Multilayer film and multilayer structure using the same

Abstract

To provide a multilayer film that comprises an EVOH layer as the outermost layer and is drawn at least in an uniaxial direction, where the multilayer film has reduced curling properties while maintaining good gas barrier properties.SOLUTION: A multilayer film comprises a barrier layer (A), an adhesive layer (B), and a moisture-proof layer (C) laminated in this order, where at least one barrier layer (A) is positioned as the outermost layer of the multilayer film, the barrier layer (A) comprises, as the main component, EVOH (a) having an ethylene unit content of 20 mol% to 50 mol% and a saponification degree of 90 mol% or more, the adhesive layer (B) comprises, as the main component, an adhesive resin (b) having a melting point of less than 150°C, the moisture-proof layer (C) comprises, as the main component, a polyolefin resin (c) having a melting point of less than 150°C, the multilayer film is drawn at least in an uniaxial direction by 3 times or more, and a wound diameter, when a sample of 10 cm square is cut out from an arbitrary position of the multilayer film and allowed to stand still under an atmosphere of 20°C and 65% RH for 24 hours, is 14 mm or more.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a multilayer film which has a resin composition layer containing an ethylene-vinyl alcohol copolymer as an outermost layer and is stretched at least in one direction, a method for producing the same, a vapor-deposited multilayer film using the multilayer film, a multilayer structure using the multilayer film or the vapor-deposited multilayer film, and a packaging material including the multilayer structure. [Background technology]

[0002] Ethylene-vinyl alcohol copolymer (hereinafter sometimes abbreviated as "EVOH") has excellent transparency, gas barrier properties, aroma retention, solvent resistance, oil resistance, etc., and taking advantage of these properties, it is used in a wide range of applications, such as various types of packaging for food, medicines, industrial chemicals, and pesticides, as well as industrial and agricultural films, floor heating pipes, and fuel containers.

[0003] In recent years, environmental and waste problems have led to a worldwide increase in the demand for post-consumer recycling (hereinafter sometimes simply referred to as "recycling"), which involves recovering and recycling packaging materials consumed in the market, and packaging materials with excellent recyclability are desired. For example, attempts have been made to produce packaging films based only on polyethylene or polypropylene, which have low gas barrier properties, and packaging films with excellent gas barrier properties that are mixed or laminated with low amounts of gas barrier materials that can be mixed with polyethylene or polypropylene, and have excellent recyclability.

[0004] Patent Document 1 describes that by providing an EVOH layer of a specific thickness on the outermost layer of a laminate, the heat sealing speed can be increased without impairing recyclability when used as a packaging film, and also describes that by stretching the laminate in one axial direction, the laminate becomes excellent in transparency and gas barrier properties.

[0005] Furthermore, Patent Document 2 describes a multilayer film having an EVOH layer as the outermost layer, in which at least two types of EVOH having different ethylene unit contents are mixed as the EVOH, thereby suppressing blocking between the EVOH layers even during stretching after inflation molding. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] International Publication No. 2019 / 243456 [Patent Document 2] International Publication No. 2021 / 210606 Summary of the Invention [Problem to be solved by the invention]

[0007] However, in the laminates described in Patent Documents 1 and 2 having an EVOH layer on the outermost layer and stretched in at least one direction, wrinkles may occur during converting such as printing or lamination. Although the occurrence of wrinkles during converting can be suppressed by having a polyolefin layer on the outermost layer, the gas barrier property becomes insufficient in that case, and even a vapor deposition laminate having an inorganic vapor deposition layer on the polyolefin layer will have insufficient gas barrier property after bending, so a configuration having an EVOH layer on the outermost layer is essential.

[0008] The present invention has been made to solve the above-mentioned problems, and its object is to provide a multilayer film having an EVOH outermost layer and stretched at least uniaxially, which maintains good gas barrier properties before and after a bending test while suppressing the occurrence of wrinkles after converting, a method for producing the same, a vapor-deposited multilayer film using the multilayer film, a multilayer structure using the multilayer film or the vapor-deposited multilayer film, and a packaging material including the multilayer structure. In this specification, the property of being able to suppress the occurrence of wrinkles after converting may be referred to as "converting suitability". [Means for solving the problem]

[0009] According to the present invention, the above object is to [1] A multilayer film having a structure in which a barrier layer (A), an adhesive layer (B) and a moisture-proof layer (C) are laminated in this order, at least one barrier layer (A) is located as the outermost layer of the multilayer film, the barrier layer (A) contains as a main component an ethylene-vinyl alcohol copolymer (a) having an ethylene unit content of 20 mol% to 50 mol% and a saponification degree of 90 mol% or more, the adhesive layer (B) contains as a main component an adhesive resin (b) having a melting point of less than 150°C, and the moisture-proof layer (C) contains as a main component a polyolefin resin (c) having a melting point of less than 150°C, the multilayer film is stretched at least 3 times in one axial direction, and a 10 cm square cut from any position of the multilayer film and left to stand in an atmosphere of 20°C and 65% RH for 24 hours has a roll diameter of 14 mm or more; [2] The multilayer film of [1], wherein the ethylene unit content of the ethylene-vinyl alcohol copolymer (a) is less than 34 mol%; [3] The multilayer film of [1], wherein the ethylene-vinyl alcohol copolymer (a) comprises an ethylene-vinyl alcohol copolymer (a1) having an ethylene unit content of 22 mol% or more and less than 34 mol% and a degree of saponification of 99 mol% or more, and an ethylene-vinyl alcohol copolymer (a2) having an ethylene unit content of 34 mol% or more and less than 50 mol% and a degree of saponification of 99 mol% or more, and the mass ratio (a1 / a2) of the ethylene-vinyl alcohol copolymer (a1) to the ethylene-vinyl alcohol copolymer (a2) is 80 / 20 to 98 / 2; [4] The multilayer film of any of [1] to [3], wherein the barrier layer (A) contains 10 to 300 ppm of at least one polyvalent metal ion (d) selected from the group consisting of magnesium ions, calcium ions, and zinc ions; [5] The multilayer film of any of [1] to [4], wherein the barrier layer (A) contains 100 to 4000 ppm of a higher aliphatic carboxylic acid (e) having 8 to 30 carbon atoms; [6] The multilayer film of any one of [1] to [5], wherein the polyolefin resin (c) contains a polyethylene resin as a main component; [7] Any of the multilayer films of [1] to [6], in which the thickness of the barrier layer (A) is 0.2 μm or more and less than 10 μm, and the ratio of the thickness of the barrier layer (A) to the total thickness of all layers of the multilayer film is less than 20%; [8] The multilayer film of any one of [1] to [7], which is stretched at least three times in the machine direction and is not substantially stretched in the width direction; [9] The multilayer film of any one of [1] to [8], wherein the multilayer film is an inflation-molded product;

[10] A vapor-deposited multilayer film comprising an inorganic vapor-deposited layer (I) on the exposed surface side of the barrier layer (A) in the multilayer film according to any one of [1] to [9];

[11] The oxygen transmission rate measured according to JIS K 7126-2 (isobaric method; 2006) under conditions of 20°C and 65% RH is 30cc / (m 2 any one of the multilayer films or vapor-deposited multilayer films of [1] to

[10] , wherein the thermal expansion coefficient is less than 1.0·day·atm;

[12] A multilayer structure comprising a multilayer film or a vapor-deposited multilayer film according to any one of [1] to

[11] and a resin layer (R) containing a thermoplastic resin (r) as a main component;

[13] The multilayer structure of

[12] , wherein the thermoplastic resin (r) contains, as a main component, a polyolefin resin having a melting point of less than 150°C;

[14] The multilayer structure of any of

[12] or

[13] , wherein the thermoplastic resin (r) comprises a polyethylene resin as a main component;

[15] The multilayer structure of any one of

[12] to

[14] , wherein at least one of the moisture proof layer (C) and the resin layer (R) contains polyethylene resin as a main component, and the ratio of the total thickness of the layer containing polyethylene resin as a main component to the total thickness of the multilayer structure is 0.75 or more;

[16] The multilayer structure of any of

[12] to

[15] , which does not have a layer containing, as a main component, a resin having a melting point of 240°C or more and a metal layer with a thickness of 1 μm or more;

[17] A packaging material having the multilayer structure according to any one of

[12] to

[16] ;

[18] A method for producing a multilayer film according to any one of [1] to [9], comprising: a step (I) of producing an unstretched multilayer film having a barrier layer (A), an adhesive layer (B) and a moisture-proof layer (C) in this order; a step (II) of stretching the obtained unstretched multilayer film at least in one axial direction to produce a pre-treated multilayer film; and a step (III) of treating the pre-treated multilayer film after stretching under conditions of a temperature of 28°C or higher and 60°C or lower and a humidity of 65% RH or higher; This is achieved by providing: Effect of the Invention

[0010] According to the present invention, there are provided a multilayer film which has an EVOH layer as an outermost layer and is stretched at least in one direction, in which the occurrence of wrinkles after converting is suppressed while maintaining good gas barrier properties before and after a bending test, a method for producing the multilayer film, a vapor-deposited multilayer film using the multilayer film, a multilayer structure using the multilayer film or the vapor-deposited multilayer film, and a packaging material including the multilayer structure. [Brief description of the drawings]

[0011] [Figure 1] FIG. 2 is a schematic diagram for explaining how to consider the winding diameter when a multilayer film does not become cylindrical but curls in a diagonal direction. [Diagram 2] FIG. 2 is a schematic diagram for explaining the concept of the winding diameter when the multilayer film curls in the MD or TD direction without becoming cylindrical. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] The multilayer film of the present invention comprises a barrier layer (A), an adhesive layer (B) and a moisture-proof layer (C) laminated in this order, at least one barrier layer (A) being located as the outermost layer, the barrier layer (A) comprising, as a main component, an ethylene-vinyl alcohol copolymer (a) (hereinafter may be abbreviated as "EVOH (a)") having an ethylene unit content of 20 mol% or more and 50 mol% or less and a degree of saponification of 90 mol% or more, the adhesive layer (B) comprising, as a main component, an adhesive resin (b) (hereinafter may be simply referred to as "adhesive resin (b)") having a melting point of less than 150°C, and the moisture-proof layer (C) comprising, as a main component, a polyolefin resin (c) (hereinafter may be abbreviated as "PO (c)") having a melting point of less than 150°C, the multilayer film being stretched at least 3 times in one axial direction, and a 10 cm square cut from any position of the multilayer film and left to stand in an atmosphere of 20°C and 65% RH for 24 hours has a roll diameter of 14 mm or more.

