Multilayer structure and retort packaging material using the same

Abstract

A multilayer structure which contains at least a barrier resin layer (X) and an inorganic barrier layer (Y) that is arranged adjacent to the barrier resin layer (X), while having a thickness of 500 nm or less, and which is characterized in that: the layer (X) is formed of a resin composition (x) that contains an ethylene-vinyl alcohol copolymer (A) and a polyamide (B) at a mass ratio (A / B) of from 55 / 45 to 98 / 2; and the ethylene-vinyl alcohol copolymer (A) has an ethylene content of from 20% by mole to 46% by mole and a saponification degree of 90% by mole or more. Consequently, the present invention provides: a multilayer structure which has excellent gas barrier properties and excellent appearance even if a bending process is performed after a stretching process or a retort process; and a packaging material for retort, said packaging material using this multilayer structure.

Description

[Technical Field]

[0001] The present invention relates to a multilayer structure having at least a barrier resin layer made of a resin composition containing an ethylene-vinyl alcohol copolymer and a polyamide, and an inorganic barrier layer laminated adjacent to the barrier resin layer, as well as a retort packaging material using the same, and a method for recovering the multilayer structure and a recovery composition containing the recovered multilayer structure. [Background technology]

[0002] Packaging materials for long-term food preservation often require gas barrier properties, including oxygen barrier properties. Using packaging materials with high gas barrier properties can suppress oxidation of food by oxygen and the growth of microorganisms. As a way to further extend the shelf life of food, there has been an increase in retort foods, which are processed by filling the packaging material with hot water sterilization under pressure (hereinafter sometimes simply abbreviated as retort processing). Gas barrier layers for retort packaging materials are required to have resistance to hot water treatment (hereinafter sometimes simply abbreviated as retort resistance), and gas barrier films made by laminating a transparent vapor-deposited layer of silicon dioxide or aluminum oxide on a highly heat-resistant polyester film are commonly used. When using aluminum foil, light shielding properties can be provided in addition to gas barrier properties, and when using gas barrier films laminated with a vapor-deposited layer of silicon dioxide or aluminum oxide, visibility of the contents can be provided (Patent Documents 1 and 2).

[0003] Ethylene-vinyl alcohol copolymer (hereinafter sometimes abbreviated as EVOH), which is widely used as a gas barrier resin in packaging materials, exhibits gas barrier properties through crystallization and densification by hydrogen bonding between hydroxyl groups in the molecule. Furthermore, resin compositions produced by mixing EVOH and polyamide (hereinafter sometimes abbreviated as PA) have improved retort resistance compared to EVOH alone and are preferably used as retort packaging materials (Patent Document 3). In addition, resin compositions produced by mixing specific modified EVOH and polyamide have been reported to have excellent retort resistance and flexural resistance (Patent Document 4).

[0004] In recent years, due to environmental and waste issues, there has been a growing global demand for so-called post-consumer recycling (hereinafter sometimes simply abbreviated as recycling), which involves collecting and recycling packaging materials consumed in the market. In recycling, the general process is to cut the collected packaging materials, separate and wash them if necessary, and then melt and mix them using an extruder.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Summary of the Invention

Problems to be Solved by the Invention

[0006] However, while a gas barrier film laminated with a transparent vapor deposition layer can maintain excellent gas barrier properties even after retort processing, it is prone to a decrease in gas barrier properties due to stretching or bending, and there is a concern that the quality of the food to be packaged may vary. Also, although EVOH exhibits high gas barrier properties in a dry state, in a moisture-absorbed state such as after retort processing, the hydrogen bonds are relaxed and the gas barrier properties decrease, so there may be a limitation in extending the edible period of retort foods. On the other hand, aluminum foil and polyester film, which are widely used in conventional retort packaging materials, are difficult to be uniformly mixed with other components in the melting and mixing process when recycled, which has been an obstacle to recycling.

[0007] In view of these circumstances, the first object of the present invention is to provide a multilayer structure that has excellent gas barrier properties and appearance even after bending treatment following stretching or retorting, and a retort packaging material using the same. The second object of the present invention is to provide a multilayer structure that has even better recyclability in addition to the above properties, and a method for recovering the same. [Means for solving the problem]

[0008] The inventors have found that a multilayer structure having a resin layer made of a resin composition containing specific EVOH and PA, and an inorganic layer represented by vapor deposition, laminated adjacently, exhibits excellent gas barrier properties and appearance even after bending treatment following stretching or retort treatment. Furthermore, by specifying the materials and composition used in the multilayer structure, the inventors have found that, in addition to the above properties, the structure also exhibits excellent recyclability, thus completing the present invention. In other words, the above problem is: [1] A multilayer structure having at least a barrier resin layer (X) and an inorganic barrier layer (Y) adjacent to the barrier resin layer (X) with a thickness of 500 nm or less, wherein layer (X) is made of a resin composition (x) containing ethylene-vinyl alcohol copolymer (A) and polyamide (B) in a mass ratio (A / B) of 55 / 45 to 98 / 2, and the ethylene content of the ethylene-vinyl alcohol copolymer (A) is 20 to 46 mol%, and the degree of saponification is 90 mol% or more; [2] The ethylene-vinyl alcohol copolymer (A) is a modified ethylene-vinyl alcohol copolymer (A2) represented by the following formula (I), wherein the content (mol%) of a, b, and c relative to the total monomer units satisfies the following formulas (1) to (3), and the degree of saponification defined by the following formula (4) is 90 mol% or more, in the multilayer structure of [1]; [ka] [In formula (I), R 1 , R 2 , R 3 and R 4Each of these independently represents a hydrogen atom or an alkyl group having 1 to 10 carbon atoms, and the alkyl group may contain a hydroxyl group, an alkoxy group, or a halogen atom. Each of X, Y, and Z independently represents a hydrogen atom, a formyl group, or an alkanoyl group having 2 to 10 carbon atoms. 20 ≤ a ≤ 46 (1) 0.3 ≤ c ≤ 10 (2) [100-(a+c)]×0.9≦b≦[100-(a+c)] (3) Degree of saponification = [(Total number of moles of hydrogen atoms among X, Y, and Z) / (Total number of moles of X, Y, and Z)] × 100 (4) [3] A multilayer structure of [1] or [2] wherein the resin composition (x) contains 20 to 400 ppm of at least one polyvalent metal ion (C) selected from the group consisting of magnesium ions, calcium ions, and zinc ions; [4] A multilayer structure of any of [1] to [3], wherein the barrier resin layer (X) is a single-layer film with a thickness of 8 to 40 μm; [5] A multilayer structure of [4] obtained by biaxially stretching a single-layer film; [6] A multilayer structure of any of [1] to [3], wherein the barrier resin layer (X) is one layer of a co-extruded film consisting of two or more layers including the barrier resin layer (X), the thickness of the co-extruded film is 8 to 120 μm, and the thickness of the barrier resin layer (X) is 0.5 to 20 μm; [7] A multilayer structure of [6] obtained by biaxial stretching of a co-extruded film; [8] A multilayer structure of [6] or [7] in which layers other than the barrier resin layer (X) of the co-extruded film are layers mainly composed of polypropylene resin; [9] A multilayer structure of any of [1] to [8] that does not have a layer mainly composed of a resin with a melting point of less than 140°C, a layer mainly composed of a resin with a melting point of 240°C or higher, or a metal layer with a thickness of 1 μm or more;

[10] A multilayer structure of any of the following types [1] to [9], wherein the ratio of the total thickness of the polypropylene resin-based layer to the total thickness of the multilayer structure is 0.75 or greater; Retort packaging material having any of the multilayer structures described in

[11] [1] to

[10] ;

[12] Retort packaging material of

[11] , wherein at least one barrier resin layer (X) is located on the outer side of the inorganic barrier layer (Y);

[13] The oxygen permeation rate after retort treatment at 125°C for 60 minutes (under conditions of 20°C and 65% RH) was 10 cc / (m³). 2 Retort packaging materials of

[11] or

[12] that are less than 1 day·atm;

[14] Retort packaging material of any of

[11] to

[13] , having a light transmittance of 80% or more at a wavelength of 600 nm after retort treatment at 125°C for 60 minutes; A recovered composition comprising recovered material of any of the multilayer structures

[15] [1] to

[10] ; A method for recovering a multilayer structure, comprising crushing one of the multilayer structures described in

[16] [1] to

[10] and then melt-molding it; This is solved by providing [the solution]. [Effects of the Invention]

[0009] The multilayer structure of the present invention is preferable for use as a retort packaging material because it retains excellent gas barrier properties and appearance even after bending treatment following stretching or retort treatment. Furthermore, the multilayer structure of the present invention exhibits excellent uniformity when melt-molded after crushing, and suppresses blemishes and discoloration, thus providing a retort packaging material with high recyclability. [Modes for carrying out the invention]

[0010] Embodiments of the present invention will be described below. In the following description, specific materials (compounds, etc.) that exhibit particular functions may be given as examples, but the present invention is not limited to embodiments using such materials. Furthermore, unless otherwise specified, the materials described may be used alone or in combination.

[0011] <Resin composition (x) and barrier resin layer (X)> The multilayer structure of the present invention has a barrier resin layer (X) made of a resin composition (x) containing EVOH (A) and PA (B) in a mass ratio (A / B) of 55 / 45 to 98 / 2. Although the gas barrier properties of the resin composition (x) are relatively reduced when it is hygroscopic, it has excellent gas barrier properties, retort resistance, stretch resistance, and flex resistance when dry. Therefore, a multilayer structure having a barrier resin layer (X) made of the resin composition (x) is preferably used as a component of retort packaging materials. Furthermore, the resin composition (x) has excellent thermal stability, allowing for stable melt molding over long periods of time. In order to balance the above properties at a high level, the lower limit of the mass ratio (A / B) of EVOH (A) to PA (B) must be 55 / 45, preferably 65 / 35, and may also be 78 / 22. When melt molding processability is particularly important, the lower limit of the mass ratio (A / B) of EVOH (A) to PA (B) may be preferably 83 / 17. On the other hand, the upper limit of the mass ratio (A / B) of EVOH(A) to PA(B) must be 98 / 2, preferably 96 / 4, and may also be 93 / 7. When retort resistance is particularly important, the upper limit of the mass ratio (A / B) of EVOH(A) to PA(B) may be preferably 87 / 13. If the mass ratio (A / B) is less than 55 / 45, thickening and gelation are likely to occur during melt molding of the resin composition (x) or the pulverized material of the resulting multilayer structure. On the other hand, if the mass ratio (A / B) exceeds 98 / 2, the gas barrier properties may decrease or the appearance may deteriorate after stretching or bending. Furthermore, since the resin composition (x) has excellent secondary processability, it can be applied to various secondary processes such as uniaxial stretching, biaxial stretching, and drawing, and in particular, when the barrier resin layer (X) is uniaxially stretched or biaxially stretched, the gas barrier properties and mechanical properties of the multilayer structure of the present invention can be further improved. From the viewpoint of suppressing anisotropy in mechanical properties, biaxial stretching is more preferable. Furthermore, since the resin composition (x) can be easily melt-mixed with polyolefin resins such as polyethylene and polypropylene, it is possible to provide a retort packaging material with excellent recyclability.Furthermore, the total content of EVOH(A) and PA(B) in the resin composition (x) is preferably 70% by mass or more, more preferably 90% by mass or more, and even more preferably 95% by mass or more.

[0012] <EVOH(A)> EVOH(A) is typically obtained by saponifying an ethylene-vinyl ester copolymer, which is obtained by polymerizing ethylene and vinyl ester. The ethylene unit content of EVOH(A) is 20 to 46 mol%. If the ethylene unit content is less than 20 mol%, the melt moldability, secondary processability, and hot water resistance of the resin composition (x) and the resulting multilayer structure may deteriorate. The ethylene unit content is preferably 25 mol% or more, and more preferably 30 mol% or more. On the other hand, if the ethylene unit content exceeds 46 mol%, the gas barrier properties of the resin composition (x) may be insufficient, and the appearance of the resulting multilayer structure after retort treatment may deteriorate. The ethylene unit content is preferably 40 mol% or less. Furthermore, the degree of saponification of EVOH(A) is 90 mol% or more. The degree of saponification refers to the ratio of vinyl alcohol units to the total number of vinyl alcohol units and vinyl ester units in EVOH(A). When the degree of saponification is 90 mol% or more, the gas barrier properties of the resin composition (x) and the resulting multilayer structure are improved. The degree of saponification is preferably 95 mol% or higher, and more preferably 99 mol% or higher. The ethylene unit content and degree of saponification of EVOH(A) are determined by NMR measurement. EVOH(A) may consist of two or more types of EVOH with different ethylene unit content and degrees of saponification.

