Multilayer structure and use thereof

Abstract

A multilayer structure according to the present invention has a layer (X) as an outermost layer, and has a configuration in which at least a layer (X), a layer (Y), and a layer (Z) are laminated adjacent to each other in the stated order. The layer (X) is made of a resin composition (A) containing, as a main component, a modified vinyl alcohol-based polymer (a) having a melting point of 150-175°C. The layer (Y) includes an adhesive resin (B) as a main component. The layer (Z) includes, as a main component, a polyolefin resin (C) having a melting point of 150-175°C. The modified vinyl alcohol-based polymer (a) has a modifying group containing a primary hydroxyl group represented by formula (I). Such a multilayer structure is less likely to tear at end portions even when stretched at high temperatures. Moreover, because the thickness of an outermost layer including the modified vinyl alcohol-based polymer as the main component remains uniform even after stretching, there is good adhesiveness to other layers. Therefore, the multilayer structure is suitable for a variety of uses. (In the formula, one of X and Y is a hydrogen atom, and the other is a hydroxymethyl group or a 2-hydroxyethyl group.)

Description

Multilayer structures and their applications

[0001] This invention relates to a multilayer structure having a modified vinyl alcohol polymer as its outermost layer and its applications.

[0002] Packaging materials for long-term food preservation often require gas barrier properties, including oxygen barrier properties. Using packaging materials with high gas barrier properties can suppress oxidative deterioration of food due to oxygen penetration and the growth of microorganisms. Widely used layers to improve gas barrier properties include metal foils such as aluminum, and inorganic vapor-deposited layers such as silicon dioxide and aluminum oxide. On the other hand, resin layers with gas barrier properties, such as vinyl alcohol polymers and polyvinylidene chloride, are also widely used. Vinyl alcohol polymers exhibit gas barrier properties through crystallization and densification caused by hydrogen bonding between hydroxyl groups in the molecule. Among these, ethylene-vinyl alcohol copolymers (hereinafter sometimes abbreviated as "EVOH") are suitable for melt molding due to their excellent thermal stability, and with the development of co-extrusion technology, multilayer films containing EVOH layers are widely used as gas barrier packaging materials.

[0003] Furthermore, in recent years, driven by environmental and waste issues, there has been a growing global demand for so-called post-consumer recycling (hereinafter sometimes simply referred to as recycling), which involves collecting and recycling packaging materials consumed in the market. For these reasons, there is an increasing demand for diversification of layer configurations and synergistic effects of improved barrier properties through lamination with inorganic vapor-deposited layers, leading to the increasing use of EVOH layers as the outermost layer of multilayer films (Patent Documents 1 and 2).

[0004] Japanese Patent Publication No. 2021-24266, International Publication No. 2021 / 261560

[0005] However, in multilayer films where the EVOH layer is the outermost layer (Patent Documents 1 and 2), thickness variations occur in the EVOH layer during stretching, resulting in insufficient adhesion to adjacent layers, and tearing may occur at the edges when tenter stretching at high temperatures. The present invention was made to solve the above problems and aims to provide a multilayer structure with good stretchability and good adhesion to adjacent layers.

[0006] As a result of diligent research to solve the above problems, the present inventors have found that by using a modified vinyl alcohol polymer for the outermost layer, which has a melting point within a predetermined range and a modified group containing a predetermined primary hydroxyl group, a multilayer structure with good stretchability and good adhesion to adjacent layers can be obtained.

[0007] In other words, the present invention is as follows: [1] A multilayer structure having layer (X) as the outermost layer, with at least layers (X), (Y), and (Z) stacked adjacently in this order, wherein layer (X) is made of a resin composition (A) mainly composed of a modified vinyl alcohol polymer (a) with a melting point of 150°C or more and 175°C or less, layer (Y) mainly composed of an adhesive resin (B), layer (Z) mainly composed of a polyolefin resin (C) with a melting point of 150°C or more and 175°C or less, and the modified vinyl alcohol polymer (a) has a modified group containing a primary hydroxyl group represented by the following formula (I).