[0013] In this specification, the phrase "a barrier layer (A), an adhesive layer (B), and a moisture-proof layer (C) laminated in this order" is not particularly limited as long as the layer structure has a barrier layer (A), an adhesive layer (B), and a moisture-proof layer (C) laminated in this order, and does not, for example, preclude the inclusion of other layers between each layer. "Major component" means a component that is contained in an amount of more than 50% by mass. "ppm" means the content by mass (ppm by mass). "Polyethylene" refers to a homopolymer of ethylene, a copolymer of 80 mol% or more ethylene and 20 mol% or less α-olefin monomer, and a copolymer of 90 mol% or more ethylene and less than 10 mol% of a non-olefin monomer whose functional group does not contain atoms other than carbon atoms, oxygen atoms, and hydrogen atoms. In addition, the "surface (or surface layer)" of a multilayer structure does not mean a distinction between the front and back, but refers to the exposed surface. In other words, a multilayer structure has two surfaces. Similarly, a multilayer structure has two outermost layers.

[0014] The multilayer film of the present invention has insufficient suitability for converting if the roll diameter is less than 14 mm when cut from an arbitrary position in a 10 cm square and left to stand for 24 hours in an atmosphere of 20°C and 65% RH. Here, the "roll diameter" means the diameter of a circle when the multilayer film is cylindrical. When the film is not cylindrical and both ends are curled, for example, taking FIG. 1 or FIG. 2 as an example, it means the longest distance in the curl direction (the distance between A and B, and the distance between A' and B') between the end (A or A') of one side (the side connecting A and A') perpendicular to the curl direction when the multilayer film is observed two-dimensionally from one side (the side connecting B and B'), and the end (B or B') of the other side (the side connecting B and B') (because it is the side when observed two-dimensionally, the side connecting A and A' and the side connecting B and B' are both considered to be on the same plane). Note that when the roll diameter exceeds 7 cm, it is considered that there is almost no curl. In other words, the roll diameter of a film that is not curled is considered to be more than 7 cm. The winding diameter is a parameter that indicates the overall balance between the moisture absorbing property of the EVOH layer and the residual stress due to stretching, and when the winding diameter is 14 mm or more, the converting suitability is surprisingly good. The winding diameter can be adjusted in step (III) described later, and the winding diameter can be made 14 mm or more by treating the multilayer film after stretching under conditions of a temperature of 28°C to 60°C and a humidity of 65% RH or more.

[0015] <Barrier layer (A)> The multilayer film of the present invention has a barrier layer (A) mainly composed of EVOH (a) as the outermost layer, and thus has good gas barrier properties. In addition, since the barrier layer (A) has good affinity with the inorganic vapor deposition layer (I) described below, a vapor-deposited multilayer film having the inorganic vapor deposition layer (I) adjacent to the exposed surface of the barrier layer (A) exhibits even better gas barrier properties, and tends to maintain its gas barrier properties even when subjected to physical stress such as bending. From the viewpoint of producing such a vapor-deposited multilayer film, it is preferable to provide the barrier layer (A) as the outermost layer. Note that a plurality of barrier layers (A) may be provided, and in that case, it is sufficient that at least one barrier layer (A) is provided as the outermost layer.

[0016] EVOH (a) is usually obtained by saponifying an ethylene-vinyl ester copolymer obtained by polymerizing ethylene and a vinyl ester. The ethylene unit content of EVOH (a) is 20 to 50 mol%. When the ethylene unit content is 20 mol% or more, the melt moldability of EVOH (a) is improved, and the recyclability of the multilayer structure of the present invention is improved. The ethylene unit content is preferably 22 mol% or more. On the other hand, when the ethylene unit content is 50 mol% or less, the gas barrier property of the multilayer film of the present invention is improved and the converting suitability tends to be good. The ethylene unit content is preferably 40 mol% or less, more preferably 35 mol% or less, and even more preferably 30 mol% or less, and may be 25 mol% or less. When the ethylene unit content is 25 mol% or less, a multilayer film having good converting suitability can be produced even if the temperature and humidity required in the step (III) described below are reduced.

[0017] The saponification degree of EVOH (a) is 90 mol% or more. The saponification degree means the ratio of the number of vinyl alcohol units to the total number of vinyl alcohol units and vinyl ester units in EVOH (a). When the saponification degree is 90 mol% or more, the gas barrier property of the composite multilayer film of the present invention is improved. The saponification degree is preferably 95 mol% or more, more preferably 99 mol% or more, and even more preferably 99.9 mol% or more. The ethylene unit content and saponification degree of EVOH (a) are 1 It can be determined by H-NMR measurement.

[0018] EVOH (a) may be a mixture of two or more kinds of EVOH having different ethylene unit contents. In this case, the difference in ethylene unit content between EVOH having the most different ethylene unit contents is preferably 30 mol% or less, more preferably 20 mol% or less, even more preferably 15 mol% or less, and may be 3 mol% or more. Similarly, EVOH (a) may be a mixture of two or more kinds of EVOH having different saponification degrees. In this case, the difference in saponification degree between EVOH having the most different ethylene unit contents is preferably 7% or less, more preferably 5% or less, and may be 0.5 mol% or more. When it is desired to achieve both gas barrier property and recyclability at a higher level, it is preferable to mix EVOH (a1) having an ethylene unit content of 22 mol% or more and less than 34 mol% and a saponification degree of 99 mol% or more and EVOH (a2) having an ethylene unit content of 34 mol% or more and less than 50 mol% and a saponification degree of 99 mol% or more at a blending mass ratio (a1 / a2) of 80 / 20 to 98 / 2 and use the mixture as EVOH (a).

[0019] EVOH (a) may contain other monomer units than ethylene, vinyl ester, and vinyl alcohol, so long as the effects of the present invention are not impaired. In particular, by introducing a modified group containing a primary hydroxyl group having a specific structure, it may be possible to achieve a high level of both gas barrier properties and moldability of EVOH (a). 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 none. Examples of such other monomers include 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, acrylamidopropanesulfonic acid and its salts, acrylamidopropyldimethylamine and its salts (e.g., quaternary salts); methacrylamide, N-methylmethacrylamide, N-ethylmethacrylamide, methacrylamidopropanesulfonic acid and its salts, methacrylamidopropyldimethylamine and its salts (e.g., quaternary salts); methyl vinyl ether, ethyl vinyl ether, n-propyl vinyl ether, i-propyl vinyl ether, vinyl ethers such as acrylonitrile, n-butyl vinyl ether, i-butyl vinyl ether, t-butyl vinyl ether, dodecyl vinyl ether, stearyl vinyl ether, 2,3-diacetoxy-1-vinyloxypropane, and the like; vinyl cyanides such as acrylonitrile, methacrylonitrile, and the like; vinyl halides such as vinyl chloride, vinyl fluoride, and the like; vinylidene halides such as vinylidene chloride, vinylidene fluoride, and the like; allyl compounds such as allyl acetate, 2,3-diacetoxy-1-allyloxypropane, and allyl chloride, and the like; unsaturated dicarboxylic acids and salts or esters thereof such as maleic acid, itaconic acid, and fumaric acid, and the like; vinyl silane compounds such as vinyltrimethoxysilane, and the like; isopropenyl acetate, 1,3-diacetoxy-2-methylenepropane, 1,3-dipropionyloxy-2-methylenepropane, and 1,3-dibutyronyloxy-2-methylenepropane, and the like.

[0020] The melt flow rate (MFR) of EVOH(a) measured in accordance with JIS K7210(2014) (210°C, under a load of 2.16 kg) is preferably 0.2 to 25 g / 10 min. The MFR of EVOH(a) is more preferably 0.5 g / 10 min or more, and even more preferably 0.8 g / 10 min or more. On the other hand, the MFR of EVOH(a) is more preferably 20 g / 10 min or less, more preferably 15 g / 10 min or less, even more preferably 10 g / 10 min or less, and particularly preferably 3 g / 10 min or less. When the MFR of EVOH(a) is in the above range, the melt moldability of EVOH(a) and the pulverized product of the multilayer structure containing EVOH(a) is improved.

[0021] <Polyvalent metal ions (d)> The barrier layer (A) preferably contains 10 to 300 ppm of at least one polyvalent metal ion (d) selected from the group consisting of magnesium ions, calcium ions, and zinc ions. When the barrier layer (A) contains 10 ppm or more of the polyvalent metal ion (d), there is a tendency to suppress appearance defects such as thickening and the generation of gels or bumps during melt molding. On the other hand, when the content of the polyvalent metal ion (d) is 300 ppm or less, there is a tendency to suppress excessive decomposition and coloration during melt molding. In addition, when recycling the multilayer structure of the present invention, a crosslinking reaction of the resin may progress during melt molding of the pulverized product of the multilayer structure, causing thickening and gelling. However, by containing a certain amount of the polyvalent metal ion (d), thickening, gelling, and adhesion of the resin to the screw are suppressed. From this viewpoint, the content of the polyvalent metal ion (d) is preferably 20 to 200 ppm, more preferably 30 to 150 ppm. In particular, the barrier layer (A) preferably contains calcium ions or zinc ions as the polyvalent metal ions (d). In addition, by controlling the content ratio of the polyvalent metal ion (d) to the carboxylic acid described below, the melt moldability and coloring resistance can be further improved.