[0013] EVOH(A) may contain other monomer units other than ethylene, vinyl esters, and vinyl alcohols, as long as they do not impair the effects of the present disclosure. The content of other monomer units is preferably 5% by mass or less, more preferably 3% by mass or less, even more preferably 1% by mass or less, and particularly preferably substantially absent. Other monomers of this kind include, for example, α-olefins such as propylene, n-butene, isobutylene, and 1-hexene; acrylic acid and its salts; unsaturated monomers having an acrylic acid ester group; methacrylic acid and its salts; unsaturated monomers having a methacrylic acid ester group; acrylamide, N-methylacrylamide, N-ethylacrylamide, N,N-dimethylacrylamide, diacetoneacrylamide, acrylamidepropanesulfonic acid and its salts, acrylamidepropyldimethylamine and its salts (e.g., quaternary salts); methacrylamide, N-methylmethacrylamide, N-ethylmethacrylamide, methacrylamidepropanesulfonic acid and its salts, methacrylamidepropyldimethylamine and its salts (e.g., quaternary salts); methyl vinyl ether, etc. Examples include vinyl ethers such as butyl vinyl ether, n-propyl vinyl ether, i-propyl vinyl ether, n-butyl vinyl ether, i-butyl vinyl ether, t-butyl vinyl ether, dodecyl vinyl ether, stearyl vinyl ether, and 2,3-diacetoxy-1-vinyloxypropane; vinyl cyanides such as acrylonitrile and methacrylonitrile; vinyl halides such as vinyl chloride and vinyl fluoride; vinylidenes such as vinylidene chloride and vinylidene fluoride; allyl compounds such as allyl acetate, 2,3-diacetoxy-1-allyloxypropane, and allyl chloride; unsaturated dicarboxylic acids such as maleic acid, itaconic acid, and fumaric acid, and their salts or esters; vinylsilane compounds such as vinyltrimethoxysilane; and isopropenyl acetate.

[0014] The MFR (at 210°C and under a load of 2.16 kg) of EVOH (A) is preferably 0.5 to 50 g / 10 min. The lower limit of the MFR of EVOH (A) is more preferably 1 g / 10 min, and even more preferably 2 g / 10 min. On the other hand, the upper limit of the MFR of EVOH (A) is more preferably 30 g / 10 min, and even more preferably 15 g / 10 min. When the MFR of EVOH (A) is within the above range, the melt moldability of the resin composition (x) is improved.

[0015] <Modified EVOH (A2)> EVOH (A) may be a modified ethylene-vinyl alcohol copolymer (A2) represented by the following formula (I). However, the contents (mol%) of a, b, and c with respect to all monomer units satisfy the following formulas (1) to (3), and the saponification degree defined by the following formula (4) is 90 mol% or more.

[0016] [Chemical formula]

[0017] [In formula (I), R 1 , R 2 , R 3 and R 4 each independently represent a hydrogen atom or an alkyl group having 1 to 10 carbon atoms, and the alkyl group may contain a hydroxyl group, an alkoxy group, or a halogen atom. X, Y, and Z each independently represent a hydrogen atom, a formyl group, or an alkanoyl group having 2 to 10 carbon atoms.]

[0018] 20 ≤ a ≤ 46 (1) 0.3 ≤ c ≤ 10 (2) [100 - (a + c)] × 0.9 ≤ b ≤ [100 - (a + c)] (3) Saponification degree = [(total number of moles of those which are hydrogen atoms among X, Y, and Z) / (total number of moles of X, Y, and Z)] × 100 (4)

[0019] Modified EVOH(A2), in addition to ethylene and vinyl alcohol units, has monomer units with a 1,3-diol structure in the main chain of the copolymer. Compared to EVOH without these monomer units, it has reduced crystallinity, improving stretch resistance, bending resistance, and secondary processability. Furthermore, since the crystallization rate is also reduced compared to EVOH without these monomer units, the interlayer adhesion of multilayer structures having layers made of modified EVOH(A2) can also be improved. Moreover, the strong hydrogen bonding force of the 1,3-diol structure in modified EVOH(A2) can mitigate the decrease in gas barrier properties caused by reduced crystallinity. In addition, the multilayer structure of the present invention containing modified EVOH(A2) has a high recovery rate from deformation and dimensional changes caused by stretching and bending treatments, and it is estimated that it can reduce defects in the inorganic barrier layer (Y), described later, caused by stretching and bending treatments.

[0020] In equation (I), R 1 , R 2 , R 3 and R 4 Each of these independently represents a hydrogen atom or an alkyl group having 1 to 10 carbon atoms. 1 , R 2 , R 3 and R 4 These groups may be the same or different. The structure of the alkyl group is not particularly limited and may have a branched or cyclic structure in part. Furthermore, the alkyl group may contain a hydroxyl group, an alkoxy group, or a halogen atom. 1 , R 2 , R 3 and R 4 Preferably, the alkyl group is a hydrogen atom or an alkyl group having 1 to 5 carbon atoms, with a hydrogen atom being more preferable. Suitable examples of the alkyl group include linear or branched alkyl groups such as methyl group, ethyl group, n-propyl group, isopropyl group, n-butyl group, isobutyl group, tert-butyl group, and pentyl group.

[0021] In formula (I), X, Y, and Z each independently represent a hydrogen atom, a formyl group, or an alkanoyl group having 2 to 10 carbon atoms. When X, Y, or Z is a hydrogen atom, formula (I) has a hydroxyl group, and when X, Y, or Z is a formyl group or an alkanoyl group, formula (I) has an ester group. The alkanoyl group is preferably an alkanoyl group having 2 to 5 carbon atoms, and suitable examples include acetyl groups, propanoyl groups, and butanoyl groups. Among these, the acetyl group is particularly preferred. It is preferable that X, Y, and Z are all hydrogen atoms or mixtures containing hydrogen atoms.

[0022] Monomeric units containing X are usually obtained by saponifying vinyl esters. Therefore, it is preferable that X is a mixture of hydrogen atoms and a formyl group or an alkanoyl group having 2 to 10 carbon atoms. Considering the availability and manufacturing cost of the monomer (vinyl acetate), it is particularly preferable that X is a mixture of hydrogen atoms and an acetyl group.

[0023] On the other hand, monomer units containing Y and Z can also be produced by copolymerizing and then saponifying unsaturated monomer units having a 1,3-diester structure, or by directly copolymerizing unsaturated monomer units having a 1,3-diol structure. Therefore, Y and Z may consist solely of hydrogen atoms, or a mixture of hydrogen atoms with a formyl group or an alkanoyl group having 2 to 10 carbon atoms, or more preferably, a mixture of hydrogen atoms with an acetyl group.

[0024] Modified EVOH(A2) satisfies the following formulas (1) to (3) in terms of the content (mol%) of a, b, and c relative to the total monomer units. 20 ≤ a ≤ 46 (1) 0.3 ≤ c ≤ 10 (2) [100-(a+c)]×0.9≦b≦[100-(a+c)] (3)

[0025] 'a' represents the content (mol%) of ethylene units relative to the total monomer units, and is between 20 and 46 mol%. If the ethylene unit content is less than 20 mol%, the melt moldability, secondary processability, and hot water resistance of the resin composition (x) and the resulting multilayer structure may deteriorate. 'a' is preferably 25 mol% or more, and more preferably 30 mol% or more. On the other hand, if the ethylene unit content exceeds 46 mol%, the gas barrier properties of the resin composition (x) may be insufficient, and the appearance of the resulting multilayer structure after retort treatment may deteriorate. 'a' is preferably 40 mol% or less.

[0026] c represents the content (mol%) of monomer units including Y and Z, which are shown at the right end of formula (I), relative to the total monomer units, and is between 0.3 and 10 mol%. When c is within the above range, the resin composition (x) exhibits excellent stretch resistance, flexural resistance, and secondary processability, and in particular, the resulting multilayer structure exhibits excellent gas barrier properties even when flexed after retort treatment. c is preferably 0.8 mol% or more, and more preferably 1.3 mol% or more. c is preferably 7 mol% or less, and more preferably 4 mol% or less.

[0027] b represents the content (mol%) of vinyl alcohol units and vinyl ester units relative to the total monomer units. This satisfies the following formula (3). [100-(a+c)]×0.9≦b≦[100-(a+c)] (3) In other words, in modified EVOH(A2), more than 90% of the monomer units other than the ethylene units and the monomer units containing Y and Z shown at the right end of formula (I) are vinyl alcohol units or vinyl ester units. If formula (3) is not satisfied, the gas barrier properties of the resin composition (x) and the resulting multilayer structure will be insufficient. Preferably, the following formula (3') is satisfied, and more preferably, the following formula (3") is satisfied. [100-(a+c)]×0.95≦b≦[100-(a+c)] (3') [100-(a+c)]×0.98≦b≦[100-(a+c)] (3”)

[0028] The degree of saponification in modified EVOH(A2), as defined by formula (4) below, is 90 mol% or higher. Degree of saponification = [(Total number of moles of hydrogen atoms among X, Y, and Z) / (Total number of moles of X, Y, and Z)] × 100 (4) Here, "total number of moles of hydrogen atoms among X, Y, and Z" refers to the number of moles of hydroxyl groups, and "total number of moles of X, Y, and Z" refers to the total number of moles of hydroxyl groups and ester groups. If the degree of saponification is less than 90 mol%, not only will sufficient gas barrier properties not be obtained in the resin composition (x) and the resulting multilayer structure, but thermal stability will also be insufficient, making it easier for gels and lumps to form during melt molding. A degree of saponification of 95 mol% or more is preferred, and 99 mol% or more is more preferred.

[0029] The content and degree of saponification of the monomer units a, b, and c of denatured EVOH(A2) can be determined by NMR measurement. If denatured EVOH(A2) consists of a mixture of two or more different types of denatured EVOH, the content and degree of saponification of the monomer units a, b, and c can be similarly determined by NMR measurement for the mixture of denatured EVOH.

[0030] The method for producing modified EVOH(A2) is not particularly limited. For example, one method involves radical polymerization of ethylene, a vinyl ester represented by the following formula (II), and an unsaturated monomer represented by the following formula (III) to obtain a modified ethylene-vinyl ester copolymer represented by the following formula (IV), and then saponifying it.

[0031] [ka]

[0032] In formula (II), R 5The group represents a hydrogen atom or an alkyl group having 1 to 9 carbon atoms. The number of carbon atoms in the alkyl group is preferably 1 to 4. Examples of vinyl esters represented by formula (II) include vinyl formate, vinyl acetate, vinyl propionate, vinyl butyrate, vinyl isobutyrate, vinyl pivalate, vinyl versatate, and vinyl caproate. From an economic standpoint, vinyl acetate is particularly preferred.

[0033] [ka]

[0034] In formula (III), R 1 , R 2 , R 3 and R 4 This is the same as equation (I). R 6 and R 7 Each of these independently represents a hydrogen atom or an alkyl group having 1 to 9 carbon atoms. The number of carbon atoms in the alkyl group is preferably 1 to 4. Examples of unsaturated monomers represented by formula (III) include 2-methylene-1,3-propanediol diacetate (1,3-diacetoxy-2-methylenepropane), 2-methylene-1,3-propanediol dipropionate, and 2-methylene-1,3-propanediol dibutyrate. Among these, 2-methylene-1,3-propanediol diacetate is preferred because it is easy to manufacture. In the case of 2-methylene-1,3-propanediol diacetate, R 1 , R 2 , R 3 and R 4 is a hydrogen atom, and R 6 and R 7 This is a methyl group.

[0035] [ka]

[0036] In formula (IV), R 1 , R 2 , R 3 , R 4 , R 5 , R6 , R 7 , a, b, and c are the same as in formulas (I) to (III). The modified ethylene-vinyl ester copolymer thus obtained is then subjected to saponification.

