was introduced into the system, and the polyamide resin (Y1) was obtained by cooling while the tumble dryer was rotating.

[0337] [evaluation]

[0338] The multilayer container of the present invention was evaluated by the following method.

[0339] Oxygen Permeability (Evaluation of Oxygen Barrier Properties)

[0340] Oxygen permeability was evaluated by the following method.

[0341] Oxygen permeability testing was performed according to the MOCON method in accordance with ASTM D3985. MOCON's OX-TRAN2 / 61 was used for the measurement. 100 mL of water was filled into a 500 mL bottle obtained in each example and comparative example, and nitrogen at 1 atm was circulated inside the bottle at a rate of 20 mL / min under conditions of an oxygen partial pressure of 0.21 atm, a temperature of 23°C, an internal bottle humidity of 100% RH, and an external humidity of 50% RH. The measurement was performed by detecting the oxygen contained in the nitrogen after circulation inside the bottle using a chromatographic sensor. The lower measurement limit was set to 0.001 cc / (bottle·day·0.21 atm).

[0342] It was determined by the oxygen permeability value after 7 days from the start of measurement. The smaller the oxygen permeability value, the better the oxygen barrier performance.

[0343] <Yellowness Δb * (Evaluation of yellowing inhibition ability)

[0344] Yellowness Δb of the recycled polyester pellet obtained in [Manufacture of Recycled Polyester] described below * It was measured by the following methods and evaluated according to the following criteria.

[0345] The color tone of the pellet was measured based on JIS Z 8722 using a colorimeter ZE-2000 (manufactured by Japan Color Industry, 12V 20W halogen lamp light source), by filling a 30mmΦ cell container with pellets and measuring four times using the reflection method as the average value.

[0346] Meanwhile, b * The value represents chromaticity. +b * is the yellow direction, -b * indicates the blue direction. Also, Δb * A smaller absolute value indicates that yellowing is suppressed. It also signifies a higher degree of colorlessness. Δb *The value is b of the sample in the following examples and comparative examples. * The value and b of the polyester resin body subjected to the same treatment as the examples and comparative examples. * Indicates the difference from the value.

[0347] <Greenness Δa * >

[0348] Greenness Δa of the recycled polyester pellet obtained in [Manufacture of Recycled Polyester] described below * It was measured by the following methods and evaluated according to the following criteria.

[0349] The color tone of the pellet was measured based on JIS Z 8722 using a colorimeter ZE-2000 (manufactured by Japan Color Industry, 12V 20W halogen lamp light source), by filling a 30mmΦ cell container with pellets and measuring four times using the reflection method, and the average value was determined.

[0350] Meanwhile, a * The value represents color intensity. +a * is the positive direction, -a * indicates the green direction. Also, Δa * A smaller absolute value indicates that greening is suppressed. It also signifies a higher degree of colorlessness. Δa * The value is a of the sample of the following examples and comparative examples. * Value and a of a polyester resin body subjected to the same treatment as the examples and comparative examples * Indicates the difference from the value.

[0351] [Preparation of Polyamide Resin Mixtures by Masterbatch Method]

[0352] Preparation Example 2

[0353] 95.35 mass% of polyamide resin (Y1), 0.20 mass% of BlueRR as a yellowing inhibitor, 4.25 mass% of cobalt stearate (II) as an oxidation accelerator, and 0.20 mass% of Violet3R as a greening inhibitor were pre-dry-blended. Next, this dry-blended mixture was melt-kneaded at 260°C using a twin-screw extruder (Toshiba Machinery, TEM26SX) to obtain masterbatch pellets. Subsequently, the pellets were dried in a vacuum dryer at 150°C for 5 hours to obtain masterbatch A.

[0354] Next, the obtained masterbatch A and the remainder of the polyamide resin (Y1) were mixed in the mass ratio of Table 1 (masterbatch A / remainder of polyamide resin = 10 / 90) to prepare a polyamide resin mixture.

[0355] Preparation Example 3

[0356] 94.95 mass% of polyamide resin (Y1), 0.40 mass% of BlueRR as a yellowing inhibitor, 4.25 mass% of cobalt stearate (II) as an oxidation accelerator, and 0.40 mass% of Violet3R as a greening inhibitor were pre-dry-blended. Next, this dry-blended mixture was melt-kneaded at 260°C using a twin-screw extruder (Toshiba Machinery, TEM26SX) to obtain masterbatch pellets. Subsequently, the pellets were dried in a vacuum dryer at 150°C for 5 hours to obtain masterbatch B.