[0022] Examples of polyvalent metal compounds that provide the polyvalent metal ions (d) include aliphatic carboxylates, aromatic carboxylates, carbonates, hydrochlorides, nitrates, sulfates, phosphates, hydroxides, and metal complexes of magnesium, calcium, and zinc. Among these, aliphatic carboxylates and hydroxides are more preferred because they are easily available and easy to handle. As aliphatic carboxylates, acetates, caprylates, and stearates are preferred.

[0023] <Higher aliphatic carboxylic acids (e)> The barrier layer (A) preferably contains 100 to 4000 ppm of a higher aliphatic carboxylic acid (e) having 8 to 30 carbon atoms. The higher aliphatic carboxylic acid (e) may be contained in part or in whole in the form of a salt, or may be contained as a salt of a polyvalent metal ion (d) or an alkali metal ion described later. The higher aliphatic carboxylic acid (e) is preferably caprylic acid or stearic acid. The multilayer film of the present invention has the barrier layer (A) as the outermost layer, and it is considered that the higher aliphatic carboxylic acid (e) acts as a lubricant with the die metal surface in the die, thereby suppressing the occurrence of poor appearance due to uneven thickness of the multilayer film and gels and bumps due to retained resin. For this reason, the barrier layer (A) preferably contains 100 ppm or more of the higher aliphatic carboxylic acid (e). On the other hand, if the content of the higher aliphatic carboxylic acid (e) is 4000 ppm or less, thickening of the barrier layer (A) during melt molding is suppressed, and interlayer adhesion with the adhesive layer (B) described later tends to be maintained. From these viewpoints, the content of the higher aliphatic carboxylic acid (e) is more preferably from 200 to 3000 ppm, and further preferably from 300 to 2500 ppm.

[0024] The barrier layer (A) may contain other components other than EVOH (a), polyvalent metal ions (d) and higher aliphatic carboxylic acids (e) as long as the effects of the present invention are not impaired. Examples of other components include alkali metal ions, alkaline earth metal ions and transition metal ions other than polyvalent metal ions (d), carboxylic acids (monocarboxylic acids, polyvalent carboxylic acids) other than higher aliphatic carboxylic acids (e), thermoplastic resins other than EVOH (a), phosphoric acid compounds, boron compounds, oxidation promoters, antioxidants (hindered phenol compounds, etc.), plasticizers, heat stabilizers (melt stabilizers), photoinitiators, deodorants, ultraviolet absorbers, antistatic agents, lubricants, colorants, fillers, desiccants, bulking agents, pigments, dyes, processing aids, flame retardants, antifogging agents, etc. It is preferable to contain alkali metal ions, carboxylic acids and / or phosphoric acid compounds from the viewpoint of suppressing the generation of bumps and coloring when the pulverized product of the multilayer structure including the barrier layer (A) is melt-molded. Furthermore, by containing a boron compound, the melt viscosity of the barrier layer (A) and the pulverized product of the multilayer structure including the barrier layer (A) can be controlled.

[0025] <Alkali metal ions> The barrier layer (A) may contain 40 to 500 ppm of alkali metal ions. When the barrier layer (A) contains alkali metal ions in the above range, the interlayer adhesion with the adhesive layer (B) described later tends to be significantly improved. If the amount of alkali metal ions is too small, the layer is likely to thicken during melt molding, causing poor appearance such as gels and bumps, and the interlayer adhesion with the adhesive layer (B) described later may decrease. On the other hand, if the amount of alkali metal ions is too large, the layer may be excessively decomposed during melt molding, or coloring may become a problem. From this viewpoint, the lower limit of the content of the alkali metal ions is preferably 80 ppm, more preferably 120 ppm. The upper limit of the content of the alkali metal ions is preferably 400 ppm, more preferably 300 ppm. In addition, by controlling the content ratio of the alkali metal ions to the carboxylic acid described later, the melt moldability and coloring resistance can be further improved.

[0026] Examples of alkali metal ions include lithium, sodium, potassium, rubidium, and cesium ions, but sodium or potassium ions are preferred from the viewpoint of industrial availability. In particular, by using potassium ions, it may be possible to achieve high levels of both the hue of the barrier layer (A) and the interlayer adhesion with the adhesive layer (B) described below. These ions may be used alone or in combination of two or more.

[0027] Examples of alkali metal compounds that provide alkali metal ions include aliphatic carboxylates, aromatic carboxylates, carbonates, hydrochlorides, nitrates, sulfates, phosphates, hydroxides, and metal complexes of alkali metals such as lithium, sodium, and potassium. Among these, aliphatic carboxylates and phosphates are more preferred because they are easily available and easy to handle. As aliphatic carboxylates, acetates, caprylates, and stearates are preferred.

[0028] <Carboxylic acid> The barrier layer (A) preferably contains a carboxylic acid other than the higher aliphatic carboxylic acid (e). The lower limit of the carboxylic acid content is preferably 50 ppm, more preferably 100 ppm. On the other hand, the upper limit of the carboxylic acid content is preferably 400 ppm, more preferably 350 ppm. When the carboxylic acid content is 50 ppm or more, the coloring resistance tends to be good. On the other hand, when the carboxylic acid content is 400 ppm or less, the interlayer adhesion tends to be maintained and the generation of odors tends to be suppressed.

[0029] The pKa of the carboxylic acid is preferably 3.5 to 5.5. When the pKa of the carboxylic acid is within the above range, the pH buffering ability of the resulting barrier layer (A) is increased, and the melt moldability is further improved, and coloring due to acidic or basic substances can be further improved.

[0030] The carboxylic acid may be a monovalent carboxylic acid. These may be used alone or in combination of two or more. The monovalent carboxylic acid is a compound having one carboxyl group in the molecule. Examples of monovalent carboxylic acids having a pKa in the range of 3.5 to 5.5 include, but are not limited to, 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 a substituent such as a hydroxyl group, an amino group, or a halogen atom. Among them, acetic acid is preferred because of its high safety and ease of availability and handling.

[0031] The carboxylic acid may be a polycarboxylic acid. When the carboxylic acid is a polycarboxylic acid, the coloring resistance at high temperatures and the coloring resistance of the melt-molded product of the crushed material of the obtained multilayer structure may be further improved. The polycarboxylic acid compound preferably has three or more carboxyl groups. In this case, the coloring resistance may be more effectively improved. The polycarboxylic acid is a compound having two or more carboxyl groups in the 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, and examples of the polycarboxylic acid include 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 2=5.41), pimelic acid (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), aspartic acid (pKa=3.90), etc.

[0032] <Phosphate compounds> The barrier layer (A) may further contain a phosphate compound. The lower limit of the content of the phosphate compound is preferably 5 ppm in terms of phosphate radicals. On the other hand, the upper limit of the content of the phosphate compound is preferably 100 ppm in terms of phosphate radicals. By containing the phosphate compound within this range, coloration of the resulting barrier layer (A) and the melt-molded product of the pulverized product of the resulting multilayer structure may be suppressed, and thermal stability may be improved.

[0033] As the phosphoric acid compound, various acids such as phosphoric acid and phosphorous acid and their salts can be used. The phosphate may be any of primary phosphate, secondary phosphate, and tertiary phosphate. The cationic species of the phosphate is not particularly limited, but the cationic species is preferably an alkali metal or an alkaline earth metal. Among them, as the phosphoric acid compound, sodium dihydrogen phosphate, potassium dihydrogen phosphate, disodium hydrogen phosphate, and dipotassium hydrogen phosphate are preferred.

[0034] <Boron compounds> The barrier layer (A) may further contain a boron compound. When the boron compound is contained, the lower limit of the content in the barrier layer (A) is preferably 50 ppm, more preferably 100 ppm, calculated as boron element. On the other hand, the upper limit of the content of the boron compound in the barrier layer (A) is preferably 400 ppm, more preferably 200 ppm, calculated as boron element. By containing the boron compound in this range, the thermal stability of the barrier layer (A) and the pulverized product of the obtained multilayer structure during melt molding may be improved, and the generation of gels and bumps may be suppressed. In addition, the drawdown resistance and neck-in resistance during film formation may be improved, and the mechanical properties of the obtained molded product may be improved. It is presumed that these effects are due to the occurrence of a chelate interaction between the EVOH (a) and the boron compound.

[0035] Examples of boron compounds include boric acid, boric acid esters, borate salts, and boron hydrides. 3 BO 3), boric acid such as metaboric acid or tetraboric acid; boric acid esters such as trimethyl borate or triethyl borate; alkali metal salts or alkaline earth metal salts of the above-mentioned boric acid, borate salts such as borax, etc. Among these, orthoboric acid is preferred.

[0036] The barrier layer (A) may further contain a thermoplastic resin other than EVOH (a). Examples of the thermoplastic resin other than EVOH (a) include various polyolefins (polyethylene, polypropylene, poly1-butene, poly4-methyl-1-pentene, ethylene-propylene copolymers, copolymers of ethylene and α-olefins having 4 or more carbon atoms, copolymers of polyolefins and maleic anhydride, ethylene-vinyl ester copolymers, ethylene-acrylic acid ester copolymers, or modified polyolefins obtained by graft-modifying these with unsaturated carboxylic acids or their derivatives, etc.), various polyamides (nylon 6, nylon 6·6, nylon 6 / 66 copolymers, nylon 11, nylon 12, polymetaxylylene adipamide, etc.), various polyesters (polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, etc.), polyvinyl chloride, polyvinylidene chloride, polystyrene, polyacrylonitrile, polyurethane, polycarbonate, polyacetal, polyacrylate, and modified polyvinyl alcohol resins, etc. The content of the thermoplastic resin in the barrier layer (A) is usually less than 40 mass%, preferably less than 30 mass%, more preferably less than 20 mass%, even more preferably less than 10 mass%, may be less than 5 mass% or less than 1 mass%, and it is particularly preferable that the barrier layer (A) is substantially free of the thermoplastic resin.