[0037] Alternatively, instead of copolymerizing the unsaturated monomer shown in formula (III) above, an unsaturated monomer shown in formula (V) below may be copolymerized. In this case, only the units derived from the unsaturated monomer shown in formula (II) above will be saponified by the saponification treatment.

[0038] [ka]

[0039] In formula (V), R 1 , R 2 , R 3 and R 4 This is the same as equation (I). An example of an unsaturated monomer represented by equation (V) is 2-methylene-1,3-propanediol.

[0040] The unsaturated monomers represented by formulas (III) and (V) used in this invention exhibit high copolymerization reactivity with vinyl ester monomers, thus facilitating copolymerization. Therefore, it is easy to achieve a high degree of modification and polymerization in the resulting modified EVOH(A2). Furthermore, even if the polymerization reaction is stopped at a low polymerization rate, the amount of unreacted unsaturated monomer remaining at the end of polymerization is small, making it superior in terms of environmental impact and cost. In this respect, the unsaturated monomers represented by formulas (III) and (V) are superior to other monomers with only one carbon atom having a functional group at the allyl position, such as allyl glycidyl ether and 3,4-diacetoxy-1-butene. Here, the unsaturated monomer represented by formula (III) is more reactive than the unsaturated monomer represented by formula (V).

[0041] When copolymerizing ethylene with a vinyl ester represented by formula (II) and an unsaturated monomer represented by formula (III) or (V) to produce modified EVOH(A2), the polymerization method can be batch polymerization, semi-batch polymerization, continuous polymerization, or semi-continuous polymerization. Furthermore, known polymerization methods such as bulk polymerization, solution polymerization, suspension polymerization, and emulsion polymerization can be employed. Bulk polymerization or solution polymerization, which proceed in a solvent-free environment or in a solvent such as alcohol, is commonly used. When obtaining a modified ethylene-vinyl ester copolymer with a high degree of polymerization, emulsion polymerization is one option.

[0042] The solvent used in solution polymerization is not particularly limited, but alcohols are preferably used, and lower alcohols such as methanol, ethanol, and propanol are more preferably used. The amount of solvent used in the polymerization reaction solution should be selected considering the viscosity-average degree of polymerization of the target modified EVOH(A2) and the chain transfer of the solvent, and the weight ratio of the solvent to the total monomers (solvent / total monomers) in the reaction solution should be selected from the range of 0.01 to 10, preferably from the range of 0.05 to 3.

[0043] When copolymerizing ethylene with a vinyl ester represented by formula (II) and an unsaturated monomer represented by formula (III) or (V), the polymerization initiator used is selected from known polymerization initiators, such as azo initiators, peroxide initiators, and redox initiators, depending on the polymerization method. Examples of azo initiators include 2,2'-azobisisobutyronitrile, 2,2'-azobis(2,4-dimethylvaleronitrile), and 2,2'-azobis(4-methoxy-2,4-dimethylvaleronitrile). Examples of peroxide-based initiators include peroxide compounds such as diisopropyl peroxydicarbonate, di-2-ethylhexyl peroxydicarbonate, and diethoxyethyl peroxydicarbonate; perester compounds such as t-butyl peroxyneodecanate, α-cumyl peroxyneodecanate, and acetyl peroxide; acetylcyclohexyl sulfonyl peroxide; and 2,4,4-trimethylpentyl-2-peroxyphenoxyacetate. Potassium persulfate, ammonium persulfate, and hydrogen peroxide may be used in combination with the above initiators. Redox initiators are polymerization initiators that combine the above peroxide-based initiators with reducing agents such as sodium bisulfite, sodium bicarbonate, tartaric acid, L-ascorbic acid, and longalit. The amount of polymerization initiator used cannot be determined in general as it varies depending on the polymerization catalyst, but it is adjusted according to the polymerization rate. The amount of polymerization initiator used is preferably 0.01 to 0.2 mol%, and more preferably 0.02 to 0.15 mol%, relative to the vinyl ester monomer. The polymerization temperature is not particularly limited, but room temperature to about 150°C is suitable, and preferably 40°C or higher and below the boiling point of the solvent used.

[0044] When copolymerizing ethylene with a vinyl ester represented by formula (II) and an unsaturated monomer represented by formula (III) or (V), copolymerization may be carried out in the presence of a chain transfer agent, provided that the effects of the present invention are not inhibited. Examples of chain transfer agents include aldehydes such as acetaldehyde and propionaldehyde; ketones such as acetone and methyl ethyl ketone; mercaptans such as 2-hydroxyethanethiol; and phosphinates such as sodium phosphinate monohydrate. Among these, aldehydes and ketones are preferably used. The amount of chain transfer agent added to the polymerization reaction solution is determined according to the chain transfer coefficient of the chain transfer agent and the degree of polymerization of the desired modified ethylene-vinyl ester copolymer, but generally, 0.1 to 10 parts by mass per 100 parts by mass of vinyl ester monomer is preferred.

[0045] The modified ethylene-vinyl ester copolymer obtained in this way can be saponified to obtain the modified EVOH(A2) used in the present invention. At this time, the vinyl ester units in the copolymer are converted to vinyl alcohol units. In addition, the ester bond derived from the unsaturated monomer shown in formula (III) is simultaneously hydrolyzed and converted to a 1,3-diol structure. In this way, different types of ester groups can be hydrolyzed simultaneously in a single saponification reaction.

[0046] Known methods can be used to saponify the modified ethylene-vinyl ester copolymer. The saponification reaction is usually carried out in a solution of alcohol or aqueous alcohol. Preferably used alcohols are lower alcohols such as methanol and ethanol, with methanol being particularly preferred. The alcohol or aqueous alcohol used in the saponification reaction may also contain other solvents such as acetone, methyl acetate, ethyl acetate, and benzene, as long as they make up 40% or less of its weight. Catalysts used for saponification include alkali metal hydroxides such as potassium hydroxide and sodium hydroxide, alkaline catalysts such as sodium methylate, and acid catalysts such as mineral acids. The temperature for saponification is not limited, but a range of 20 to 120°C is preferred. If a gel-like product precipitates as saponification progresses, the product can be pulverized, washed, and dried to obtain modified EVOH(A2).

[0047] The modified EVOH(A2) used in the present invention may contain structural units derived from other monomers that are copolymerizable with ethylene, vinyl esters represented by formula (II) above, and unsaturated monomers represented by formula (III) or (V) above, as long as the effects of the present invention are not hindered. The content of other monomer units is preferably 5% by mass or less, more preferably 3% by mass or less, even more preferably 1% by mass or less, and particularly preferably substantially absent. Other monomers of this kind include, for example, α-olefins such as propylene, n-butene, isobutylene, and 1-hexene; acrylic acid and its salts; unsaturated monomers having an acrylic acid ester group; methacrylic acid and its salts; unsaturated monomers having a methacrylic acid ester group; acrylamide, N-methylacrylamide, N-ethylacrylamide, N,N-dimethylacrylamide, diacetoneacrylamide, acrylamidepropanesulfonic acid and its salts, acrylamidepropyldimethylamine and its salts (e.g., quaternary salts); methacrylamide, N-methylmethacrylamide, N-ethylmethacrylamide, methacrylamidepropanesulfonic acid and its salts, methacrylamidepropyldimethylamine and its salts (e.g., quaternary salts); methyl vinyl ether, etc. Examples include vinyl ethers such as butyl vinyl ether, n-propyl vinyl ether, i-propyl vinyl ether, n-butyl vinyl ether, i-butyl vinyl ether, t-butyl vinyl ether, dodecyl vinyl ether, stearyl vinyl ether, and 2,3-diacetoxy-1-vinyloxypropane; vinyl cyanides such as acrylonitrile and methacrylonitrile; vinyl halides such as vinyl chloride and vinyl fluoride; vinylidenes such as vinylidene chloride and vinylidene fluoride; allyl compounds such as allyl acetate, 2,3-diacetoxy-1-allyloxypropane, and allyl chloride; unsaturated dicarboxylic acids such as maleic acid, itaconic acid, and fumaric acid, and their salts or esters; vinylsilane compounds such as vinyltrimethoxysilane; and isopropenyl acetate.

[0048] <PA(B)> Specific examples of PA(B) used in the present invention include polycaproamide (nylon 6), poly-ω-aminoheptanoic acid (nylon 7), poly-ω-aminononanoic acid (nylon 9), polyundecaneamide (nylon 11), polylauryl lactam (nylon 12), polyethylenediamine adipamide (nylon 26), polytetramethylene adipamide (nylon 46), polyhexamethylene adipamide (nylon 66), polyhexamethylene sevacamide (nylon 610), and polyhexamethylene dodecamide. (Nylon 612), polyoctamethylene adipamide (Nylon 86), polydecamethylene adipamide (Nylon 106), caprolactam / lauryl lactam copolymer (Nylon 6 / 12), caprolactam / ω-aminononanoic acid copolymer (Nylon 6 / 9), caprolactam / hexamethylenediammonium adipate copolymer (Nylon 6 / 66), lauryl lactam / hexamethylenediammonium adipate copolymer (Nylon 12 / 66), ethylenediammonium adipate / hexamethylene Dienzium adipate copolymer (Nylon 26 / 66), Caprolactam / Hexamethylenediammonium adipate / Hexamethylenediammonium sebacate copolymer (Nylon 6 / 66 / 610), Ethylenediammonium adipate / Hexamethylenediammonium adipate / Hexamethylenediammonium sebacate copolymer (Nylon 26 / 66 / 610), Polyhexamethylene isophthalamide (Nylon 6I), Polyhexamethylene terephthalamide (Nylon 6T), Hex Examples include methylene isophthalamide / hexamethylene terephthalamide copolymer (nylon 6I / 6T), 11-aminoundecaneamide / hexamethylene terephthalamide copolymer, polynonameethylene terephthalamide (nylon 9T), polydecamethylene terephthalamide (nylon 10T), polyhexamethylene cyclohexylamide, polynonameethylene cyclohexylamide, or these polyamides modified with aromatic amines such as methylenebenzylamine and metaxylenediamine. Metaxylylenediammonium adipate is also an example.Among these, a polyamide resin mainly composed of caproamide is preferred from the viewpoint of particularly improving gas barrier properties and appearance after retort processing. Specifically, it is preferable that 75 mol% or more of the constituent units of PA(B) are caproamide units. In particular, from the viewpoint of compatibility with EVOH(A), it is preferable that PA(B) is nylon 6.

[0049] The degree of polymerization of PA(B) is preferably 1.7 to 5.0, and more preferably 2.0 to 5.0, based on the relative viscosity measured in accordance with JIS K6810.

[0050] The polymerization method for PA(B) can be melt polymerization, interfacial polymerization, solution polymerization, bulk polymerization, solid-phase polymerization, or a combination of these methods.

[0051] <Polyvalent metal ions (C)> The resin composition (x) preferably contains 20 to 400 ppm of at least one polyvalent metal ion (C) selected from the group consisting of magnesium ions, calcium ions, and zinc ions. Since the multilayer structure of the present invention has an inorganic barrier layer (Y) made of inorganic materials such as aluminum, alumina, and silica, when the pulverized material is melt-molded, the inorganic materials may promote the crosslinking reaction of the resin, causing thickening and gelation. However, by including a certain amount of polyvalent metal ions (C), thickening, gelation, and adhesion of the resin to the screw are suppressed. In particular, the resin composition (x) preferably contains magnesium ions or calcium ions as the polyvalent metal ions (C), and more preferably contains magnesium ions.

[0052] Furthermore, the polyvalent metal ion (C) is preferably included as a carboxylate salt or hydroxide, and is more preferably included as a hydroxide from the standpoint of ease of handling during manufacturing. The carboxylic acid may be either an aliphatic carboxylic acid or an aromatic carboxylic acid, but an aliphatic carboxylic acid is preferred. Examples of aliphatic carboxylic acids include formic acid, acetic acid, propionic acid, butyric acid, lauric acid, stearic acid, myristic acid, behenic acid, and montanic acid. Among these, acetic acid is preferred from the viewpoint of ease of availability and improved thermal stability during melt molding of the resulting multilayer structure, as well as suppression of bleed. In addition, the polyvalent metal ion (C) can also be included as a salt of a polyvalent carboxylic acid, as described later.