[0357] Next, the obtained masterbatch B and the remainder of the polyamide resin (Y1) were mixed in the mass ratio of Table 1 (masterbatch B / remainder of polyamide resin = 10 / 90) to prepare a polyamide resin mixture.

[0358] Preparation Example 4

[0359] 96.48 mass% of polyamide resin (Y1), 0.40 mass% of BlueRR as a yellowing inhibitor, 2.72 mass% of cobalt (II) neodecanoate as an oxidation accelerator, and 0.40 mass% of Violet3R as a greening inhibitor were pre-dry-blended. Next, this dry-blended mixture was melt-kneaded at 260°C using a twin-screw extruder (Toshiba Machinery, TEM26SX) to obtain masterbatch pellets. Subsequently, the pellets were dried in a vacuum dryer at 150°C for 5 hours to obtain masterbatch C.

[0360] Next, the obtained masterbatch C and the remainder of the polyamide resin (Y1) were mixed in the mass ratio of Table 1 (masterbatch C / remainder of the polyamide resin = 10 / 90) to prepare a polyamide resin mixture.

[0361] Preparation Example 5

[0362] 97.08 mass% of polyamide resin (Y1), 0.40 mass% of BlueRR as a yellowing inhibitor, 2.12 mass% of cobalt stearate (II) as an oxidation accelerator, and 0.40 mass% of Violet3R as a greening inhibitor were pre-dry-blended. Subsequently, this dry-blended mixture was melt-kneaded at 260°C using a twin-screw extruder (Toshiba Machinery, TEM26SX) to obtain masterbatch pellets. Afterward, the pellets were dried in a vacuum dryer at 150°C for 5 hours to obtain masterbatch D.

[0363] Next, the obtained masterbatch D and the remainder of the polyamide resin (Y1) were mixed in the mass ratio of Table 1 (masterbatch D / remainder of polyamide resin = 10 / 90) to prepare a polyamide resin mixture.

[0364] Preparation Example 6

[0365] 95.35 mass% of polyamide resin (Y1), 0.40 mass% of BlueRR as a yellowing inhibitor, and 4.25 mass% of cobalt stearate (II) as an oxidation accelerator were pre-dry-blended. In this dry-blended mixture, no greening inhibitor was added. Next, this dry-blended mixture was melt-kneaded at 260°C using a twin-screw extruder (Toshiba Machinery, TEM26SX) to obtain masterbatch pellets. Subsequently, the pellets were dried in a vacuum dryer at 150°C for 5 hours to obtain masterbatch E.

[0366] Next, the obtained masterbatch E and the remainder of the polyamide resin (Y1) were mixed in the mass ratio of Table 1 (masterbatch E / remainder of polyamide resin = 10 / 90) to prepare a polyamide resin mixture.

[0367] Preparation Example 7

[0368] 94.95 mass% of polyester resin (X1), 0.40 mass% of BlueRR as a yellowing inhibitor, 4.25 mass% of cobalt stearate (II) as an oxidation accelerator, and 0.40 mass% of Violet3R as a greening inhibitor were pre-dry-blended. Subsequently, this dry-blended mixture was melt-kneaded at 260°C using a twin-screw extruder (Toshiba Machinery, TEM26SX) to obtain masterbatch pellets. Afterward, the pellets were dried in a vacuum dryer at 150°C for 5 hours to obtain masterbatch F.

[0369] Next, the obtained masterbatch F and the remainder of the polyamide resin (Y1) were mixed in the mass ratio of Table 1 (masterbatch F / remainder of polyamide resin = 10 / 90) to prepare a polyamide resin mixture.

[0370] Preparation Example 8

[0371] 93.75 mass% of polyamide resin (Y1), 0.40 mass% of pigment K6907 as a yellowing inhibitor, 4.25 mass% of cobalt stearate (II) as an oxidation accelerator, and 1.60 mass% of pigment K4535 as a greening inhibitor were pre-dry-blended. Subsequently, this dry-blended mixture was melt-kneaded at 260°C using a twin-screw extruder (Toshiba Machinery, TEM26SX) to obtain masterbatch pellets. Afterward, the pellets were dried in a vacuum dryer at 150°C for 5 hours to obtain masterbatch G.

[0372] Next, the obtained masterbatch G and the remainder of the polyamide resin (Y1) were mixed in the mass ratio of Table 1 (masterbatch G / remainder of polyamide resin = 10 / 90) to prepare a polyamide resin mixture.