[0037] The proportion of EVOH (a) in the resin constituting the barrier layer (A) is preferably 60% by mass or more, more preferably 70% by mass or more, even more preferably 80% by mass, even more preferably 90% by mass or more, particularly preferably 95% by mass or more, and may be 98% by mass or more or 99% by mass or more, and the resin constituting the barrier layer (A) may be substantially EVOH (a) only. The proportion of EVOH (a) in the barrier layer (A) is preferably 60% by mass or more, more preferably 70% by mass or more, even more preferably 80% by mass, even more preferably 90% by mass or more, particularly preferably 95% by mass or more, and may be 98% by mass or more or 99% by mass or more, and the barrier layer (A) may be substantially composed of EVOH (a) only.

[0038] The method for producing the barrier layer (A) is not particularly limited, but it can be produced by melt-kneading EVOH (a) and, if necessary, polyvalent metal ions (d), higher aliphatic carboxylic acid (e) and / or other components. Each component may be blended in a solid state such as powder or as a melt, or may be blended as a solute contained in a solution or a dispersoid contained in a dispersion. As the solution and dispersion, an aqueous solution and an aqueous dispersion are preferable, respectively. For melt-kneading, a known mixing or kneading device such as a kneader-ruder, an extruder, a mixing roll, or a Banbury mixer can be used. The temperature range during melt-kneading can be appropriately adjusted depending on the melting point of the EVOH (a) and each component used, and is usually 150 to 250°C. In addition, the barrier layer (A) may be produced by adding some components to EVOH (a) in advance and then melt-kneading other components required as described above. As a method for adding some components to EVOH (a) in advance, EVOH (a) is immersed as pellets or powder in a solution in which the added components are dissolved.

[0039] <Adhesive layer (B)> The multilayer film of the present invention has an adhesive layer (B) containing an adhesive resin (b) having a melting point of less than 150°C as a main component. By including the adhesive layer (B) in the multilayer film of the present invention, a multilayer film having excellent appearance and interlayer adhesion tends to be obtained. The adhesive resin (b) may be a carboxylic acid-modified polyolefin resin obtained by graft-polymerizing an unsaturated carboxylic acid or its derivative such as maleic anhydride to a polyolefin resin. The melting point of the adhesive resin (b) mainly depends on the polyolefin resin before the carboxylic acid modification. The contents described below regarding the polyolefin resin (c) can be applied as they are to the polyolefin resin.

[0040] The proportion of the carboxylic acid-modified polyolefin resin in the adhesive resin (b) is preferably 70% by mass or more, more preferably 80% by mass or more, and even more preferably 95% by mass or more, and may be substantially composed of only the carboxylic acid-modified polyolefin resin. The proportion of the adhesive resin (b) in the adhesive layer (B) is preferably 70% by mass or more, more preferably 80% by mass or more, and even more preferably 95% by mass or more, and may be 97% by mass or more or 99% by mass or more, and may be substantially composed of only the adhesive resin (b).

[0041] <Moisture-proof layer (C)> The multilayer film of the present invention has a moisture-proof layer (C) containing a polyolefin resin (c) having a melting point of less than 150°C as a main component. The polyolefin resin (c) is not particularly limited as long as it is a polyolefin having a melting point of less than 150°C, and examples thereof include polyethylene resins such as linear low-density polyethylene, low-density polyethylene, medium-density polyethylene, and high-density polyethylene; vinyl ester resins; ethylene-propylene copolymers; propylene-α-olefin copolymers (α-olefins having 4 to 20 carbon atoms); olefins such as polybutene and polypentene, or copolymers thereof; and chlorinated polyethylene. From the viewpoint of improving the recyclability of the multilayer structure containing the polyolefin resin (c), the polyolefin resin (c) preferably contains a polyethylene resin as a main component, and more preferably is a polyethylene resin. Since polyethylene resins are widely used in packaging materials regardless of whether they have gas barrier properties or not, recycling infrastructures for them have been widely established in various countries. When the polyolefin resin (c) contains a polyethylene resin as a main component, the polyethylene resin is preferably at least one selected from linear low-density polyethylene, low-density polyethylene, medium-density polyethylene, and high-density polyethylene, and more preferably at least one selected from linear low-density polyethylene and low-density polyethylene, or a mixture of at least one selected from linear low-density polyethylene and low-density polyethylene and high-density polyethylene.

[0042] From the viewpoint of making the effects of the present invention more remarkable, the melting point of the polyolefin resin (c) is preferably less than 140° C., more preferably less than 130° C. On the other hand, from the viewpoint of processability during melt molding and secondary processing such as stretching, and from the viewpoint of heat resistance as a packaging material, the melting point of the polyolefin resin (c) is preferably 80° C. or higher, more preferably 90° C. or higher. In addition, from the viewpoint of improving melt moldability, the MFR (190° C., under a load of 2160 g) of the polyolefin resin (c) measured in accordance with the method described in JIS K7210 (2014) is preferably 0.1 to 30 g / 10 min, more preferably 0.3 to 25 g / 10 min, and even more preferably 0.5 to 20 g / 10 min.

[0043] The polyolefin resin (c) preferably contains a polyethylene resin as a main component, and the content of the polyethylene resin in the polyolefin resin (c) is more preferably 70% by mass or more, even more preferably 80% by mass or more, and particularly preferably 95% by mass or more, and the polyolefin resin (c) may be substantially composed of only the polyethylene resin. The proportion of the polyolefin resin (c) in the moisture-proof layer (C) is preferably 70% by mass or more, more preferably 80% by mass or more, and even more preferably 95% by mass or more, and the polyolefin resin (c) may be substantially composed of only the polyolefin resin (c).

[0044] The adhesive layer (B) and the moisture-proof layer (C) contain adhesive resin (b) and polyolefin resin (c) as main components, respectively, but these layers may contain other components such as antioxidants, plasticizers, heat stabilizers (melt stabilizers), photoinitiators, deodorants, UV absorbers, antistatic agents, lubricants, colorants, fillers, desiccants, bulking agents, pigments, dyes, processing aids, flame retardants, and antifogging agents, as long as the effects of the present invention are not impaired. However, the total amount of these components is less than 50% by mass for each layer, preferably less than 40% by mass, more preferably less than 30% by mass, even more preferably less than 20% by mass, and particularly preferably less than 10% by mass.

[0045] In the multilayer film of the present invention, the barrier layer (A), the adhesive layer (B) and the moisture-proof layer (C) may be provided in one or more layers. When multiple layers are provided, each layer may be made of the same material or different materials.

[0046] <Multilayer film> The layer structure of the multilayer film of the present invention is not particularly limited as long as it has a structure in which a barrier layer (A), an adhesive layer (B) and a moisture-proof layer (C) are laminated in this order, and at least one barrier layer (A) is located as the outermost layer of the multilayer film, and for example, the following multilayer film structure is exemplified. The barrier layer (A) is represented as "layer (A)", the adhesive layer (B) as "layer (B)", and the moisture-proof layer (C) as "layer (C)". In addition, " / " means that the layers on both sides are directly laminated. Examples of the layer structure of the multilayer film of the present invention include layer (C) / layer (B) / layer (A), layer (C) / layer (B) / layer (A) / layer (B) / layer (A), layer (C) / layer (B) / layer (A) / layer (B) / layer (C) / layer (B) / layer (A), and the like. Among them, layer (C) / layer (B) / layer (A) is preferable from the viewpoint of industrial productivity.

[0047] The total thickness of the multilayer film of the present invention can be appropriately set depending on the application. The total thickness is preferably 10 μm or more, more preferably 15 μm or more. When the total thickness is 10 μm or more, industrial productivity and mechanical properties tend to be improved. In addition, the total thickness is preferably 100 μm or less, more preferably 50 μm or less. When the total thickness is 100 μm or less, industrial productivity and economic efficiency tend to be improved. The preferred total thickness of the multilayer film means the thickness after stretching.

[0048] The thickness of the barrier layer (A) is preferably 0.4 μm or more, more preferably 0.8 μm or more, and may be 1 μm or more. When the thickness of the barrier layer (A) is 0.4 μm or more, the gas barrier property tends to be improved. Furthermore, the thickness of the barrier layer (A) is preferably 10 μm or less, more preferably 6 μm or less, and may be 4 μm or less. When the thickness of the barrier layer (A) is 10 μm or less, the appearance characteristics (film surface) after stretching tend to be good. The suitable thickness of the barrier layer (A) means the thickness after stretching.

[0049] The thickness of the adhesive layer (B) is preferably 0.4 μm or more, more preferably 0.8 μm or more, and may be 1 μm or more. When the thickness of the adhesive layer (B) is 0.4 μm or more, the adhesive strength tends to be improved. In addition, the thickness of the adhesive (B) is preferably 10 μm or less, more preferably 6 μm or less, and may be 4 μm or less. When the thickness of the adhesive layer (B) is 10 μm or less, the appearance characteristics (film surface) after stretching tend to be good. The suitable thickness of the adhesive (B) means the thickness after stretching.

[0050] The thickness of the moisture-proof layer (C) is preferably 5 μm or more, more preferably 10 μm or more, and may be 20 μm or more. When the thickness of the moisture-proof layer (C) is 5 μm or more, the moisture-proof property tends to be improved. The thickness of the moisture-proof layer (C) is preferably 100 μm or less, more preferably 50 μm or less, and may be 30 μm or less. The suitable thickness of the moisture-proof layer (C) means the thickness after stretching.

[0051] The ratio of the thickness of the barrier layer (A) to the total thickness of all layers of the multilayer film of the present invention is preferably 30% or less, more preferably 20% or less, and may be 10% or less, or 5% or less, from the viewpoints of industrial productivity and mechanical properties.