[0053] To effectively suppress thickening, gelation, and resin adhesion to the screw of the resin composition (x), the polyvalent metal ion (C) content is more preferably 40 ppm or more, and even more preferably 100 ppm or more. When the ratio of PA(B) in the resin composition (x) is relatively high, the polyvalent metal ion (C) content may be preferably 130 ppm or more. On the other hand, in order to suppress excessive decomposition of the pulverized material of the resulting multilayer structure and to obtain a good hue for the recovered composition, the polyvalent metal ion (C) content is more preferably 300 ppm or less, and even more preferably 200 ppm or less. When the ratio of PA(B) in the resin composition (x) is relatively low, the polyvalent metal ion (C) content may be preferably 160 ppm or less.

[0054] The resin composition (x) may contain other components besides polyvalent metal ions (C), as long as the effects of the present invention are not hindered. Examples of other components include alkali metal ions, alkaline earth metal ions and transition metal ions other than polyvalent metal ions (C), carboxylic acids (monocarboxylic acids, polycarboxylic acids), phosphoric acid compounds, boron compounds, oxidation accelerators, antioxidants, plasticizers, heat stabilizers (melt stabilizers), photoinitiators, deodorizers, ultraviolet absorbers, antistatic agents, lubricants, colorants, fillers, drying agents, fillers, pigments, dyes, processing aids, flame retardants, antifogging agents, etc. In particular, from the viewpoint of improving the interlayer adhesion of the multilayer structure, it is preferable to include alkali metal ions. Furthermore, from the viewpoint of suppressing discoloration when melt-molding the resin composition (x) and the pulverized multilayer structure containing the resin composition (x), it is preferable to include carboxylic acids and / or phosphoric acid compounds. By including boron compounds, the melt viscosity of the resin composition (x) and the pulverized multilayer structure containing the resin composition (x) can be controlled.

[0055] <Alkali metal ions> The resin composition (x) preferably contains alkali metal ions. The lower limit of the alkali metal ion content is preferably 100 ppm, and more preferably 150 ppm. On the other hand, the upper limit of the alkali metal ion content is preferably 400 ppm, and more preferably 350 ppm. If the alkali metal ion content is less than 100 ppm, the interlayer adhesion of the multilayer molded article containing the layer obtained by molding the resin composition (x) may be insufficient. On the other hand, if the alkali metal ion content exceeds 400 ppm, discoloration due to thermal degradation may become a problem. Furthermore, by controlling the content ratio of alkali metal ions to carboxylic acid, which will be described later, the melt moldability and discoloration resistance of the obtained resin composition (x) can be further improved.

[0056] Examples of alkali metal ions include lithium, sodium, potassium, rubidium, and cesium ions, but sodium or potassium ions are preferred from the standpoint of industrial availability. In particular, using potassium ions can sometimes achieve a high level of both the hue of the resin composition (x) and the interlayer adhesion between the barrier resin layer (X) and the adhesive resin layer when used as a co-extruded film, as described later. These may be used individually or in combination of two or more types.

[0057] Examples of alkali metal salts that provide alkali metal ions include aliphatic carboxylates, aromatic carboxylates, carbonates, hydrochlorides, nitrates, sulfates, phosphates, and metal complexes of alkali metals such as lithium, sodium, and potassium. Among these, sodium acetate, potassium acetate, sodium phosphate, and potassium phosphate are more preferred due to their readily available availability.

[0058] <Carboxylic acid> The resin composition (x) preferably contains a carboxylic acid. The lower limit of the carboxylic acid content is preferably 50 ppm, and more preferably 100 ppm. On the other hand, the upper limit of the carboxylic acid content is preferably 400 ppm, and more preferably 350 ppm. If the carboxylic acid content is less than 50 ppm, the color resistance may be insufficient. On the other hand, if the carboxylic acid content exceeds 400 ppm, the interlayer adhesion may be insufficient, or odor may become a problem. The carboxylic acid content can be determined by extracting 10 g of the resin composition (x) with 50 ml of pure water at 95°C for 8 hours, and then titrating the resulting extract. Note that carboxylic acid present as a salt in the extract is not considered when calculating the carboxylic acid content in the resin composition (x). Furthermore, if the resin composition (x) contains acidic compounds other than carboxylic acids, the carboxylic acid content in the resin composition (x) can be determined by subtracting the contribution of those acidic compounds from the measured value obtained by titration.

[0059] The pKa of the carboxylic acid is preferably between 3.5 and 5.5. When the pKa of the carboxylic acid is within this range, the pH buffering capacity of the resulting resin composition (x) is increased, further improving melt moldability and reducing discoloration by acidic and basic substances.

[0060] The carboxylic acid may be a monovalent carboxylic acid. These may be used individually or in combination of two or more. A monovalent carboxylic acid is a compound having one carboxyl group in its molecule. Monovalent carboxylic acids with a pKa in the range of 3.5 to 5.5 and a boiling point of less than 150°C are not particularly limited, and examples include formic acid (pKa=3.77), acetic acid (pKa=4.76), propionic acid (pKa=4.85), and acrylic acid (pKa=4.25). These carboxylic acids may further have substituents such as hydroxyl groups, amino groups, and halogen atoms, as long as their boiling point is less than 150°C. Among these, acetic acid is preferred because of its high safety and ease of availability and handling.

[0061] The carboxylic acid may also be a polycarboxylic acid. If the carboxylic acid is a polycarboxylic acid, the color resistance of the resin composition (x) at high temperatures and the color resistance of the melt-molded crushed product of the resulting multilayer structure may be further improved. Furthermore, it is preferable that the polycarboxylic acid compound has three or more carboxyl groups. In this case, the color resistance may be improved more effectively. A polycarboxylic acid is a compound having two or more carboxyl groups in its molecule. In this case, it is preferable that the pKa of at least one carboxyl group is in the range of 3.5 to 5.5, for example, oxalic acid (pKa2=4.27), succinic acid (pKa1=4.20), fumaric acid (pKa2=4.44), malic acid (pKa2=5.13), glutaric acid (pKa1=4.30, pKa2=5.40), adipic acid (pKa1=4.43, pKa Examples include pKa2=5.41, pKa1=4.71, phthalic acid (pKa2=5.41), isophthalic acid (pKa2=4.46), terephthalic acid (pKa1=3.51, pKa2=4.82), citric acid (pKa2=4.75), tartaric acid (pKa2=4.40), glutamic acid (pKa2=4.07), and aspartic acid (pKa=3.90).

[0062] <Phosphate compounds> The resin composition (x) may further contain a phosphate compound. The lower limit of the phosphate compound content is preferably 5 ppm in terms of phosphate root. On the other hand, the upper limit of the phosphate compound content is preferably 100 ppm in terms of phosphate root. By including a phosphate compound within this range, discoloration of the resulting resin composition (x) and the melt-molded product of the pulverized multilayer structure may be suppressed, and the thermal stability may be improved.

[0063] As phosphate compounds, various acids such as phosphoric acid and phosphorous acid, and their salts can be used. The phosphate may be any of the first, second, or third phosphates. The cation species of the phosphate is not particularly limited, but alkali metals and alkaline earth metals are preferred. Among these, sodium dihydrogen phosphate, potassium dihydrogen phosphate, disodium hydrogen phosphate, and dipotassium hydrogen phosphate are preferred as phosphate compounds.

[0064] <Boron compounds> The resin composition (x) may further contain a boron compound. When a boron compound is included, the lower limit of its content in the resin composition (x) is preferably 50 ppm and more preferably 100 ppm in terms of boron element. On the other hand, the upper limit of the boron compound content in the resin composition (x) is preferably 400 ppm and more preferably 200 ppm in terms of boron element. Including a boron compound within this range can improve the thermal stability of the resin composition (x) and the resulting pulverized multilayer structure during melt molding, and may suppress the generation of gel and blemishes. In addition, it may improve resistance to drawdown and neck-in during film formation, and improve the mechanical properties of the resulting molded article. These effects are presumed to be due to chelate interactions between EVOH(A) and the boron compound.

[0065] Examples of boron compounds include boric acid, boric acid esters, borate salts, and boron hydride. Specifically, these include boric acid such as orthoboric acid (H3BO3), metaboric acid, and tetraboric acid; boric acid esters such as trimethyl borate and triethyl borate; and alkali metal salts or alkaline earth metal salts of the aforementioned boric acid, borate salts such as borax, etc. Among these, orthoboric acid is preferred.

[0066] <Hindered phenol compounds> The resin composition (x) may further contain a hindered phenol compound having an ester bond or an amide bond. When a hindered phenol compound is included, the content of the hindered phenol compound in the resin composition (x) is preferably 1,000 to 10,000 ppm. When the content is 1,000 ppm or more, discoloration, thickening, and gelation of the resin can be suppressed when melt-molding the pulverized multilayer structure. A content of 2,000 ppm or more of the hindered phenol compound is more preferable. On the other hand, when the content of the hindered phenol compound is 10,000 ppm or less, discoloration and bleed-out originating from the hindered phenol compound can be suppressed. A content of 8,000 ppm or less of the hindered phenol compound is more preferable.

[0067] Hindered phenol compounds have at least one hindered phenol group. A hindered phenol group is defined as a group in which a bulky substituent is bonded to at least one carbon adjacent to the carbon atom to which the hydroxyl group of phenol is bonded. Preferably, the bulky substituent is an alkyl group with 1 to 10 carbon atoms, and more preferably a t-butyl group.

[0068] Hindered phenol compounds are preferably in a solid state at or near room temperature. From the viewpoint of suppressing bleed-out of the compound, the melting point or softening temperature of the hindered phenol compound is preferably 50°C or higher, more preferably 60°C or higher, and even more preferably 70°C or higher. From a similar viewpoint, the molecular weight of the hindered phenol compound is preferably 200 or higher, more preferably 400 or higher, and even more preferably 600 or higher. On the other hand, the molecular weight is usually 2000 or lower. Furthermore, from the viewpoint of facilitating mixing with EVOH(A) and PA(B), the melting point or softening temperature of the hindered phenol compound is preferably 200°C or lower, more preferably 190°C or lower, and even more preferably 180°C or lower.

[0069] Hindered phenol compounds have either an ester bond or an amide bond. Examples of hindered phenol compounds having an ester bond include esters of an aliphatic carboxylic acid having a hindered phenol group and an aliphatic alcohol, while examples of hindered phenol compounds having an amide include amides of an aliphatic carboxylic acid having a hindered phenol group and an aliphatic amine. Among these, it is preferable that the hindered phenol compound has an amide bond.

[0070] Specific structures of hindered phenol compounds include pentaerythritol tetrakis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], marketed by BASF as Irganox 1010; stearyl 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, marketed as Irganox 1076; 2,2'-thiodiethylbis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], marketed as Irganox 1035; and 3,2'-thiodiethylbis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], marketed as Irganox 1135. Examples include octadecyl (3,5-di-tert-butyl-4-hydroxyphenyl)propanoate, bis(3-tert-butyl-4-hydroxy-5-methylbenzenepropanoate)ethylenebis(oxyethylene) sold as Irganox 245, 1,6-hexanediolbis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] sold as Irganox 259, and N,N'-hexamethylenebis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propanamide] sold as Irganox 1098. In particular, N,N'-hexamethylenebis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propanamide], which is commercially available as Irganox 1098, and pentaerythritol tetrakis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], which is commercially available as Irganox 1010, are preferred, with the former being more preferred.

[0071] The resin composition (x) may further contain thermoplastic resins other than EVOH(A) and PA(B). Examples of thermoplastic resins other than EVOH(A) and PA(B) include various polyolefins (polyethylene, polypropylene, poly-1-butene, poly-4-methyl-1-pentene, ethylene-propylene copolymer, copolymer of ethylene and α-olefin having 4 or more carbon atoms, copolymer of polyolefin and maleic anhydride, ethylene-vinyl ester copolymer, ethylene-acrylic acid ester copolymer, or modified polyolefins obtained by grafting these with unsaturated carboxylic acids or their derivatives), various polyesters (polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, etc.), polyvinyl chloride, polyvinylidene chloride, polystyrene, polyacrylonitrile, polyurethane, polycarbonate, polyacetal, polyacrylate, and modified polyvinyl alcohol resin. The content of the thermoplastic resin in the resin composition (x) is preferably less than 30% by mass, more preferably less than 10% by mass, even more preferably 5% by mass or less, and may be 1% by mass or less.