[0373] Preparation Example 9

[0374] 95.75 mass% of polyamide resin (Y1) and 4.25 mass% of cobalt stearate (II) as an oxidation accelerator were pre-dry-blended. Subsequently, this dry-blended mixture was melt-kneaded at 260°C using a twin-screw extruder (Toshiba Machinery, TEM26SX) to obtain masterbatch pellets. Afterward, the pellets were dried in a vacuum dryer at 150°C for 5 hours to obtain masterbatch H.

[0375] Next, the obtained masterbatch H and the remainder of the polyamide resin (Y1) were mixed in the mass ratio of Table 1 (masterbatch H / remainder of polyamide resin = 10 / 90) to prepare a polyamide resin mixture.

[0376] [Preparation of a polyamide resin mixture containing polyester resin]

[0377] Preparation Example 10 (Polyamide resin composition (Y2))

[0378] 99.2 mass% of polyamide resin (Y1), 0.4 mass% of BlueRR as a yellowing inhibitor, and 0.4 mass% of Violet3R as a greening inhibitor were pre-dry-blended. Subsequently, this dry-blended mixture was melt-kneaded at 260°C using a twin-screw extruder (Toshiba Machinery, TEM26SX) to obtain masterbatch pellets. Afterward, the pellets were dried in a vacuum dryer at 150°C for 5 hours to obtain a polyamide resin composition (Y2).

[0379] Preparation Example 11 (Polyester resin composition (Z2))

[0380] 95.75 mass% of polyester resin (Z1) and 4.25 mass% of cobalt stearate (II) as an oxidation accelerator were pre-dry-blended. Subsequently, this dry-blended mixture was melt-kneaded at 280°C using a twin-screw extruder (Toshiba Machinery, TEM26SX) to obtain masterbatch pellets. Afterward, the pellets were dried in a vacuum dryer at 150°C for 5 hours to obtain a polyester resin composition (Z2).

[0381] Preparation Examples 12-18 (Polyamide resin mixture containing polyester resin)

[0382] A polyamide resin (Y1), a polyamide resin composition (Y2), a polyester resin (Z1), and a polyester resin composition (Z2) were mixed in the mass ratios shown in Table 2 to prepare a polyamide resin mixture. In Table 2, each polyamide resin mixture is indicated by a preparation example number.

[0383] [Manufacture of multilayer containers]

[0384] Examples 1–13 and Comparative Examples 1–4

[0385] Preform Molding

[0386] An injection molding machine having two injection cylinders (manufactured by Sumitomo Heavy Industries, Inc., model DU130CI) and a two-stage mold (manufactured by Kortec) were used. Polyester resin (X1) was injected from one injection cylinder, and the polyamide resin mixture obtained in Preparation Examples 2 to 18 was injected from the other injection cylinder. Under the conditions shown below, a three-layer preform consisting of a polyester layer / polyamide layer / polyester layer (set to be equivalent to 25g per preform) was manufactured by injection molding such that the mass of the polyamide layer relative to the entire preform was the amount listed in Tables 1 and 2. The shape of the preform was an overall length of 95mm, an outer diameter of 22mm, and a thickness of 4.0mm. The molding conditions for the three-layer preform are as shown below.

[0387] Skin-side injection cylinder temperature: 285℃

[0388] Core-side injection cylinder temperature (3rd layer only): 265℃

[0389] Resin flow path temperature inside mold: 285℃

[0390] Mold cooling water temperature: 15℃

[0391] Cycle time: 40 seconds

[0392] Bottle molding

[0393] The preform obtained above was biaxially stretched blow-molded using a blow-molding device (EFB1000ET, manufactured by Frontier) to obtain a bottle (hollow multilayer container). The total length of the bottle is 223 mm, the outer diameter is 65 mm, and the internal volume is 500 mL; the bottom part is petaloid in shape. No dimples were provided in the body. The biaxially stretched blow-molding conditions are as shown below.

[0394] Oxygen permeability was evaluated using the bottles obtained in Examples 1 to 7 and Comparative Examples 1 to 2. The results are shown in Table 1.