[0052] The multilayer film of the present invention is stretched at least 3 times in one direction. If the multilayer film of the present invention is stretched less than 3 times, thickness unevenness due to stretching tends to occur and gas barrier properties tend to decrease. On the other hand, the upper limit of the stretching ratio of the multilayer film of the present invention is usually 12 times. The multilayer film of the present invention is preferably stretched at least 4 times in one direction, more preferably 5 times or more. In addition, the multilayer film of the present invention is preferably stretched at least 10 times in one direction, more preferably 8 times or less. The multilayer film of the present invention may be stretched in one direction or biaxially, but from the viewpoint of economy and ease of tearing the multilayer film (ease of opening the packaging material when used as a packaging material), it is preferably uniaxially stretched, and particularly preferably uniaxially stretched in the longitudinal direction (MD direction). In this case, it is preferable that the film is not substantially stretched in the transverse direction (TD direction).

[0053] The method for producing the multilayer film of the present invention preferably includes, for example, a step (I) of producing an unstretched multilayer film having a barrier layer (A), an adhesive layer (B) and a moisture-proof layer (C) in this order, a step (II) of stretching the obtained unstretched multilayer film at least uniaxially to produce a pre-treated multilayer film, and a step (III) of treating the pre-treated multilayer film after stretching under conditions of a temperature of 28° C. to 60° C. and a humidity of 65% RH to 95% RH. A preferred production method of the present invention is described in detail below, but the present invention is not limited thereto.

[0054] In step (I), an unstretched multilayer film having a barrier layer (A), an adhesive layer (B), and a moisture-proof layer (C) in this order is formed. The method for producing the unstretched multilayer film is not particularly limited, and generally, a conventional coextrusion method in which each resin is extruded from a separate die or a common die and laminated can be used. As the die, either a circular die or a T-die can be used, and examples of the method include inflation molding and cast molding, but inflation molding is preferred in terms of productivity.

[0055] In step (II), the unstretched multilayer film obtained in step (I) is stretched at least uniaxially. The stretching method is not particularly limited, and examples thereof include tenter stretching, tubular stretching, and roll stretching. From the viewpoint of production cost, uniaxial stretching by roll stretching is preferred. In addition, when the multilayer film of the present invention is an inflation molding, roll stretching is preferred from the viewpoint of easily stretching the folded cylindrical multilayer film after inflation molding in uniaxial direction. The temperature range for stretching is generally 50°C to 130°C, and more preferably 100°C to 120°C.

[0056] In step (III), the stretched untreated multilayer film is treated under conditions of a temperature of 28° C. to 60° C. and a humidity of 65% RH or more. The temperature during treatment is preferably 35° C. to 50° C. The humidity during treatment is preferably 67% RH to 95% RH, and may be 75% RH to 93% RH. By carrying out such treatment, the converting suitability of the multilayer film of the present invention tends to be improved. Although not always applicable, when the ethylene unit content of EVOH is low, the temperature and humidity required for treating the stretched multilayer film tend to be reduced.

[0057] A preferred embodiment of the multilayer film of the present invention is a vapor-deposited multilayer film in which the inorganic vapor-deposited layer (I) is adjacent to the exposed surface side of the barrier layer (A) of the multilayer film of the present invention. Adjacent here means directly in contact. Since the barrier layer (A) has good affinity with the inorganic vapor-deposited layer (I), the vapor-deposited multilayer film of the present invention has high gas barrier properties and tends to maintain good gas barrier properties even when subjected to physical stress such as bending.

[0058] <Inorganic vapor deposition layer (I)> The inorganic vapor deposition layer (I) is usually a layer having a barrier property against oxygen and water vapor. Therefore, the vapor deposition multilayer film of the present invention tends to have good gas barrier property by including the inorganic vapor deposition layer (I). The inorganic vapor deposition layer (I) can be formed by vapor deposition of an inorganic material. Examples of the inorganic material include metals (e.g., aluminum), metal oxides (e.g., silicon oxide, aluminum oxide), metal nitrides (e.g., silicon nitride), metal nitride oxides (e.g., silicon oxynitride), and metal carbonitrides (e.g., silicon carbonitride). Among these, the inorganic vapor deposition layer (I) formed of aluminum, aluminum oxide, silicon oxide, magnesium oxide, or silicon nitride is preferred from the viewpoint of industrial productivity, and the inorganic vapor deposition layer (I) formed of aluminum is more preferred. Even if the metal vapor deposition layer is aluminum, oxidation may occur irreversibly and aluminum oxide may be partially contained. When aluminum oxide is partially contained in the metal vapor deposition layer, the amount of aluminum atoms constituting the metal vapor deposition layer (Al mol ) to the amount of oxygen atoms (O mol ) ratio (O mol / Al mol ) is preferably 0.5 or less, more preferably 0.3 or less, even more preferably 0.1 or less, and particularly preferably 0.05 or less.

[0059] The method for forming the inorganic vapor deposition layer (I) is not particularly limited, and examples thereof include physical vapor deposition methods such as vacuum deposition (e.g., resistance heating deposition, electron beam deposition, molecular beam epitaxy, etc.), sputtering, and ion plating; and chemical vapor deposition methods such as thermal chemical vapor deposition (e.g., catalytic chemical vapor deposition), photochemical vapor deposition, plasma chemical vapor deposition (e.g., capacitively coupled plasma, inductively coupled plasma, surface wave plasma, electron cyclotron resonance, dual magnetron, atomic layer deposition, etc.), and metalorganic vapor deposition.

[0060] The inorganic vapor deposition layer (I) is provided adjacent to the surface side of the barrier layer (A) of the multilayer film of the present invention. By providing the inorganic vapor deposition layer (I) on the barrier layer (A), the gas barrier property and the gas barrier property even after physical stress such as bending tend to be good. The average thickness of the inorganic vapor deposition layer (I) is preferably 150 nm or less, more preferably 120 nm or less, and even more preferably 100 nm or less. The average thickness of the inorganic vapor deposition layer (I) 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 vapor deposition layer (I) is the average value of thicknesses at any 10 points on the cross section of the inorganic vapor deposition layer (I) measured by an electron microscope. From the viewpoint of reducing coloration of the recovered composition of the multilayer structure, when the multilayer structure has a plurality of inorganic vapor deposition layers (I), the total thickness of the inorganic vapor deposition layers (I) is preferably 1 μm or less.

[0061] <Multilayer structure> The multilayer film or vapor-deposited multilayer film of the present invention itself can be used as a packaging material having gas barrier properties, but by forming a multilayer structure by laminating at least one resin layer (R) containing a thermoplastic resin (r) as a main component, various functions as a packaging material such as designability and heat sealability can be imparted. The thermoplastic resin (r) is not particularly limited, and examples thereof include linear low-density polyethylene, low-density polyethylene, medium-density polyethylene, high-density polyethylene, vinyl ester resin, ethylene-propylene copolymer, polypropylene, propylene-α-olefin copolymer (α-olefin having 4 to 20 carbon atoms), polybutene, polypentene, and other olefins alone or copolymers thereof, polyamides such as nylon 6 and nylon 6,6, polyesters such as polyethylene terephthalate, polybutylene terephthalate, and polyethylene naphthalate, polystyrene, polyvinyl chloride, polyvinylidene chloride, acrylic resin, polycarbonate, chlorinated polyethylene, and chlorinated polypropylene. Among them, polyolefin is preferred from the viewpoint of excellent moisture resistance, mechanical properties, economical efficiency, heat sealability, etc., and polyamide and polyester are preferred from the viewpoint of excellent mechanical properties, heat resistance, etc. In order to obtain a multilayer structure with particularly excellent recyclability, the thermoplastic resin (r) is preferably the same type as the above-mentioned polyolefin resin (c), that is, a polyolefin resin having a melting point of less than 150°C, more preferably containing a polyethylene resin as a main component, and even more preferably a polyethylene resin. Therefore, in order to obtain a multilayer structure with excellent recyclability, the polyolefin resin (c) and the thermoplastic resin (r) preferably contain a polyethylene resin as a main component, and more preferably a polyethylene resin. Such a resin layer (R) may be unstretched, or may be stretched or rolled in a uniaxial or biaxial direction. From the viewpoint of improving mechanical strength, a biaxially stretched layer is preferred, and from the viewpoint of improving heat sealability, a nonstretched layer is preferred.

[0062] The method for forming the resin layer (R) is not particularly limited, but it is generally formed by melt extrusion using an extruder. As the die, either a circular die or a T-die can be used. The method for stretching in the uniaxial or biaxial direction is also not particularly limited, and the film can be produced by stretching in the flow direction of the film and / or the direction perpendicular to the flow direction, i.e., in the width direction, by a conventionally known stretching method such as roll-type uniaxial stretching, tubular-type simultaneous biaxial stretching, tenter-type sequential biaxial stretching, and tenter-type simultaneous biaxial stretching. The stretching ratio is preferably 8 to 60 times in area from the viewpoint of the uniformity of the thickness of the obtained layer and mechanical strength. The area ratio is more preferably 55 times or less, and even more preferably 50 times or less. The area ratio is 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 layer may easily break during stretching.

[0063] The thickness of the resin layer (R) is preferably 10 to 200 μm from the viewpoint of industrial productivity. Specifically, the thickness is more preferably 10 to 150 μm in the case of a non-oriented layer, and more preferably 10 to 50 μm in the case of a biaxially oriented layer.

[0064] The multilayer structure of the present invention has a total thickness of preferably 300 μm or less, and may have a total thickness of 200 μm or less. With a total thickness in the above range, the multilayer structure of the present invention is lightweight and flexible, and is therefore preferably used for soft packaging. In addition, the amount of resin used in the multilayer structure is small, and environmental load is reduced.

[0065] The thickness of each layer in the multilayer structure of the present invention may be appropriately adjusted depending on the application, but from the viewpoints of suppressing coloration during melt molding of the pulverized material, improving thermal stability during melt molding, and suppressing the generation of bumps, at least one layer of the moisture-proof layer (C) and the resin layer (R) contains a polyethylene resin as a main component, and the ratio of the total thickness of the layers containing a polyethylene resin as a main component to the total thickness of the multilayer structure is preferably 0.75 or more, more preferably 0.85 or more. On the other hand, from the viewpoint of improving the gas barrier property, the ratio is preferably 0.98 or less.