[0072] The method for producing the resin composition (x) is not particularly limited, but it can be produced by melt-kneading EVOH (A) and PA (B), and other components and additives such as polyvalent metal ions (C) as needed. The polyvalent metal ions (C) may be blended in a solid state such as powder, or as a melt, or as a solute contained in a solution or a dispersed in a dispersion. Aqueous solutions and aqueous dispersions are preferred as the solution and dispersion, respectively. For melt-kneading, known mixing or kneading equipment such as a kneader-ruder, extruder, mixing roll, or Banbury mixer can be used. The temperature range during melt-kneading can be appropriately adjusted according to the melting points of EVOH (A) and PA (B) used, and is usually 190 to 250°C.

[0073] In one embodiment of the present invention, the barrier resin layer (X) is a single-layer film made using a resin composition (x) as the main component. The method for making such a layer is not particularly limited, but it is generally made by melt extrusion using an extruder. The barrier resin layer (X) may be a single-layer film with a thickness of 8 to 40 μm, or it may be a biaxially oriented single-layer film with a thickness of 8 to 20 μm, obtained by biaxially stretching the single-layer film. In particular, from the viewpoint of exhibiting gas barrier properties even when the thickness of the barrier resin layer (X) is relatively small and improving the gas barrier properties of the resulting multilayer structure after retort treatment, it is preferable that the barrier resin layer (X) is a biaxially oriented single-layer film. The stretching method is not particularly limited, and either simultaneous stretching or sequential stretching is possible. The stretching ratio is preferably an area ratio of 8 to 12 times from the viewpoint of uniformity of thickness, gas barrier properties and mechanical strength of the resulting film. An area ratio of 12 times or less is preferred, and 11 times or less is more preferred. Furthermore, the area ratio of the stretching ratio is preferably 8 times or more, and more preferably 9 times or more. If the area ratio is less than 8 times, stretching unevenness may remain, and if it exceeds 12 times, the film may easily break during stretching. In addition, pre-moistening the raw material before stretching makes continuous stretching easier. The moisture content of the raw material before stretching is preferably 2% by mass or more, more preferably 5% by mass or more, and even more preferably 10% by mass or more. The moisture content of the raw material before stretching is preferably 30% by mass or less, more preferably 25% by mass or less, and even more preferably 20% by mass or less. If the moisture content is less than 2% by mass, stretching unevenness may remain, and especially when stretching in the width direction of the roll, the stretching ratio becomes higher in the part close to the grip that holds the film, and tearing may easily occur near the grip. On the other hand, if the moisture content exceeds 30% by mass, the elastic modulus of the stretched part is low, the difference with the unstretched part is not sufficient, and stretching unevenness may remain. The temperature used for stretching can vary depending on the moisture content of the raw material before stretching, but generally a temperature range of 50°C to 130°C is used. In particular, for simultaneous biaxial stretching, a temperature range of 70°C to 100°C yields a biaxially oriented single-layer film with minimal stretching unevenness.In sequential biaxial stretching, a biaxially oriented single-layer film with minimal stretching unevenness can be obtained by using a temperature range of 70°C to 100°C when stretching in the longitudinal direction of the roll, and 80°C to 120°C when stretching in the width direction of the roll.

[0074] In another embodiment of the present invention, the barrier resin layer (X) may also be one layer of a co-extruded film consisting of two or more layers including the barrier resin layer (X). The layers of the co-extruded film other than the barrier resin layer (X) are preferably layers mainly composed of resins other than the resin composition (x). Examples of such resins include those listed as thermoplastic resins that may be included in the resin composition (x) in addition to EVOH (A) and PA (B). From the viewpoint of excellent gas barrier properties and appearance after retort treatment of the resulting multilayer structure, and excellent recyclability of the resulting multilayer structure, it is more preferable that the layers consist mainly of polypropylene resin, and even more preferable that the layers consist only of polypropylene resin. As the polypropylene resin in the co-extruded film, either unmodified polypropylene resin or modified polypropylene resin can be used. Examples of acid-modified polypropylene resins include resins obtained by modifying polypropylene resin with maleic acid, fumaric acid, itaconic acid, maleic anhydride, or itaconic anhydride. Acid-modified polypropylene resins can be used as polypropylene adhesive resins.

[0075] The method for producing the co-extruded film is not particularly limited, but it is generally produced by a melt molding method using an extruder. In this case, the thickness of the co-extruded film is preferably 8 to 120 μm, and the thickness of the barrier resin layer (X) is preferably 1 to 20 μm. When the co-extruded film is biaxially stretched, the thickness of the co-extruded film is preferably 8 to 60 μm, and the thickness of the barrier resin layer (X) is preferably 0.5 to 10 μm, and more preferably 1 to 10 μm. The stretching method is not particularly limited, and both simultaneous stretching and sequential stretching are possible. From the viewpoint of uniformity of the thickness of the resulting film and mechanical strength, the stretching ratio is preferably an area ratio of 8 to 60 times. An area ratio of 55 times or less is preferred, and 50 times or less is more preferred. Furthermore, as a stretching ratio, an area ratio of 8 times or more is preferred, and 9 times or more is more preferred. If the area ratio is less than 8 times, stretching unevenness may remain, and if it exceeds 60 times, the film may easily break during stretching.

[0076] <Inorganic barrier layer (Y)> In the multilayer structure of the present invention, at least one inorganic barrier layer (Y) with a thickness of 500 nm or less must be adjacent to the barrier resin layer (X). The inorganic barrier layer is a layer made of inorganic materials such as metals or metal oxides, which has shielding properties against oxygen, water vapor, water during retort processing, etc. By having an inorganic barrier layer (Y) adjacent to the barrier resin layer (X), the permeation of oxygen through minute defects in the inorganic barrier layer (Y) can be effectively suppressed, and the multilayer structure of the present invention exhibits excellent gas barrier properties even after retort processing and bending processing. Furthermore, because the thickness of the inorganic barrier layer (Y) is 500 nm or less, the viscosity stability is excellent when the pulverized material of the multilayer structure of the present invention is melt-molded, and the generation of gels and lumps can be suppressed. The inorganic barrier layer (Y) is preferably either a metal vapor-deposited layer (Y1) mainly composed of aluminum, or an inorganic oxide vapor-deposited layer (Y2) mainly composed of alumina or silica. A metal vapor-deposited layer (Y1) is preferred when light-shielding properties are to be provided, but an inorganic oxide vapor-deposited layer (Y2) is preferred from the viewpoint of visibility of the contents as a packaging material and the ability to suppress the generation of gels and lumps when melt-molding crushed material.

[0077] <Metal deposition layer (Y1)> The metal vapor-deposited layer (Y1) is a layer mainly composed of aluminum. The aluminum atom content in the metal vapor-deposited layer (Y1) must be 50 mol% or more, preferably 70 mol% or more, more preferably 90 mol% or more, and even more preferably 95 mol% or more. At least one metal vapor-deposited layer (Y1) must be adjacent to the barrier resin layer (X). The average thickness of the metal vapor-deposited layer (Y1) is preferably 120 nm or less, more preferably 100 nm or less, and even more preferably 90 nm or less. Furthermore, the average thickness of the metal vapor-deposited layer (Y1) is preferably 25 nm or more, more preferably 35 nm or more, and even more preferably 45 nm or more. The average thickness of the metal vapor-deposited layer (Y1) is the average value of the thickness at any 10 points on the cross-section of the metal vapor-deposited layer (Y1) measured by electron microscope. From the viewpoint of reducing the coloration of the recovered composition of the multilayer structure, when the multilayer structure has multiple metal vapor-deposited layers (Y1), the total thickness of the metal vapor-deposited layers (Y1) is preferably 1 μm or less. When the multilayer structure of the present invention has a metal vapor deposition layer (Y1), the light transmittance at a wavelength of 600 nm can be set to 10% or less, and it exhibits excellent light shielding properties.

[0078] <Inorganic oxide vapor deposited layer (Y2)> The inorganic oxide vapor-deposited layer (Y2) is a vapor-deposited film of an inorganic oxide, such as an oxide of silicon, aluminum, magnesium, calcium, potassium, tin, sodium, boron, titanium, lead, zirconium, yttrium, etc., preferably alumina or silica. The average thickness of the inorganic oxide vapor-deposited layer (Y2) is preferably 90 nm or less, more preferably 70 nm or less, and even more preferably 50 nm or less. Furthermore, the average thickness of the inorganic oxide vapor-deposited layer (Y2) is preferably 10 nm or more, more preferably 15 nm or more, and even more preferably 20 nm or more. The average thickness of the inorganic oxide vapor-deposited layer (Y2) is the average value of the thickness at any 10 points on the cross-section of the inorganic oxide vapor-deposited layer (Y2) measured by an electron microscope. When the multilayer structure of the present invention has an inorganic oxide vapor-deposited layer (Y2), the light transmittance at a wavelength of 600 nm can be 80% or more, and the visibility of the contents when used as a packaging material is excellent. From the viewpoint of further improving visibility, a light transmittance of 90% or more at a wavelength of 600 nm is more preferable.

[0079] The inorganic barrier layer (Y) can be formed by known physical or chemical vapor deposition methods. Specifically, examples include vacuum vapor deposition, sputtering, ion plating, ion beam mixing, plasma CVD, laser CVD, MO-CVD, and thermal CVD, but physical vapor deposition is preferred, and vacuum vapor deposition is particularly preferred. A protective layer (topcoat layer) may be provided on the inorganic barrier layer (Y) as needed, as long as it does not hinder the effects of the present invention. The upper limit of the substrate surface temperature during film formation is preferably 60°C, more preferably 55°C, and even more preferably 50°C. The lower limit of the substrate surface temperature during film formation is not particularly limited, but is preferably 0°C, more preferably 10°C, and even more preferably 20°C. The substrate surface may be plasma-treated before film formation. Known methods can be used for the plasma treatment, and atmospheric pressure plasma treatment is preferred. In atmospheric pressure plasma treatment, nitrogen, helium, neon, argon, krypton, xenon, radon, etc., can be used as the discharge gas. Among these, nitrogen, helium, and argon are preferred, and nitrogen is particularly preferred because it can reduce costs.

[0080] <Multilayer structure> The layer structure of the multilayer structure of the present invention is a multilayer structure having at least a barrier resin layer (X) made of a resin composition (x) containing EVOH (A) and PA (B), and an inorganic barrier layer (Y), wherein at least one pair of barrier resin layers (X) and inorganic barrier layers (Y) must be adjacent to each other. Furthermore, from the viewpoint of improving the appearance and gas barrier properties after retort treatment, it is preferable that at least one barrier resin layer (X) is located on the outer layer side of the inorganic barrier layer (Y).

[0081] <Outer layer and inner layer> The multilayer structure of the present invention preferably has an outer layer and an inner layer mainly composed of polypropylene resin. Since polypropylene resin has excellent heat resistance, mechanical properties, and heat sealability, and is economically available, a multilayer structure having layers mainly composed of polypropylene resin as an outer layer and an inner layer is preferably used as a retort packaging material. The polypropylene resins used for the outer layer and the inner layer may be the same or different. Examples of polypropylene resins include polypropylene; propylene copolymers obtained by copolymerizing propylene with α-olefins such as ethylene, 1-butene, 1-hexene, and 4-methyl-1-pentene. Graft-modified polypropylene obtained by graft-modifying these with acid, and propylene copolymers obtained by copolymerizing propylene with acid can also be exemplified as polypropylene resins. The propylene unit content in the propylene copolymer is preferably 50 mol% or more, more preferably 70 mol% or more, and even more preferably 90 mol% or more. Furthermore, the polypropylene resin content in the outer layer and inner layer is preferably 50% by mass or more, more preferably 70% by mass or more, and even more preferably 90% by mass or more.

[0082] The melting points of the polypropylene resins used for the outer and inner layers are preferably 140°C or higher and less than 170°C, preferably at least one is 150°C or higher and less than 170°C, and more preferably both are 150°C or higher and less than 170°C. When the melting points are within the above range, the heat sealability and retort resistance of the resulting multilayer structure are improved, and furthermore, the uniformity when the multilayer structure is melt-molded after pulverization is excellent. The MFR (melt flow rate, 210°C, under a 2.16 kg load) of the polypropylene resin is typically 0.5 to 50 g / 10 min. When the MFR of the polypropylene is within the above range, the melt-moldability of the pulverized polypropylene resin and the multilayer structure containing the polypropylene resin is improved. In this invention, the MFR of the resin is measured in accordance with JIS K 7210:2014. The density of the polypropylene is typically 0.88 to 0.93 g / cm³. 3 That is the case.