[0395] Preform heating temperature: 103℃

[0396] Pressure for stretching rod: 0.7MPa

[0397] Primary blow pressure: 1.1 MPa

[0398] Secondary blow pressure: 2.5 MPa

[0399] 1st blow delay: 0.30 seconds

[0400] 1st blow time: 0.30 seconds

[0401] Secondary blow time: 2.0 seconds

[0402] Blow-off time: 0.6 seconds

[0403] Mold temperature: 30℃

[0404] [Manufacture of Recycled Polyester]

[0405] Recovery and Assembly Process

[0406] 10 kg of hollow multilayer containers obtained in Examples 1 to 13 and Comparative Examples 1 to 4 were crushed using a crusher with a mesh diameter of 8 mm, and the resulting flake-shaped crushed material was recovered as recycled polyester.

[0407] The recovered recycled polyester was extruded using a twin-screw extruder (Toshiba Machinery, TEM26SX) at a heater temperature of 270°C and a discharge speed of 20 kg / hour to form a strand, and then cut with a pelletizer while cooling in a water bath to form pellets. Meanwhile, in Examples 1 to 13 and Comparative Examples 1 to 4, balloon separation of the polyamide layer was not performed.

[0408] Crystallization / Solid-state Polymerization Process

[0409] The pellets obtained from the above assembly process were heated at 200°C for 7 hours under a vacuum with a reduced pressure of 1 torr or less. The pellets were removed after heat treatment, and the yellowness Δb * and greenness Δa * It was evaluated. The results are shown in Table 1 and Table 2.

[0410] [Table 1]

[0411]

[0412] As shown in Table 1, the multilayer container of the example has excellent oxygen barrier properties and can suppress yellowing of the recycled polyester during recycling even with the use of a small amount of yellowing inhibitor.

[0413] [Table 2]

[0414]

[0415] As shown in Table 2, the multilayer container of the example can suppress yellowing of the recycled polyester during recycling even when the polyamide layer contains polyester resin by using a small amount of yellowing inhibitor.

[0416] [Preparation of Polyamide Resin Mixtures or Polyester Resin Mixtures]

[0417] Preparation Example 19 (Preparation of Polyamide Resin Mixture)

[0418] 94.95 mass% of polyamide resin (Y1), 0.40 mass% of BlueRR as a yellowing inhibitor, 4.25 mass% of cobalt stearate (II) as an oxidation accelerator, and 0.40 mass% of Violet3R as a greening inhibitor were pre-dry-blended. Subsequently, this dry-blended mixture was melt-kneaded at 260°C using a twin-screw extruder (Toshiba Machinery, TEM26SX) to obtain masterbatch pellets. Afterward, the pellets were dried in a vacuum dryer at 150°C for 5 hours to obtain masterbatch I.

[0419] Next, the obtained masterbatch I and the remainder of the polyamide resin (Y1) were mixed in the mass ratio of Table 3 (masterbatch I / remainder of the polyamide resin = 10 / 90) to prepare a polyamide resin mixture.

[0420] Preparation Example 20 (Preparation of Polyamide Resin Mixture)

[0421] 95.75 mass% of polyamide resin (Y1) and 4.25 mass% of cobalt stearate (II) as an oxidation accelerator were pre-dry-blended. Subsequently, this dry-blended mixture was melt-kneaded at 260°C using a twin-screw extruder (Toshiba Machinery, TEM26SX) to obtain masterbatch pellets. Afterward, the pellets were dried in a vacuum dryer at 150°C for 5 hours to obtain masterbatch J.

[0422] Next, the obtained masterbatch J and the remainder of the polyamide resin (Y1) were mixed in the mass ratio of Table 3 (masterbatch J / remainder of the polyamide resin = 10 / 90) to prepare a polyamide resin mixture.

[0423] Preparation Example 21 (Preparation of Polyester Resin Mixture)

[0424] 97.60 mass% of polyester resin (X1), 1.20 mass% of BlueRR as a yellowing inhibitor, and 1.20 mass% of Violet3R as a greening inhibitor were pre-dry-blended. Subsequently, this dry-blended mixture was melt-kneaded at 260°C using a twin-screw extruder (Toshiba Machinery, TEM26SX) to obtain masterbatch pellets. Afterward, the pellets were dried in a vacuum dryer at 150°C for 5 hours to obtain masterbatch K.

[0425] Next, the obtained masterbatch K and the remainder of the polyester resin (X1) were mixed in the mass ratio of Table 3 (masterbatch K / remainder of the polyester resin = 5 / 95) to prepare a polyester resin mixture.