[0066] The method for laminating the resin layer (R) on the multilayer film of the present invention is not particularly limited, and examples thereof include extrusion lamination, coextrusion lamination, dry lamination, etc. When laminating the resin layer (R) on the multilayer film, an adhesive layer may be provided. The adhesive layer can be formed by applying a known adhesive and drying it. The adhesive is preferably a two-liquid reactive polyurethane adhesive in which a polyisocyanate component and a polyol component are mixed and reacted. The thickness of the adhesive layer is not particularly limited, but is preferably 1 to 5 μm, more preferably 2 to 4 μm.

[0067] The layer configuration of the multilayer structure of the present invention is not particularly limited, but may be, for example, the following multilayer structure configuration. The barrier layer (A) is represented as "layer (A)", the adhesive layer (B) as "layer (B)", the moisture-proof layer (C) as "layer (C)", and the resin layer (R) as "layer (R)". " / " means that the layers on both sides are directly laminated, and " / / " means that the layers on both sides are laminated directly or via an adhesive layer. Examples of the layer structure of the multilayer film of the present invention include layer (R) / / layer (C) / layer (B) / layer (A), layer (C) / layer (B) / layer (A) / / layer (R), layer (R) / / layer (C) / layer (B) / layer (A) / / layer (R), layer (R) / / layer (C) / layer (B) / layer (A) / layer (B) / layer (A), layer (C) / layer (B) / layer (A) / layer (B) / layer (A) / / layer (R), layer (R) / / layer (C) / layer (B) / layer (A) / layer (B) / layer (A) / / layer (R), layer (R) / / layer (C) / layer (B) / layer (A) / layer (B) / layer (A) / / layer (R), Examples of such a configuration include layer (R) / / layer (C) / layer (B) / layer (A) / layer (B) / layer (C) / layer (B) / layer (A), layer (C) / layer (B) / layer (A) / layer (B) / layer (C) / layer (B) / layer (A) / layer (R), layer (R) / / layer (C) / layer (B) / layer (A) / layer (B) / layer (C) / layer (B) / layer (A) / / layer (R), and among these, layer (C) / layer (B) / layer (A) / layer (R) is preferred from the viewpoints of industrial productivity and gas barrier properties.

[0068] The multilayer structure of the present invention may have layers other than those described above, as long as the effects of the present invention are not impaired. Examples of the other layers include a recovery layer. In particular, it is preferable to reuse a recovery composition containing the recovered material of the multilayer structure of the present invention described below as a part or all of the recovery layer. Another example of the other layer is, for example, a printing layer. The printing layer may be included at any position of the multilayer structure of the present invention. Examples of the printing layer include a film obtained by applying a solution containing a pigment or dye and, if necessary, a binder resin, and drying it. Examples of the coating method of the printing layer include gravure printing and various coating methods using a wire bar, a spin coater, a die coater, etc. The thickness of the ink layer is not particularly limited, but is preferably 0.5 to 10 μm, more preferably 1 to 4 μm.

[0069] It is preferable to reuse scraps (ends or defective products) that are recovered during the production of the multilayer structure of the present invention. A method for recovering the multilayer structure of the present invention by crushing the multilayer structure of the present invention and then melt-molding it, and a recovered composition containing the recovered multilayer structure of the present invention are also preferred embodiments of the present invention.

[0070] When recovering the multilayer structure of the present invention, the recovered multilayer structure of the present invention is first pulverized. The pulverized recovered material may be melt-molded as it is to obtain a recovered composition, or may be melt-molded together with other components as necessary to obtain a recovered composition. A preferred component to be added to the recovered material is a polyolefin resin, and more preferably a polyethylene resin. As the polyolefin resin, the same type of polyolefin resin (c) as that used in the multilayer film of the present invention is used. The pulverized recovered material may be directly used to produce a molded product such as a multilayer structure, or the pulverized recovered material may be melt-molded to obtain pellets of the recovered composition, and the pellets may then be used to produce a molded product.

[0071] In the recovered composition, the mass ratio of EVOH (a) to polyolefin resin [EVOH (a) / polyolefin resin] is preferably 0.01 / 99.99 to 20 / 80. If the mass ratio is less than 0.01 / 99.99, the usage ratio of the recovered material may decrease. On the other hand, if the mass ratio exceeds 20 / 80, the melt moldability and mechanical properties of the recovered composition may decrease. From the viewpoint of improving the melt moldability and mechanical properties of the obtained recovered composition, the mass ratio is more preferably 15 / 85 or less, further preferably 10 / 90 or less, and may be 5 / 95 or less.

[0072] Since the multilayer structure of the present invention has gas barrier properties and converting suitability, it can be suitably used as a material for various types of packaging, such as food packaging, pharmaceutical packaging, industrial chemical packaging, and agricultural chemical packaging. In particular, a packaging material comprising the multilayer structure of the present invention can be suitably used as a packaging material with excellent recyclability. EXAMPLES

[0073] The present invention will be described in more detail below using examples, but the present invention is not limited to these examples in any way.

[0074] [Example 1] (1) Preparation of EVOH (a)-containing resin composition for barrier layer (A) EVOH-1 (ethylene unit content 27 mol%, saponification degree 99.99 mol%, MFR (210°C, 2.16 kg load) 4.0 g / 10 min, sodium acetate 250 ppm in terms of sodium ion, phosphate ion 30 ppm in terms of phosphate radical, boric acid 150 ppm in terms of boron element, no polyvalent metal ions) and magnesium stearate were melt-kneaded so that the magnesium ion content in the resulting resin composition was 50 ppm, to obtain resin composition pellets for the barrier layer (A). The extruder used for melt-kneading was a twin-screw extruder with D (mm) = 25, and a unidirectional fully intermeshing screw with L / D = 25 was used. The resin temperature was set to 220°C.

[0075] (2) Resin composition containing adhesive resin (b) for adhesive layer (B) Maleic anhydride modified polyethylene "ADMER (trademark) NF518" manufactured by Mitsui Chemicals Inc. (MFR (190°C, 2.16 kg load) 3.1 g / 10 min, melting point 121°C, density 0.91 g / cm 3 , acid value 1.8 mgKOH / g) was used as the adhesive resin (b) and as the resin composition pellets for the adhesive layer (B).

[0076] (3) Polyolefin resin (c)-containing resin composition for moisture-proof layer (C) DOW's low-density polyethylene "INNATE (trademark) TF80" (MFR (190°C, 2.16 kg load) 1.6 g / 10 min, melting point 124°C, density 0.926 g / cm 3 ) was used as it was as polyolefin resin (c) and as resin composition pellets for the moisture-proof layer (C).

[0077] (4) Preparation of multilayer film Using each of the resin composition pellets (1) to (3) above, a cylindrical unstretched multilayer film was produced under the following conditions using an inflation extrusion molding machine. The moisture-proof layer (C) was laminated in three layers with a thickness of 30 μm, resulting in one layer of moisture-proof layer (C) with a thickness of 90 μm. <Conditions for producing unstretched multi-layer film> Layer structure of unstretched multilayer film: [Outer side] Moisture-proof layer (C) / Adhesive layer (B) / Barrier layer (A) [Inner side] = 90 μm / 15 μm / 15 μm (total thickness 120 μm) Equipment: Dr Collin 5-type 5-layer inflation extrusion molding machine Die temperature: 210℃. Blow-up ratio: 2.7. Take-off speed: 4m / min. Film folding width: 25cm <Conditions of Moisture Proof Layer (C) Extruder 1> Extruder: 30φ single screw extruder (manufactured by Dr Collin). Rotation speed: 60 rpm. Extrusion temperature: feeding section / compression section / metering section = 170°C / 190°C / 210°C. <Conditions for Moisture Proof Layer (C) Extruder 2> Extruder: 20φ single screw extruder (manufactured by Dr Collin). Rotation speed: 70 rpm. Extrusion temperature: feeding section / compression section / metering section = 170°C / 190°C / 210°C. <Conditions of Moisture Proof Layer (C) Extruder 3> Extruder: 20φ single screw extruder (manufactured by Dr Collin). Rotation speed: 70 rpm. Extrusion temperature: feeding section / compression section / metering section = 170°C / 190°C / 210°C. <Conditions of the adhesive layer (B) extruder> Extruder: 20φ single screw extruder (Dr Collin). Rotation speed: 70 rpm. Extrusion temperature: feeding section / compression section / metering section = 170°C / 190°C / 210°C. <Barrier layer (A) extruder conditions> Extruder: 30φ single screw extruder (Dr Collin). Rotation speed: 24 rpm. Extrusion temperature: feeding section / compression section / metering section = 190°C / 210°C / 210°C.

[0078] From the obtained cylindrical unstretched multilayer film, an unstretched multilayer film with a length of 6 cm in the longitudinal direction and a width of 25 cm was cut out, and the film was uniaxially stretched 5 times in the longitudinal direction (MD direction) at 115°C using a stretching device (SDR-506WK) manufactured by Eto Corporation, to obtain an untreated multilayer film (moisture-proof layer (C) / adhesive layer (B) / barrier layer (A) = 18 μm / 3 μm / 3 μm).

[0079] An A4 size film edge was cut out from any position of the obtained untreated multilayer film, sandwiched between two sheets of A4 size plain paper, and fixed at the four corners with clips. This was left to stand in a thermostatic chamber at 40°C and 90% RH for 48 hours to obtain a multilayer film of the present invention. The thickness of the obtained multilayer film was 24 μm, and the thickness ratio of the barrier layer (A) in the multilayer film was 12.5%.