[0083] The outer and inner layers can be films made using the above-mentioned polypropylene resin as the main component. The method for manufacturing these layers is not particularly limited, but is generally done by melt extrusion using an extruder. The outer and inner layers may be unoriented films, uniaxially oriented films, or biaxially oriented films, but from the viewpoint of improving mechanical strength, the outer layer is preferably a biaxially oriented film, and from the viewpoint of improving heat sealability, the inner layer is preferably an unoriented film. The method of stretching is not particularly limited, and both simultaneous stretching and sequential stretching are possible. From the viewpoint of uniformity of the thickness of the resulting film and mechanical strength, the stretching ratio is preferably 8 to 60 times the area ratio. The area ratio is preferably 55 times or less, and more preferably 50 times or less. Furthermore, the stretching ratio is preferably 8 times or more, and more preferably 9 times or more. If the area ratio is less than 8 times, stretching unevenness may remain, and if it exceeds 60 times, the film may easily break during stretching.

[0084] From the viewpoint of industrial productivity, the thickness of the outer and inner layers is preferably 20 to 150 μm. Specifically, for unoriented films, a thickness of 20 to 150 μm is more preferable, and for biaxially oriented films, a thickness of 20 to 60 μm is more preferable.

[0085] The thickness of each layer in the multilayer structure of the present invention may be adjusted as appropriate depending on the application. However, from the viewpoint of suppressing discoloration during melt molding of pulverized material, improving thermal stability during melt molding, and suppressing the generation of lumps, the ratio of the total thickness of the polypropylene resin-based layers to the total thickness of the multilayer structure is preferably 0.75 or higher, and more preferably 0.85 or higher. From the viewpoint of improving gas barrier properties, the ratio is preferably 0.98 or lower.

[0086] Furthermore, the total thickness of the multilayer structure of the present invention is preferably 200 μm or less. Because the total thickness is within this range, the multilayer structure of the present invention is lightweight and flexible, making it suitable for flexible packaging applications. Additionally, the amount of resin used in the multilayer structure is small, thus reducing the environmental impact.

[0087] The multilayer structure of the present invention preferably does not have layers mainly composed of resin with a melting point of less than 140°C, layers mainly composed of resin with a melting point of 240°C or higher, or metal layers with a thickness of 1 μm or more. By not having layers mainly composed of resin with a melting point of less than 140°C, problems such as deformation, whitening, and delamination due to retort processing can be suppressed. On the other hand, by not having layers mainly composed of resin with a melting point of 240°C or higher and metal layers with a thickness of 1 μm or more, it is possible to suppress uneven mixing with other components when melt-molding the pulverized multilayer structure. Here, a metal layer refers to a layer made of metal, such as aluminum foil, that has continuous and discontinuous surfaces.

[0088] The multilayer structure of the present invention exhibits an oxygen permeability rate of 10 cc / (m³) after retort treatment at 125°C for 60 minutes (under conditions of 20°C and 65% RH). 2 It is preferable that it is less than 5cc / (m 2 It is more preferable that it be less than 2cc / (m) day·atm 2 It is particularly preferable that the oxygen permeability rate is less than (day·atm). When the oxygen permeability rate is within the above range, the multilayer structure has excellent gas barrier properties.

[0089] Each layer constituting the multilayer structure of the present invention may be laminated via an adhesive layer, if necessary. The adhesive layer can be formed by applying and drying a known adhesive. A two-component reactive polyurethane adhesive, which involves mixing and reacting a polyisocyanate component and a polyol component, is preferred. The thickness of the adhesive layer is not particularly limited, but is preferably 1 to 5 μm, and more preferably 2 to 4 μm.

[0090] The multilayer structure of the present invention may have other layers besides those described above, as long as they do not impede the effects of the present invention. Examples of other layers include a printed layer. The printed layer may be included at any position in the multilayer structure of the present invention. Examples of the printed layer include a film obtained by coating a solution containing a pigment or dye and, optionally, a binder resin, and drying it. Methods for coating the printed layer include gravure printing, as well as various coating methods using wire bars, spin coaters, die coaters, etc. The thickness of the ink layer is not particularly limited, but is preferably 0.5 to 10 μm, and more preferably 1 to 4 μm.

[0091] It is preferable to reuse the recovered material (scrap) obtained by collecting ends and defective products generated during the manufacturing of the multilayer structure of the present invention. A method for recovering the multilayer structure of the present invention, which involves crushing the multilayer structure and then melt-molding it, and a recovery composition containing the recovered material of the multilayer structure of the present invention are also preferred embodiments of the present invention.

[0092] When recovering the multilayer structure of the present invention, first, the recovered multilayer structure is crushed. The crushed recovered material may be melt-molded as is to obtain a recovered composition, or it may be melt-molded together with other components as needed to obtain a recovered composition. A preferred component to be added to the recovered material is polypropylene resin. The polypropylene resin used in the multilayer structure of the present invention is the one described above. The crushed recovered material may be directly used in the manufacture of molded articles such as multilayer structures, or the crushed recovered material may be melt-molded to obtain pellets made of the recovered composition, and then these pellets may be used in the manufacture of molded articles.

[0093] In the recovered composition, the mass ratio of resin composition (x) to polypropylene resin [resin composition (x) / polypropylene resin] is preferably 1 / 99 to 30 / 70. If the mass ratio is less than 1 / 99, the utilization rate of the recovered material may decrease. On the other hand, if the mass ratio exceeds 30 / 70, the melt moldability and mechanical properties of the recovered composition may decrease.

[0094] The multilayer structure of the present invention is preferable for use as a retort packaging material because it retains excellent gas barrier properties and appearance even after bending treatment following stretching or retort treatment. Furthermore, the multilayer structure of the present invention exhibits excellent uniformity when melt-molded after crushing, and suppresses blemishes and discoloration, thus providing a retort packaging material with high applicability to post-consumer recycling. [Examples]

[0095] The present invention will be described in more detail below using examples.

[0096] (1) Oxygen permeability before retort processing Each example Reference Example Using the multilayer structures obtained in the comparative examples, the oxygen permeation rate was measured with the outer layer on the oxygen supply side and the inner layer on the carrier gas side. Specifically, using an oxygen permeation rate measuring device (MOCON OX-TRAN2 / 21 manufactured by Modern Control Co., Ltd.), the oxygen permeation rate (unit: cc / (m³)) was measured under the following conditions: temperature 40°C, humidity 90%RH on the oxygen supply side, humidity 0%RH on the carrier gas side, oxygen pressure 1 atm, and carrier gas pressure 1 atm. 2 The temperature (day·atm) was measured. Nitrogen gas containing 2 volume% hydrogen gas was used as the carrier gas. The results were evaluated on a 5-point scale from A to E as shown below. Judgment criteria A: 0.1cc / (m 2 Less than (day / atm) B: 0.1cc / (m 2 ·day · atm) or more, 0.25cc / (m 2 Less than (day / atm) C: 0.25cc / (m 2 ·day · atm) or more, 0.5cc / (m 2 Less than (day / atm) D: 0.5cc / (m 2 ·day · atm) or more, 1cc / (m 2 Less than (day / atm) E: 1cc / (m 2 ·day · atm) or more

[0097] (2) Oxygen permeability before retort processing and after stretching processing Each example Reference Example The multilayer structures obtained in the comparative examples were cut to A4 size (with the flow direction being the longitudinal side), then stretched by 5% in the longitudinal direction over 30 seconds, and held in the stretched state for 5 minutes. For the multilayer structures after stretching, the oxygen permeation rate was measured with the outer layer on the oxygen supply side and the inner layer on the carrier gas side. Specifically, the measurement was performed in the same manner as in (1) above, and the results were evaluated using the same criteria.

[0098] (3) Oxygen permeation rate after retort processing Each example Reference Example Two A4-sized sheets of the multilayer structure obtained in the comparative example were cut out, and the inner layers were placed on top of each other so that their inner layers faced each other. A pouch was then fabricated by heat-sealing three sides. Next, 800g of water was filled into the pouch opening, and the opening was heat-sealed to create a water-filled pouch. This was then subjected to retort processing at 125°C for 60 minutes using a retort apparatus (high-temperature, high-pressure cooking and sterilization test machine "RCS-40RTGN" manufactured by Hisaka Works, Ltd.). After retort processing, the water on the surface of the pouch was wiped off, and it was left to stand for 3 hours in a constant temperature and humidity room at 20°C and 65%RH. The pouch was then opened to remove the water, and the oxygen permeation rate was measured with the outer layer as the oxygen supply side and the inner layer as the carrier gas side. Specifically, using an oxygen permeability measuring device (Modern Control's "MOCON OX-TRAN2 / 21"), the oxygen permeation rate (unit: cc / (m³)) was measured under the following conditions: temperature 20°C, humidity 65%RH on the oxygen supply side, humidity 65%RH on the carrier gas side, oxygen pressure 1 atm, and carrier gas pressure 1 atm. 2 The daytime atmospheric pressure (atm) was measured. Nitrogen gas containing 2% by volume of hydrogen gas was used as the carrier gas. The measurement taken 24 hours after the start of measurement was used as the criterion, and the results were evaluated on a five-point scale from A to E as described below. Judgment criteria A: 2cc / (m 2 Less than (day / atm) B: 2cc / (m 2 ·day · atm) or more, 5cc / (m 2 Less than (day / atm) C: 5cc / (m 2·day · atm) or more, 10cc / (m 2 Less than (day / atm) D: 10cc / (m 2 ·day · atm) or more, 20cc / (m 2 Less than (day / atm) E: 20cc / (m 2 ·day · atm) or more

[0099] (4) Oxygen permeability after bending treatment following retort treatment Each example Reference Example The multilayer structures obtained in the comparative examples were subjected to retort treatment in the same manner as in (3) above. After retort treatment, the water on the surface of the pouch was wiped off, and the pouch was left to stand for 3 hours in a constant temperature and humidity room at 23°C and 50%RH. Then the pouch was opened to remove the water, and a bending treatment was performed using a Gelboflex tester (manufactured by Rigaku Kogyo). Specifically, the multilayer structure after retort treatment was first made into a cylindrical shape with a diameter of 3.5 inches, and both ends were grasped. An initial gripping distance of 7 inches, a gripping distance of 1 inch at maximum bending, a twist of 440 degrees at an angle was applied in the first 3.5 inches of the stroke, and then a reciprocating motion consisting of the following motion repeated 10 times at a speed of 40 times / minute for the next 2.5 inches. For the multilayer structure after bending treatment, the oxygen permeation rate was measured with the outer layer on the oxygen supply side and the inner layer on the carrier gas side. Specifically, the measurement was performed in the same manner as in (3) above, and the results were evaluated using the same criteria.

[0100] (5) Appearance after retort processing Each example Reference Example The multilayer structures obtained in the comparative examples were subjected to retort treatment in the same manner as in (3) above. After retort treatment, the water on the surface of the pouch was wiped off, and the pouch was left to stand for 3 hours in a room with constant temperature and humidity of 20°C and 65%RH. The appearance characteristics of the pouch were then evaluated on a four-point scale from A to D as described below. Judgment criteria A: There was almost no change in appearance compared to before retort processing. B: Mild whitening, discoloration, and deformation were observed. C: Moderate whitening, discoloration, deformation, or partial delamination is observed. D: Severe whitening, deformation, or widespread delamination is observed.