[0426] [Manufacture of multilayer containers]

[0427] Example 14 and Comparative Example 5

[0428] Preform Molding

[0429] An injection molding machine having two injection cylinders (manufactured by Sumitomo Heavy Industries, Inc., model DU130CI) and a two-stage molding die (manufactured by Kortec) were used. Polyester resin (X1) (Example 14) or the polyester resin mixture obtained in Preparation Example 21 (Comparative Example 5) was injected from one injection cylinder, and the polyamide resin mixture obtained in Preparation Example 19 (Example 14) or the polyamide resin mixture obtained in Preparation Example 20 (Comparative Example 5) was injected from the other injection cylinder. Under the conditions shown below, a three-layer preform consisting of a polyester layer / polyamide layer / polyester layer (set to be equivalent to 25g per preform) was manufactured by injection molding such that the mass of the polyamide layer relative to the entire preform was the amount listed in Table 3. The shape of the preform was an overall length of 95 mm, an outer diameter of 22 mm, and a thickness of 4.0 mm. The molding conditions for the three-layer preform are as shown below.

[0430] Skin-side injection cylinder temperature: 285℃

[0431] Core-side injection cylinder temperature (3rd layer only): 265℃

[0432] Resin flow path temperature inside mold: 285℃

[0433] Mold cooling water temperature: 15℃

[0434] Cycle time: 40 seconds

[0435] Bottle molding

[0436] The preform obtained above was biaxially stretched blow-molded using a blow-molding device (EFB1000ET, manufactured by Frontier) to obtain a bottle (hollow multilayer container). The total length of the bottle is 223 mm, the outer diameter is 65 mm, and the internal volume is 500 mL; the bottom part is petaloid in shape. No dimples were provided on the part. The biaxially stretched blow-molding conditions are as shown below.

[0437] Preform heating temperature: 103℃

[0438] Pressure for stretching rod: 0.7MPa

[0439] Primary blow pressure: 1.1 MPa

[0440] Secondary blow pressure: 2.5 MPa

[0441] 1st blow delay: 0.30 seconds

[0442] 1st blow time: 0.30 seconds

[0443] Secondary blow time: 2.0 seconds

[0444] Blow-off time: 0.6 seconds

[0445] Mold temperature: 30℃

[0446] [Manufacture of recycled polyester including balloon separation process]

[0447] <Recovery, Balloon Sorting, and Assembly Process>

[0448] 10 kg of hollow multilayer containers obtained in Example 14 and Comparative Example 5 were crushed into flakes using a crusher with a mesh diameter of 8 mm, and the flakes were washed with water. Then, using a floss separator CFS-150 (Acoze Co., Ltd.), the material with a heavy specific gravity that fell onto the bottom tray was recovered at a feed rate of 10 kg / hr, a suction blower of 35 Hz, and a secondary blower of 30 Hz. Finally, the crushed material in the form of flakes that fell onto the bottom tray was recovered as recycled polyester.

[0449] The recovered recycled polyester was extruded using a twin-screw extruder (Toshiba Machinery, TEM26SX) at a heater temperature of 270°C and a discharge speed of 20 kg / hour, formed into a strand, and then cut with a pelletizer while cooling in a water bath to form pellets.

[0450] Crystallization / Solid-state Polymerization Process

[0451] The pellets obtained from the above assembly process were heated at 200°C for 7 hours under a vacuum with a reduced pressure of 1 torr or less. The pellets were removed after heat treatment, and the yellowness Δb * , greenness Δa * It was evaluated. The results are shown in Table 3.

[0452] [Table 3]

[0453]

[0454] As shown in Table 3, the multilayer container of Example 14 was able to suppress yellowing of the recycled polyester even when the polyamide layer was removed during recycling by adding a small amount of yellowing inhibitor to the polyamide layer. In the multilayer container of Comparative Example 5, by adding the yellowing inhibitor to the polyester layer, when the polyamide layer was removed during recycling, the quantitative balance between the polyamide resin contained in the recycled polyester and the yellowing inhibitor was disrupted, and Δb * The value has increased.