[0080] (5) Evaluation of reel diameter A 10 cm square film was cut out from any position of the multilayer film obtained in (4), and left to stand for 24 hours in an atmosphere of 20°C and 65% RH, after which the roll diameter was measured and evaluated according to the following criteria. The results are shown in Table 1. Judgment criteria A: 70mm or more B: 50mm or more and less than 70mm C: 33mm or more and less than 50mm D: 14mm or more, less than 33mm E: Less than 14mm

[0081] (6) Oxygen transmission rate of multilayer film For the multilayer film obtained in (4), the oxygen transmission rate was measured in accordance with the method described in JIS K 7126-2 (isobaric method; 2006) with the barrier layer (A) as the oxygen supply side. Specifically, the oxygen transmission rate (unit: cc / (m)) was measured using an oxygen transmission amount measuring device ("MOCON OX-TRAN2 / 21" manufactured by Modern Control) under the conditions of 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 gas barrier properties were measured and rated according to the following criteria. Nitrogen gas containing 2% by volume of hydrogen gas was used as the carrier gas. The results are shown in Table 1. A rating of F indicates that the gas barrier properties were insufficient. Judgment criteria A: 0.05cc / (m 2 ·day·atm) B: 0.05cc / (m 2 ·day · atm) or more, 0.1cc / (m 2 ·day·atm) C: 0.1cc / (m 2 ·day · atm) or more, 0.3cc / (m 2 ·day·atm) D: 0.3cc / (m 2 ·day · atm) or more, 1.5cc / (m 2 ·day·atm) E: 1.5cc / (m 2 ·day · atm) or more, 30cc / (m 2 ·day·atm) F: 30cc / (m 2 ·day · atm) or more

[0082] (7) Oxygen permeability of multilayer film after bending treatment The oxygen permeability of the multilayer film obtained in (4) above was measured after bending using a Gelbo Flex Tester (manufactured by Rigaku Kogyo Co., Ltd.). Specifically, the multilayer film was first formed into a cylinder with a diameter of 3.5 inches, both ends were gripped, and a twist of 330 degrees was applied in the first 3.5 inches of the stroke with an initial gripping distance of 7 inches, a gripping distance of 1 inch at maximum bending, and a straight horizontal movement was applied for the next 2.5 inches. This reciprocating motion was repeated 10 times at a speed of 30 times / min, and then the oxygen permeability was measured using the same method as above, and the degree of deterioration compared to the oxygen permeability before bending (the ratio of oxygen permeability after bending / oxygen permeability before bending) was evaluated according to the following criteria. The rating of E was determined to be insufficient bending resistance. Judgment criteria A: Less than 1.05 B: 1.05 or more, less than 1.1 C: 1.1 or more, less than 1.5 D: 1.5 or more, less than 3.0 E: 3.0 or higher

[0083] (8) Fabrication of multilayer structures A two-liquid reactive polyurethane adhesive (24 parts by mass of "Takelac (trademark) A-520" manufactured by Mitsui Chemicals, Inc. and 4 parts by mass of "Takenate (trademark) A-50" manufactured by Mitsui Chemicals, Inc.) was mixed with 37 parts by mass of ethyl acetate to prepare an adhesive solution. Next, a polyethylene film having a thickness of 50 μm ("TUX HZR-2" manufactured by Mitsui Chemicals Tohcello, Inc., melting point 127°C) was used as the resin layer (R), and the adhesive solution was applied to the corona-treated surface of the film with a wire bar so that the thickness after drying would be 3 μm. The film was then dried at 100°C for 5 minutes to form an adhesive layer, and the barrier layer (A) side of the multilayer film obtained in (4) above was laminated with the adhesive layer to prepare a multilayer structure. The thickness of the obtained multilayer structure was 77 μm, and the thickness ratio of the polyethylene resin layer in the multilayer structure was 91.0%.

[0084] (9) Converting suitability The multilayer structure obtained in (8) above was cut into A4 size pieces, and the appearance of the film was visually observed and the converting suitability was evaluated according to the following criteria: E was judged to be insufficient for converting suitability. Judgment criteria A: No wrinkles were observed B: The maximum wrinkle length is less than 5 mm and the number of wrinkles is less than 5 C: The maximum wrinkle length is less than 5 mm and the number of wrinkles is 5 or more D: Maximum wrinkle length is 5mm or more and less than 10mm E: Maximum wrinkle length is 10mm or more

[0085] (9) Evaluation of recyclability of multi-layer structures The multilayer structure obtained in (8) above was crushed to a size of 4 mm square or less, and the crushed product was mixed with low-density polyethylene (LDPE) "Novatec (trademark) LD LJ400" (MFR (190°C, 2.16 kg load) 1.5 g / 10 min, density 0.921 g / cm) manufactured by Japan Polyethylene Co., Ltd. 3 ) was blended in a mass ratio (recycled material / low-density polyethylene resin) of 40 / 60, and a monolayer film was formed under the extrusion conditions shown below to obtain a monolayer film having a thickness of 50 μm. As a control, a monolayer film having a thickness of 50 μm was obtained similarly using only the low-density polyethylene. The extruder was a single-screw extruder with D (mm) = 20, and a full-flight screw with L / D = 20 and a compression ratio of 3.5 was used. A T-die with a width of 300 mm was used as the die. The thickness of the monolayer film was adjusted by appropriately changing the screw rotation speed and the take-up roll speed. The temperature conditions at this time are shown below. Extrusion temperature: feeding section / compression section / metering section / adapter = 175 / 220 / 220 / 220℃ Die temperature: 220℃ Cooling roll temperature: 80℃ The resulting monolayer film was visually evaluated for coloration and defects and judged according to the following criteria. The results are shown in Table 1. Judging Hue: Standard A: The degree of color change was small compared to the control. B: Slight discoloration was observed compared to the control. C: Moderate coloring was observed compared to the control. D: Significant discoloration was observed compared to the control. E: Compared to the target, significant coloring and unevenness were observed. Judging the product: Criteria A: The amount of pimples was almost the same as the control. B: The amount of small particles was slightly more than in the control. C: Compared to the control, there were more small particles. D: Compared to the control, there was a greater amount of large bumps. E: The amount of large particles was significantly greater than in the control group.

[0086] [Example 2] Resin composition pellets, multilayer films, and multilayer structures were produced in the same manner as in Example 1, except that EVOH-2 (ethylene unit content 24 mol%, saponification degree 99.99 mol%, MFR (210°C, 2.16 kg load) 2.2 g / 10 min, sodium acetate 220 ppm in terms of sodium ions, phosphate ions 30 ppm in terms of phosphate radicals, boric acid 150 ppm in terms of boron element, no polyvalent metal ions) was used instead of EVOH-1, and various measurements and evaluations were performed. The results are shown in Table 1.

[0087] [Example 3] Resin composition pellets, multilayer films, and multilayer structures were produced in the same manner as in Example 1, except that EVOH-3 (ethylene unit content 32 mol%, saponification degree 99.99 mol%, MFR (210°C, 2.16 kg load) 3.7 g / 10 min, sodium acetate 220 ppm in terms of sodium ions, phosphate ions 30 ppm in terms of phosphate radicals, boric acid 150 ppm in terms of boron element, no polyvalent metal ions) was used instead of EVOH-1, and various measurements and evaluations were performed. The results are shown in Table 1.

[0088] [Example 4] Resin composition pellets, multilayer films, and multilayer structures were produced in the same manner as in Example 1, except that EVOH-4 (ethylene unit content 44 mol%, saponification degree 99.99 mol%, MFR (210°C, 2.16 kg load) 3.3 g / 10 min, sodium acetate 250 ppm in terms of sodium ions, phosphate ions 50 ppm in terms of phosphate radicals, boric acid 150 ppm in terms of boron element, no polyvalent metal ions) was used instead of EVOH-1, and various measurements and evaluations were performed. The results are shown in Table 1.

[0089] [Example 5] Resin composition pellets, multilayer films, and multilayer structures were produced in the same manner as in Example 1, except that EVOH-5 (ethylene unit content 48 mol%, saponification degree 99.99 mol%, MFR (210°C, 2.16 kg load) 15 g / 10 min, potassium acetate 150 ppm in potassium ion equivalent, phosphate ion 100 ppm in phosphate radical equivalent, boric acid 200 ppm in boron element equivalent, no polyvalent metal ions) was used instead of EVOH-1, and various measurements and evaluations were performed. The results are shown in Table 1.

[0090] [Example 6] Except for using a mixture (dry blend) of EVOH-2 and EVOH-4 in a weight ratio of 80 / 20 instead of EVOH-1, resin composition pellets, a multilayer film, and a multilayer structure were prepared in the same manner as in Example 1, and various measurements and evaluations were carried out. The results are shown in Table 1.

[0091] [Example 7] Except for using a mixture (dry blend) of EVOH-3 and EVOH-4 in a weight ratio of 90 / 10 instead of EVOH-1, resin composition pellets, a multilayer film, and a multilayer structure were prepared in the same manner as in Example 1, and various measurements and evaluations were carried out. The results are shown in Table 1.

[0092] [Example 8] Resin composition pellets, a multilayer film, and a multilayer structure were prepared in the same manner as in Example 2, except that instead of leaving the pellets in a thermostatic chamber at 40°C and 90% RH for 48 hours, they were left in a thermostatic chamber at 30°C and 70% RH for 12 hours, and various measurements and evaluations were carried out. The results are shown in Table 1.

[0093] [Example 9] Resin composition pellets, a multilayer film, and a multilayer structure were prepared in the same manner as in Example 2, except that instead of leaving the pellets in a thermostatic chamber at 40°C and 90% RH for 48 hours, they were left in a thermostatic chamber at 30°C and 70% RH for 48 hours, and various measurements and evaluations were carried out. The results are shown in Table 1.

[0094] [Example 10] A resin composition pellet, a multilayer film, and a multilayer structure were produced in the same manner as in Example 1, except that an aluminum vapor deposition layer (inorganic vapor deposition layer (I)) having a thickness of 50 nm was laminated on the surface of the barrier layer (A) of the multilayer film obtained in (4) by a known vacuum deposition method, and the inorganic vapor deposition layer and the adhesive layer were laminated together when producing the multilayer structure, and various measurements and evaluations were performed. The results are shown in Table 1.

[0095] [Example 11] Except for changing the 50 nm thick aluminum deposition layer to a 50 nm thick silica (SiOx) deposition layer, resin composition pellets, multilayer films, composite multilayer films, and multilayer structures were produced in the same manner as in Example 10, and various measurements and evaluations were carried out. The results are shown in Table 1.