[0101] (6) Light transmittance before and after retort processing Each example Reference Example The light transmittance at a wavelength of 600 nm was measured for the multilayer structures obtained in the comparative examples using a Shimadzu UV-2450 ultraviolet-visible spectrophotometer. Subsequently, retort treatment was performed in the same manner as in (3) above. After retort treatment, the water on the surface of the pouch was wiped off and left to stand for 3 hours in a room with constant temperature and humidity of 20°C and 65%RH. The light transmittance of the multilayer structures obtained after retort treatment in the same manner was measured. The measurement results were evaluated in four stages from A to D below. Standards A and B can be preferably used in applications where transparency and visibility of contents are required. Standard D can be preferably used in applications where light shielding is required. Judgment criteria A: Light transmittance of 90% or more at 600nm B: Light transmittance at 600nm is 80% or more, but less than 90%. C: Light transmittance at 600nm is 10% or more and less than 80%. D: Light transmittance at 600nm is less than 10%

[0102] (7) Bumps and discoloration in molten molded products of crushed multilayer structures Each example Reference Example The multilayer structures obtained in the comparative examples were crushed to a size of 4 mm square or less. This crushed material was blended with polypropylene resin (Novatec PP EA7AD, manufactured by Nippon Polypropylene Co., Ltd., density 0.90 g / cc, MFR (230°C, under 2.16 kg load) 1.4 g / 10 min) in a mass ratio (crushed material / polypropylene resin) of 40 / 60, and a single-layer film was produced under the extrusion conditions shown below to obtain a single-layer film with a thickness of 50 μm. The thickness of the single-layer film was adjusted by appropriately changing the screw rotation speed and take-up roll speed. As a control, a single-layer film with a thickness of 50 μm was similarly obtained using only polypropylene resin. Extruder: Single-screw extruder manufactured by Toyo Seiki Seisakusho Co., Ltd. Screw diameter: 20mmφ (L / D=20, Compression ratio=3.5, Full flight type) Extrusion temperature: Feed unit / Compression unit / Measuring unit / Die = 230 / 230 / 230 / 230℃ Take-up roll temperature: 80℃ The resulting single-layer films were evaluated for their material properties and coloration on a four-point scale from A to D. Criteria for judging the product A: The amount of substance remained almost unchanged compared to the control group. B: Compared to the control, there was a slightly larger amount of small particles. C: Compared to the control, there was a greater quantity of small particles. D: There was a greater quantity of large pieces compared to the control group. Criteria for determining discoloration A: The degree of hue change was smaller compared to the control. B: Mild discoloration was observed compared to the control. C: Moderate discoloration was observed compared to the control group. D: Compared to the control group, significant discoloration was observed, and unevenness was also seen.

[0103] (8) Melt viscosity stability of pulverized multilayer structures Each example Reference Example The multilayer structures obtained in the comparative examples were pulverized to a size of 4 mm square or less. 60 g of this pulverized material was kneaded using a Laboplast mill (two-axis anomalous direction) under a nitrogen atmosphere at 230°C and 100 rpm, and the torque change was measured. Torque values ​​(TI and TF, respectively) were calculated 10 minutes and 90 minutes after the start of kneading, and the ratio of these values ​​(TF / TI) was evaluated in four stages, A to D, as described below. Judgment criteria A: 80 / 100 or more, less than 120 / 100 B: 60 / 100 or more but less than 80 / 100, or 120 / 100 or more but less than 140 / 100 C: 40 / 100 or more but less than 60 / 100, or 140 / 100 or more but less than 160 / 100 D: Less than 40 / 100, or 160 / 100 or more.

[0104] [Examples of resin composition production] (1) Synthesis of EVAc In a 250L pressurized reactor equipped with a jacket, stirrer, nitrogen inlet, ethylene inlet, and initiator addition port, 100 kg of vinyl acetate, 10 kg of methanol, and 2.9 kg of 2-methylene-1,3-propanediol diacetate (hereinafter referred to as MPDAc) were charged. After raising the temperature to 60°C, the reactor was purged with nitrogen by bubbling with nitrogen for 30 minutes. Next, ethylene was introduced so that the reactor pressure (ethylene pressure) reached 4.9 MPa. After adjusting the temperature in the reactor to 60°C, 36 g of 2,2'-azobis(2,4-dimethylvaleronitrile) (manufactured by Wako Pure Chemical Industries, Ltd., "V-65") was added as a methanol solution as an initiator, and polymerization was started. During polymerization, the ethylene pressure was maintained at 4.9 MPa and the polymerization temperature at 60°C. After 6 hours, when the polymerization rate of vinyl acetate reached 45%, the reactor was cooled and polymerization was stopped. After opening the reaction vessel and removing the ethylene, nitrogen gas was bubbled in to completely remove the ethylene. Then, after removing the unreacted vinyl acetate under reduced pressure, methanol was added to the modified ethylene-vinyl acetate copolymer (hereinafter sometimes referred to as modified EVAc), in which structural units derived from MPDAc were introduced by copolymerization, to obtain a 20% by mass methanol solution.

[0105] (2) Saponification of EVAc A 20% by mass methanol solution of the modified EVAc obtained in (1) was charged into a 500L reaction vessel equipped with a jacket, stirrer, nitrogen inlet, reflux condenser, and solution addition port. The temperature of this solution was raised to 60°C while blowing nitrogen into it, and 0.5 equivalents of sodium hydroxide in a 2 N methanol solution were added to the vinyl acetate units in the modified EVAc. After the addition of the sodium hydroxide methanol solution was completed, the saponification reaction was carried out by stirring for 2 hours while maintaining the temperature in the system at 60°C. Then, acetic acid was added to stop the saponification reaction. Next, while heating and stirring at 60-80°C, deionized water was added, and methanol was distilled out of the reaction vessel to precipitate modified EVOH. The precipitated modified EVOH was collected and pulverized in a mixer. The obtained modified EVOH powder was added to a 1 g / L aqueous acetic acid solution (bath ratio 20: 20 L of aqueous solution per 1 kg of powder) and stirred and washed for 2 hours. This was dehydrated and added again to a 1 g / L aqueous acetic acid solution (bath ratio 20) and stirred and washed for 2 hours. The dehydrated product was placed in deionized water (bath ratio 20), stirred and washed for 2 hours, and the dehydrated product was repeated three times to purify it. Next, it was immersed in 10 L of aqueous solution containing 0.5 g / L acetic acid and 0.1 g / L sodium acetate with stirring for 4 hours, then dehydrated, and dried at 60°C for 16 hours to obtain a crude dried product of modified EVOH.

[0106] (3) Production of water-containing pellets of modified EVOH In an 80L stirring tank equipped with a jacket, stirrer, and reflux condenser, the crudely dried modified EVOH obtained in (2), water, and methanol were charged and heated to 80°C to dissolve. This solution was extruded through a 4mm diameter tube into a water / methanol mixture of 90 / 10 cooled to 5°C to precipitate in strands, and these strands were cut into pellets with a strand cutter to obtain hydrated pellets of modified EVOH. The moisture content of the obtained hydrated pellets of modified EVOH was measured using a Mettler halogen moisture meter "HR73" and was found to be 60% by mass.

[0107] (4) Production of modified EVOH composition pellets The hydrated pellets of modified EVOH obtained in (3) above were placed in a 1 g / L aqueous acetic acid solution (bath ratio 20) and stirred and washed for 2 hours. After dewatering, the pellets were placed again in a 1 g / L aqueous acetic acid solution (bath ratio 20) and stirred and washed for 2 hours. After dewatering, the aqueous acetic acid solution was replaced and the same procedure was repeated. The pellets washed in aqueous acetic acid solution and then dewatered were placed in ion-exchanged water (bath ratio 20) and stirred and washed for 2 hours, and dewatered. This process was repeated three times to purify the pellets and obtain hydrated pellets of modified EVOH from which the catalyst residue from the saponification reaction had been removed. These hydrated pellets were placed in an aqueous solution of sodium acetate (concentration 0.5 g / L), acetic acid (concentration 0.8 g / L), and phosphoric acid (concentration 0.005 g / L) (bath ratio 20) and immersed for 4 hours with periodic stirring. After dewatering, the pellets were dried at 80°C for 3 hours and at 105°C for 16 hours to obtain modified EVOH composition pellets.

[0108] (5) Content of each structural unit and degree of saponification of modified EVOH Modified EVAc and modified EVOH after saponification were prepared according to the method described in WO2014 / 024912A1. 1 ¹H-NMR measurements were performed to determine the content of each structural unit of denatured EVOH [the content of a, b, and c in formula (I)] and the degree of saponification. The results are shown in Table 1.

[0109] (6) MFR of EVOH The modified EVOH composition pellets obtained in (4) above were subjected to a measurement of the MFR at a temperature of 210°C and a load of 2160 g in accordance with JIS K7210 (1999). The MFR was 4.0 g / 10 min. (Note: The examples in this specification...) Reference Example The MFRs of the EVOH compositions used in the comparative examples were all within the range of 3.5 to 4.5 g / 10 min.

[0110] (7) Sodium salt content and phosphate compound content in the EVOH composition 0.5 g of the modified EVOH composition pellet obtained in (4) above was placed in a Teflon® pressure vessel, and 5 mL of concentrated nitric acid was added to decompose it at room temperature for 30 minutes. After 30 minutes, the lid was closed, and decomposition was carried out by heating at 150°C for 10 minutes, then at 180°C for 5 minutes, using a wet decomposition apparatus (Actac Co., Ltd.: "MWS-2"), and then cooled to room temperature. This processed solution was transferred to a 50 mL volumetric flask (TPX) and diluted with pure water. The metal content of this solution was analyzed using an ICP emission spectrometer (PerkinElmer "OPTIMA4300DV") to determine the sodium salt content and phosphate compound content in the modified EVOH composition pellet. The sodium salt content was 150 ppm in terms of sodium element, and the phosphate compound content was 10 ppm in terms of phosphate root. Note: Examples in this specification Reference Example The sodium salt content and phosphate compound content in the EVOH compositions used in the comparative examples were both within the ranges of 140-160 ppm and 5-15 ppm, respectively.

[0111] (8) Manufacturing of resin compositions 85 parts by weight of the modified EVOH composition pellets obtained in (4) above, 15 parts by weight of Ube Industries nylon 6 "SF1018A" pellets (hereinafter abbreviated as "PA6": relative viscosity [ηr] 3.0, melting point 221℃), and magnesium hydroxide powder (120 ppm in terms of magnesium ions) were mixed and then supplied to a Japan Steel Works Ltd. twin-screw extruder "TEX30α" (screw diameter 30 mm). Using a screw with a forward-shifted kneading disc L (screw length) / D (screw diameter) = 3, melt extrusion was performed at a melting temperature of 230-240℃ and an extrusion speed of 20 kg / hr to obtain strands. After cooling and solidifying the obtained strands in a cooling tank, they were cut to obtain resin composition pellets.

[0112] refer to Example 1 [Film formation of single-layer films] Using the resin composition pellets obtained above, single-layer films were produced under the extrusion conditions shown below to obtain single-layer films with thicknesses of 15 μm and 30 μm. The thickness of the single-layer films was adjusted by appropriately changing the screw rotation speed and the take-up roll speed. Extruder: Single-screw extruder manufactured by Toyo Seiki Seisakusho Co., Ltd. Screw diameter: 20mmφ (L / D=20, Compression ratio=3.5, Full flight type) Extrusion temperature: Feed unit / Compression unit / Measuring unit / Die = 230 / 230 / 230 / 230℃ Take-up roll temperature: 80℃

[0113] A 30 nm thick alumina deposition layer was carried out on one side of the obtained single-layer film using a known vacuum deposition method. Next, a two-component adhesive (Mitsui Chemicals, "Takelac A-520" and "Takenate A-50") was coated onto one side of each of a biaxially oriented polypropylene film (Toyobo Co., Ltd., "Pyrene Film-OT P2161", 30 μm thick) and an unoriented polypropylene film (Mitsui Chemicals, Tohcello Co., Ltd., "RXC-22", 50 μm thick) to a dry thickness of 2 μm and then dried. Hereinafter, the alumina deposition layer may be abbreviated as AlOx, the biaxially oriented polypropylene film as BOPP, the unoriented polypropylene film as CPP, and the adhesive layer as Ad.

[0114] Next, BOPP and CPP coated with adhesive were laminated with the alumina-deposited single-layer film to obtain a multilayer structure having the structure (outer layer) BOPP30 / Ad2 / resin composition 15 / AlOx / Ad2 / CPP50 (inner layer). The numbers in the symbols representing each layer represent the thickness (μm) of each layer. Here, the alumina-deposited single-layer film was arranged so that the alumina-deposited layer was on the CPP side and the resin composition layer was on the BOPP side. Various evaluations (1) to (8) above were performed using this multilayer structure. The results are shown in Table 3.