Claims

Claim 1 A multilayer container having a polyester layer containing a polyester resin (X), and a polyamide layer containing a polyamide resin (Y), a yellowing inhibitor (A), and an oxidation promoter (B), wherein the content of the polyamide resin (Y) is 0.05 to 7.0 mass% relative to the total amount of the polyamide layer and the total polyester layer, the yellowing inhibitor (A) is a dye, and the content of the yellowing inhibitor (A) is 1 to 30 ppm relative to the total amount of the polyamide layer and the total polyester layer. Claim 2 A multilayer container according to claim 1, wherein the polyester resin (X) has a constituent unit derived from a dicarboxylic acid containing 80 mol% or more of a constituent unit derived from terephthalic acid, and a constituent unit derived from a diol containing 80 mol% or more of a constituent unit derived from ethylene glycol. Claim 3 A multilayer container according to claim 1, wherein the polyamide resin (Y) has a constituent unit derived from a diamine containing 80 mol% or more of a constituent unit derived from xylylenediamine and a constituent unit derived from a dicarboxylic acid containing 80 mol% or more of a constituent unit derived from adipic acid. Claim 4 A multilayer container in which, in claim 1, the oxidation promoter (B) is a compound containing a transition metal. Claim 5 A multilayer container according to claim 4, wherein the transition metal is at least one selected from the group consisting of cobalt, iron, manganese, and nickel. Claim 6 A multilayer container in which, in claim 1, the yellowing inhibitor (A) is an anthraquinone-based dye. Claim 7 A multilayer container according to claim 1, wherein the polyamide layer further comprises a greening inhibitor (C). Claim 8 A multilayer container according to claim 7, wherein the greening inhibitor (C) is at least one selected from the group consisting of anthraquinone dyes and azo dyes. Claim 9 A multilayer container according to claim 1, wherein the polyamide layer further comprises a polyester resin (Z). Claim 10 A multilayer container according to claim 9, wherein the content of polyester resin (Z) in the polyamide layer is 5 to 70 mass%. Claim 11 In paragraph 1, a multilayer container in which the multilayer container is a multilayer hollow container. Claim 12 A multilayer container according to claim 1, wherein the multilayer container has a 2 to 5-layer structure and the outermost layer is a polyester layer. Claim 13 A multilayer container according to claim 1, wherein the multilayer container has a 3 to 5-layer structure, and the outermost layer and the innermost layer are polyester layers. Claim 14 A method for manufacturing a multilayer container having a polyester layer containing a polyester resin (X) and a polyamide layer containing a polyamide resin (Y), a yellowing inhibitor (A), and an oxidation accelerator (B), wherein the content of the polyamide resin (Y) is 0.05 to 7.0 mass% relative to the total amount of the polyamide layer and the total polyester layer, the yellowing inhibitor (A) is a dye, and the content of the yellowing inhibitor (A) is 1 to 30 ppm relative to the total amount of the polyamide layer and the total polyester layer, comprising: a process 1 of preparing a polyamide resin mixture by mixing the polyamide resin (Y), the yellowing inhibitor (A), and the oxidation accelerator (B); a process 2 of obtaining a multilayer preform by co-injection molding the polyamide resin mixture and a polyester resin composition containing the polyester resin (X); and the multilayer preform A method for manufacturing a multilayer container comprising a blow molding process 3. Claim 15 A method for manufacturing a multilayer container, wherein, in claim 14, a greening inhibitor (C) is additionally mixed in process 1. Claim 16 A method for manufacturing a multilayer container, wherein, in claim 14 or 15, a polyester resin (Z) is additionally mixed in process 1. Claim 17 A method for manufacturing a multilayer container according to claim 14 or 15, wherein in process 1, a polyamide resin or polyester resin, a yellowing inhibitor (A) and an oxidation promoter (B) are kneaded and then mixed with a polyamide resin (Y). Claim 18 A method for manufacturing a multilayer container according to claim 14 or 15, wherein the oxidation promoter (B) is a compound containing a transition metal. Claim 19 A method for manufacturing a multilayer container according to claim 18, wherein the transition metal is at least one selected from the group consisting of cobalt, iron, manganese, and nickel. Claim 20 A method for manufacturing a multilayer container according to claim 14 or 15, wherein the yellowing inhibitor (A) is an anthraquinone-based dye. Claim 21 A method for manufacturing a multilayer container according to claim 15, wherein the greening inhibitor (C) is at least one selected from the group consisting of anthraquinone dyes and azo dyes. Claim 22 A method for manufacturing recycled polyester having a process for recovering polyester from a multilayer container described in any one of claims 1 to 13. Claim 23 A method for manufacturing recycled polyester according to claim 22, comprising a process of removing all or part of the polyamide layer from a multilayer container to recover the polyester. Claim 24 A method for manufacturing recycled polyester according to claim 23, wherein the removal of the polyamide layer is performed by balloon separation after crushing the multilayer container. Claim 25 A method for manufacturing recycled polyester according to claim 22, wherein, after a process for recovering polyester, one or more processes selected from a crystallization process and a solid-state polymerization process are performed.

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