[0096] [Example 12] Except for changing the 50 nm thick aluminum deposition layer to a 100 nm thick silica (SiOx) deposition layer, resin composition pellets, multilayer films, composite multilayer films, and multilayer structures were produced in the same manner as in Example 10, and various measurements and evaluations were carried out. The results are shown in Table 1.

[0097] [Example 13] Except for changing the 50 nm thick aluminum deposition layer to a 50 nm thick alumina (AlOx) deposition layer, resin composition pellets, multilayer films, composite multilayer films, and multilayer structures were produced in the same manner as in Example 10, and various measurements and evaluations were carried out. The results are shown in Table 2.

[0098] [Examples 14 to 16] Resin composition pellets, multilayer films, and multilayer structures were prepared in the same manner as in Example 1, except that the amount of magnesium stearate kneaded with EVOH-1 was changed as shown in Table 2, and various measurements and evaluations were carried out. The results are shown in Table 2.

[0099] [Examples 17 to 18] Except for changing the magnesium stearate kneaded with EVOH-1 to calcium stearate (Example 17) or zinc stearate (Example 18), resin composition pellets, multilayer films, and multilayer structures were produced in the same manner as in Example 15, and various measurements and evaluations were carried out. The results are shown in Table 2.

[0100] [Examples 19 to 20] Resin composition pellets, multilayer films, and multilayer structures were prepared in the same manner as in Example 1, except that the thicknesses of the barrier layer (A) and the moisture-proof layer (C) were changed as shown in Table 2, and various measurements and evaluations were carried out. The results are shown in Table 2.

[0101] [Example 21] Resin composition pellets, a multilayer film, and a multilayer structure were prepared in the same manner as in Example 1, except that the film was uniaxially stretched 5 times in the machine direction (MD direction) at 100° C. instead of uniaxially stretching 5 times in the machine direction (MD direction) at 115° C., and various measurements and evaluations were carried out. The results are shown in Table 2.

[0102] [Example 22] Resin composition pellets, a multilayer film, and a multilayer structure were prepared in the same manner as in Example 5, except that instead of uniaxially stretching 5 times in the machine direction (MD direction) at 115° C., uniaxially stretching 5 times in the machine direction (MD direction) at 130° C. was performed, and various measurements and evaluations were performed. The results are shown in Table 2.

[0103] [Example 23] Resin composition pellets, multilayer films, and multilayer structures were produced in the same manner as in Example 8, except that the layer structure of the unstretched multilayer film was [outer surface side] moisture-proof layer (C) / adhesive layer (B) / barrier layer (A) [inner surface side]=63 μm / 10.5 μm / 10.5 μm (total thickness 84 μm) and uniaxially stretched 3.5 times in the machine direction (MD direction) at 115° C., and various measurements and evaluations were performed. The results are shown in Table 2.

[0104] [Comparative Example 1] In forming the unstretched multilayer film, only the extruder for the moisture-proof layer (C) was used to adjust the thickness of the moisture-proof layer (C) to 120 μm, and the moisture-proof layer (C) was used instead of the unstretched multilayer film. Except for this, resin composition pellets and a multilayer structure were prepared in the same manner as in Example 1, and various measurements and evaluations were carried out. The results are shown in Table 3.

[0105] [Comparative Example 2] Resin composition pellets and a multilayer structure were produced in the same manner as in Example 10, except that the extruder for the moisture-proof layer (C) was used only when forming the unstretched multilayer film, and the moisture-proof layer (C) having a thickness of 120 μm was obtained, and the moisture-proof layer (C) was used instead of the unstretched multilayer film, and an aluminum vapor-deposited layer (inorganic vapor-deposited layer (I)) having a thickness of 50 nm was laminated on the surface of the stretched moisture-proof layer (C). Various measurements and evaluations were performed. The results are shown in Table 3.

[0106] [Comparative Examples 3 to 4] A resin composition pellet, a multilayer film, and a multilayer structure were prepared in the same manner as in Example 1 and Example 5, except that they were not left to stand in a thermostatic chamber at 40°C and 90% RH for 48 hours, and various measurements and evaluations were carried out for each. The results are shown in Table 3.

[0107] [Comparative Examples 5 to 9] Resin composition pellets, multilayer films, and multilayer structures were prepared in the same manner as in Examples 1 and 2 and Examples 5 to 7, except that instead of leaving the pellets in a thermostatic chamber at 40°C and 90% RH for 48 hours, they were left in a thermostatic chamber at 100°C and 0% RH for 48 hours, and various measurements and evaluations were carried out for each. The results are shown in Table 3.

[0108] [Comparative Examples 10 to 14] Resin composition pellets, multilayer films, and multilayer structures were prepared in the same manner as in Examples 1 and 2 and Examples 5 to 7, except that instead of leaving the pellets in a thermostatic chamber at 40°C and 90% RH for 48 hours, they were left in a thermostatic chamber at 40°C and 0% RH for 48 hours, and various measurements and evaluations were carried out for each. The results are shown in Table 3.

[0109] [Comparative Example 15] Except for changing the stretching temperature to 130° C., resin composition pellets, a multilayer film, and a multilayer structure were produced and various measurements and evaluations were carried out in the same manner as in Comparative Example 4. The results are shown in Table 3.

[0110] [Table 1]

[0111] [Table 2]

[0112] [Table 3]

Claims

1. A multilayer film having a configuration in which a barrier layer (A), an adhesive layer (B), and a moisture-proof layer (C) are laminated in this order, At least one barrier layer (A) is located as the outermost layer of the multilayer film, the barrier layer (A) contains, as a main component, an ethylene-vinyl alcohol copolymer (a) having an ethylene unit content of 20 mol% or more and 50 mol% or less and a saponification degree of 90 mol% or more; The adhesive layer (B) contains, as a main component, an adhesive resin (b) having a melting point of less than 150°C, the moisture-proof layer (C) contains, as a main component, a polyolefin resin (c) having a melting point of less than 150°C; The multilayer film is stretched at least uniaxially by 3 times or more, A multilayer film in which a 10 cm square is cut out from any position of the multilayer film and left to stand in an atmosphere of 20°C and 65% RH for 24 hours, the roll diameter of which is 14 mm or more.

2. 2. The multilayer film according to claim 1, wherein the ethylene-vinyl alcohol copolymer (a) has an ethylene unit content of less than 34 mol%.

3. 2. The multilayer film according to claim 1, wherein the ethylene-vinyl alcohol copolymer (a) comprises an ethylene-vinyl alcohol copolymer (a1) having an ethylene unit content of 22 mol% or more and less than 34 mol% and a degree of saponification of 99 mol% or more, and an ethylene-vinyl alcohol copolymer (a2) having an ethylene unit content of 34 mol% or more and less than 50 mol% and a degree of saponification of 99 mol% or more, and a mass ratio (a1 / a2) of the ethylene-vinyl alcohol copolymer (a1) to the ethylene-vinyl alcohol copolymer (a2) is 80 / 20 to 98 / 2.

4. 2. The multilayer film according to claim 1, wherein the barrier layer (A) contains 10 to 300 ppm of at least one polyvalent metal ion (d) selected from the group consisting of magnesium ions, calcium ions, and zinc ions.

5. 2. The multilayer film according to claim 1, wherein the barrier layer (A) contains 100 to 4,000 ppm of a higher aliphatic carboxylic acid (e) having 8 to 30 carbon atoms.

6. The multilayer film according to claim 1 , wherein the polyolefin resin (c) contains a polyethylene resin as a main component.

7. 2. The multilayer film according to claim 1, wherein the thickness of the barrier layer (A) is 0.2 μm or more and less than 10 μm, and the ratio of the thickness of the barrier layer (A) to the total thickness of all layers of the multilayer film is less than 20%.

8. 2. The multilayer film of claim 1, which is stretched at least three times in the machine direction and is not substantially stretched in the width direction.

9. The multilayer film according to claim 1 , which is an inflation-molded product.

10. A vapor-deposited multilayer film comprising the multilayer film according to claim 1, and an inorganic vapor-deposited layer (I) on the exposed surface side of the barrier layer (A).

11. The oxygen transmission rate measured in accordance with the method described in JIS K 7126-2 (isobaric method; 2006) under the conditions of 20°C and 65% RH is 30 cc / (m ２ The multilayer film or vapor-deposited multilayer film according to any one of claims 1 to 10, wherein the viscosity is less than 1000 kJ / day.

12. A multilayer structure comprising the multilayer film or vapor-deposited multilayer film according to any one of claims 1 to 10 laminated with a resin layer (R) containing a thermoplastic resin (r) as a main component.

13. The multilayer structure according to claim 12, wherein the thermoplastic resin (r) comprises a polyolefin resin having a melting point of less than 150°C as a main component.

14. The multilayer structure according to claim 12, wherein the thermoplastic resin (r) comprises a polyethylene resin as a main component.

15. 13. The multilayer structure according to claim 12, wherein at least one of the moisture proof layer (C) and the resin layer (R) contains a polyethylene resin as a main component, and the ratio of the total thickness of the layers containing a polyethylene resin as a main component to the total thickness of the multilayer structure is 0.75 or more.

16. The multilayer structure according to claim 12, which does not have a layer containing as a main component a resin having a melting point of 240°C or higher and a metal layer having a thickness of 1 µm or more.

17. A packaging material comprising the multilayer structure of claim 12.

18. A method for producing a multilayer film according to any one of claims 1 to 9, A step (I) of producing an unstretched multilayer film having a barrier layer (A), an adhesive layer (B), and a moisture-proof layer (C) in this order; Step (II) of stretching the obtained unstretched multilayer film at least uniaxially to produce a pre-treatment multilayer film; and The method includes a step (III) of treating the stretched untreated multilayer film under conditions of a temperature of 28°C or higher and 60°C or lower and a humidity of 65% RH or higher.

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