[0115] refer to Examples 2-22, 26-28, and Comparative Examples 1-6 Aside from the changes made to the composition of the resin composition and the layer structure of the multilayer structure as shown in Table 2, refer toA multilayer structure was obtained in the same manner as in Example 1. refer to In Examples 2 and 7, instead of modified EVOH, EVOH with an ethylene content of 38 mol% and a degree of saponification of 99.95 mol% was used, and other refer to Modified EVOH in the examples and comparative examples was produced by changing the polymerization conditions. Furthermore, when polyvalent metal ions were added as acetates, they were supplied to the twin-screw extruder as an aqueous solution, and a vacuum vent was installed downstream of the supply section to remove volatile components. The resulting multilayer structure was then prepared. refer to The evaluation was performed using the same method as in Example 1. The evaluation results are shown in Table 3. Here, the layers used in the multilayer structure described in Table 2 are as follows. BOPP30: Biaxially oriented polypropylene film (Toyobo Co., Ltd. "Pyrene Film-OT P2161", melting point 164℃, thickness 30μm) CPP50: Unoriented polypropylene film (Tohsero Corporation "RXC-22", melting point 166℃, thickness 50μm) BOPET12: Stretched polyethylene terephthalate film (Toray Industries, Ltd. "Lumirror P60", melting point 256℃, thickness 12μm) PE50: Unoriented polyethylene film (TUX HZR-2 manufactured by Tosello Co., Ltd., melting point 127℃, thickness 50μm) VM: A metal vapor-deposited layer of aluminum formed by a known vacuum deposition method. AlOx: Inorganic oxide deposition layer of alumina deposited by a known vacuum deposition method. SiOx: An inorganic oxide deposition layer of silica deposited by a known vacuum deposition method. In Table 2, the permutation of the vapor-deposited layer and the layer to be vapor-deposited is taken into consideration, and is expressed as, for example, "AlOx / resin composition" or "resin composition / AlOx". For example, refer to In the multilayer structure of Example 1, the AlOx layer is laminated on the inner layer side, and the resin composition layer is laminated on the outer layer side. This notation is the same for other vapor-deposited layers. Also, in Table 2, for multilayer structures including co-extruded films, the portion composed of the co-extruded film is indicated in parentheses, for example, (PP90 / resin composition 9). Note that "BO" means that it is a biaxially oriented film.

[0116] Example 23 [Film formation of biaxially oriented single-layer films] Except for changing the screw rotation speed and the take-up roll speed. refer to A single-layer film with a thickness of 135 μm was obtained in the same manner as in Example 1. The moisture content of this single-layer film was adjusted to 15%, and it was stretched three times in the longitudinal direction and three times in the transverse direction at 80°C using a tenter-type simultaneous biaxial stretching machine to obtain a biaxially oriented single-layer film with a thickness of 15 μm. Except for using the obtained biaxially oriented single-layer film in place of the single-layer film, refer to A multilayer structure was obtained in the same manner as in Example 1. Various evaluations were performed on the obtained multilayer structure. The results are shown in Table 3.

[0117] Example 24 [Film formation of co-extruded films] refer to Using the resin composition pellets obtained in Example 1, polypropylene resin (Novatec PP EA7AD manufactured by Nippon Polypropylene Co., Ltd. (density 0.90 g / cc, MFR (230°C, under 2.16 kg load) 1.4 g / 10 min)), and polypropylene adhesive resin (Admer QF500 manufactured by Mitsui Chemicals, Inc. (MFR (230°C, under 2.16 kg load) 3.0 g / 10 min)), a three-layer co-extruded film (resin composition / polypropylene adhesive resin / polypropylene resin = 9 μm / 9 μm / 81 μm) was fabricated. The thickness of the co-extruded film was adjusted by appropriately changing the screw rotation speed and take-up roll speed. The extruder, extrusion conditions, and die used were as follows. resin composition Extruder: Single-screw extruder (Toyo Seiki Co., Ltd. Lab machine ME type CO-EXT) Screw: 20mm diameter, L / D20, full-flight screw Extrusion temperature: Feed unit / Compression unit / Measuring unit / Die = 230 / 230 / 230 / 230℃ Polypropylene adhesive resin Extruder: Single-screw extruder (Technovel Corporation SZW20GT-20MG-STD) Screw: 20mm diameter, L / D20, full-flight screw Extrusion temperature: Feed unit / Compression unit / Measuring unit / Die = 150 / 200 / 220 / 230℃ Polypropylene resin Extruder: Single-screw extruder (Plastics Engineering Laboratory Co., Ltd. GT-32-A) Screw: 32mm diameter, L / D 28, full-flight screw Extrusion temperature: Feeding section / Compression section / Measuring section / Die = 170 / 220 / 230 / 230℃ Die: 300mm wide, 3 types, 3-layer coat hanger die (manufactured by Plastics Engineering Laboratory Co., Ltd.) Die temperature: 230℃ Except for using the resulting co-extruded film in place of the single-layer film, refer to A multilayer structure was obtained in the same manner as in Example 1. Various evaluations were performed on the obtained multilayer structure. The results are shown in Table 3. In Table 2, the polypropylene adhesive resin and polypropylene resin that constitute the co-extruded film are collectively referred to as "PP".

[0118] Example 25 [Film formation of biaxially oriented co-extruded films] Except for changing the screw rotation speed and the take-up roll speed, a three-layer co-extruded film (resin composition / polypropylene adhesive resin / polypropylene resin = 27 μm / 27 μm / 243 μm) was produced in the same manner as in Example 24. This co-extruded film was stretched three times in the longitudinal direction and then three times in the transverse direction at 150°C using a tenter-type sequential biaxial stretching equipment to obtain a three-layer biaxially oriented co-extruded film (resin composition / polypropylene adhesive resin / polypropylene resin = 3 μm / 3 μm / 27 μm). Except for using the resulting biaxially oriented co-extruded film in place of a single-layer film, refer to A multilayer structure was obtained in the same manner as in Example 1. Various evaluations were performed on the obtained multilayer structure. The results are shown in Table 3.

[0119] Comparative Example 7 A 30 nm thick layer of alumina was deposited onto one side of the biaxially oriented polypropylene film BOPP30 using a known vacuum deposition method. Next, a two-component adhesive (Mitsui Chemicals' "Takelac A-520" and "Takenate A-50") was coated onto one side of an unoriented polypropylene film (Tohsero "RXC-22", 50 μm thick) to a dry thickness of 2 μm and then dried. Subsequently, the adhesive-coated CPP and the alumina-deposited OPP film were laminated to obtain a multilayer structure having the structure (outer layer) OPP30 / AlOx / Ad2 / CPP50 (inner layer). Various evaluations were performed on the obtained multilayer structure. The results are shown in Table 3.

[0120] Comparative Example 8 Except for not depositing alumina onto the biaxially oriented polypropylene film BOPP30, the procedure was the same as in Comparative Example 7. A CPP film coated with adhesive and an OPP film were laminated to obtain a multilayer structure having the structure (outer layer) OPP30 / Ad2 / CPP50 (inner layer). Various evaluations were performed on the obtained multilayer structure. The results are shown in Table 3.

[0121] [Table 1]

[0122] [Table 2]

[0123] [Table 3]

Claims

1. A multilayer structure comprising at least a barrier resin layer (X) and an inorganic barrier layer (Y) which is an inorganic oxide vapor-deposited layer (Y2) with a thickness of 90 nm or less, wherein at least one pair of barrier resin layers (X) and inorganic barrier layers (Y) are adjacent to each other, and at least one barrier resin layer (X) is located on the outer layer side of the inorganic barrier layer (Y), The multilayer structure has an outer layer and an inner layer, and the polypropylene resin content in the outer layer and the inner layer is 50% by mass or more, The layer (X) consists of a resin composition (x) containing an ethylene-vinyl alcohol copolymer (A) and a polyamide (B) in a mass ratio (A / B) of 55 / 45 to 93 / 7. The resin composition (x) contains 20 to 400 ppm of at least one polyvalent metal ion (C) selected from the group consisting of magnesium ions, calcium ions, and zinc ions. A multilayer structure in which the ethylene-vinyl alcohol copolymer (A) has an ethylene content of 30-40 mol% and a degree of saponification of 90 mol% or more, and the layer (X) is a biaxially oriented single-layer film.

2. A multilayer structure comprising at least a barrier resin layer (X) and an inorganic barrier layer (Y) which is an inorganic oxide vapor-deposited layer (Y2) with a thickness of 90 nm or less, wherein at least one pair of barrier resin layers (X) and inorganic barrier layers (Y) are adjacent to each other, and at least one barrier resin layer (X) is located on the outer layer side of the inorganic barrier layer (Y), The multilayer structure has an outer layer and an inner layer, and the polypropylene resin content in the outer layer and the inner layer is 50% by mass or more, The layer (X) consists of a resin composition (x) containing an ethylene-vinyl alcohol copolymer (A) and a polyamide (B) in a mass ratio (A / B) of 55 / 45 to 93 / 7. The resin composition (x) contains 20 to 400 ppm of at least one polyvalent metal ion (C) selected from the group consisting of magnesium ions, calcium ions, and zinc ions. A multilayer structure in which the ethylene-vinyl alcohol copolymer (A) has an ethylene content of 30 to 40 mol% and a degree of saponification of 90 mol% or more, and layer (X) is one layer of a co-extruded film consisting of two or more layers including layer (X).

3. The multilayer structure according to claim 1 or 2, wherein the ethylene-vinyl alcohol copolymer (A) is a modified ethylene-vinyl alcohol copolymer (A2) represented by the following formula (I), the content (mol%) of a, b, and c relative to the total monomer units satisfies the following formulas (1) to (3), and the degree of saponification defined by the following formula (4) is 90 mol% or more. 【Chemistry 1】 [In formula (I), R １ , R ２ , R ３ and R ４ Each of these independently represents a hydrogen atom or an alkyl group having 1 to 10 carbon atoms, and the alkyl group may contain a hydroxyl group, an alkoxy group, or a halogen atom. Each of X, Y, and Z independently represents a hydrogen atom, a formyl group, or an alkanoyl group having 2 to 10 carbon atoms. 20 ≤ a ≤ 46 (1) 0.3 ≤ c ≤ 10 (2) [100-(a+c)]×0.9≦b≦[100-(a+c)] (3) Degree of saponification = [(Total number of moles of hydrogen atoms among X, Y, and Z) / (Total number of moles of X, Y, and Z)] × 100 (4)

4. The multilayer structure according to claim 1, wherein the barrier resin layer (X) has a thickness of 8 to 20 μm.

5. The multilayer structure according to claim 2, wherein the thickness of the co-extruded film is 8 to 120 μm, and the thickness of the barrier resin layer (X) is 0.5 to 20 μm.

6. The multilayer structure according to claim 2, wherein a co-extruded film is biaxially stretched.

7. The multilayer structure according to claim 5 or 6, wherein the layers other than the barrier resin layer (X) of the co-extruded film consist of layers containing only polypropylene resin.

8. A multilayer structure according to any one of claims 1 to 7, which does not have a layer mainly composed of a resin with a melting point of less than 140°C, a layer mainly composed of a resin with a melting point of 240°C or higher, or a metal layer with a thickness of 1 μm or more.

9. A multilayer structure according to any one of claims 1 to 8, wherein the ratio of the total thickness of the polypropylene resin layer to the total thickness of the multilayer structure is 0.75 or more.

10. A retort packaging material having a multilayer structure according to any one of claims 1 to 9.

11. The oxygen permeation rate after retort treatment at 125°C for 60 minutes (under 20°C and 65% RH conditions) was 10 cc / (m³). ２ The retort packaging material according to claim 10, wherein the temperature is less than ・day・atm.

12. The retort packaging material according to claim 10 or 11, wherein the light transmittance at a wavelength of 600 nm after retort treatment at 125°C for 60 minutes is 80% or more.

13. A recovery composition comprising a recovered multilayer structure according to any one of claims 1 to 9.

14. A method for recovering a multilayer structure, comprising crushing the multilayer structure according to any one of claims 1 to 9 and then melt-molding it.

15. A method for manufacturing a multilayer structure according to any one of claims 1 to 9, A method for producing a multilayer structure in which polyvalent metal ions (C) are incorporated into the resin composition (x) either in a solid state or as a molten material.

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