[0008]

[0009] [In the formula, one of X and Y is a hydrogen atom, and the other is a hydroxymethyl group or a 2-hydroxyethyl group.] [2] The multilayer structure according to [1], wherein the resin composition (A) contains 90% by mass or more of the modified vinyl alcohol polymer (a). [3] Resin composition (A) at a temperature of 210°C and a shear rate of 12 sec. －１ melt viscosity η １２ A multilayer structure according to [1] or [2], wherein the shear rate is 2,000 Pa·s or less. [4] Temperature of resin composition (A) 210°C, shear rate 120 sec －１ melt viscosity η １２０ The melt viscosity η １２ The ratio of (η １２ / η １２０[1] to [3] any one of the multilayer structures, wherein the boron compound content of the resin composition (A) is 1.5 or less. [5] The multilayer structure according to any one of the items [1] to [4], wherein the boron compound content of the resin composition (A) is less than 30 ppm in terms of boron elements. [6] The multilayer structure according to any one of the items [1] to [5], which is stretched at least twice in one axial direction. [7] The multilayer structure according to any one of the items [1] to [6], wherein the modified vinyl alcohol polymer (a) is a modified ethylene-vinyl alcohol copolymer having an ethylene unit content of 15 to 85 mol%. [8] The multilayer structure according to any one of the items [1] to [7], wherein X in formula (I) is a hydroxymethyl group or a 2-hydroxyethyl group and Y is a hydrogen atom. [9] An extruded product comprising the multilayer structure according to any one of the items [1] to [8].

[10] A vapor-deposited multilayer film having an inorganic vapor-deposited layer on the exposed surface side of layer (X) of the extruded product according to [9].

[11] A heat-shrinkable film or heat-shrinkable sheet made of a multilayer structure as described in any one of items [1] to [8].

[12] A co-extruded blow-molded container made of a multilayer structure as described in any one of items [1] to [8].

[13] A thermoformed article made of a multilayer structure as described in any one of items [1] to [8].

[14] A fuel container made of a multilayer structure as described in any one of items [1] to [8].

[0010] The multilayer structure of the present invention is less prone to tearing at the edges even when stretched at high temperatures. Moreover, since the thickness of the outermost layer, which is mainly composed of a modified vinyl alcohol polymer, remains uniform even after stretching, it exhibits good adhesion to other layers. Therefore, this multilayer structure is suitable for a variety of applications.

[0011] The multilayer structure of the present invention has a layer (X) as the outermost layer, and at least layers (X), (Y), and (Z) are laminated adjacently in this order, wherein layer (X) is made of a resin composition (A) mainly composed of a modified vinyl alcohol polymer (a) with a melting point of 150°C to 175°C, layer (Y) mainly composed of an adhesive resin (B), and layer (Z) mainly composed of a polyolefin resin (C) with a melting point of 150°C to 175°C, and the modified vinyl alcohol polymer (a) has a modified group containing a primary hydroxyl group represented by the following formula (I). Here, "layers (X), (Y), and (Z) are laminated adjacently in this order" means that adjacent layers are directly laminated, specifically that layers (X), (Y), and (Z) are laminated in this order, with layer (X) and layer (Y) directly laminated, and layer (Y) and layer (Z) directly laminated. Furthermore, in this invention, "main component" means a component that is contained in an amount exceeding 50% by mass. Because the multilayer structure has good stretchability, it is less likely to tear at the edges even when stretched at high temperatures, and even after stretching, the thickness of the outermost layer, which is mainly composed of a modified vinyl alcohol polymer (X), is uniform, resulting in good adhesion to layer (Y).

[0012]

[0013] [In the formula, one of X and Y is a hydrogen atom, and the other is a hydroxymethyl group or a 2-hydroxyethyl group.]

[0014] <Resin Composition (A)> The multilayer structure of the present invention has a layer (X) on its outermost surface made of a resin composition (A) mainly composed of a modified vinyl alcohol polymer (a) having a melting point of 150°C or higher and 175°C or lower. In addition to the above components, the resin composition (A) may also contain a vinyl alcohol polymer other than the modified vinyl alcohol polymer (a) (e); alkali metal ions (b); at least one polyvalent metal ion selected from the group consisting of magnesium ions, calcium ions, and zinc ions (c); a higher aliphatic carboxylic acid having 8 to 30 carbon atoms (d); and other components described later. A detailed explanation follows below.

[0015] <Modified vinyl alcohol polymer (a)> When the melting point of the modified vinyl alcohol polymer (a) is 150°C or higher and 175°C or lower, the stretchability of the multilayer structure having a layer (X) mainly composed of the modified vinyl alcohol polymer (a) as the outermost layer is improved. Specifically, even when stretched at high temperatures, tearing is less likely to occur at the edges of the multilayer structure, and the thickness of the outermost layer (X) remains uniform after stretching. Thus, the uniform thickness of the layer (X) after stretching results in good adhesion between layer (X) and layer (Y). If the melting point of the modified vinyl alcohol polymer (a) is less than 150°C, the thickness of the layer (X) after stretching becomes uneven. As a result, the adhesion between the thin part of layer (X) and the adjacent layer (Y) is significantly reduced. The melting point is preferably 153°C or higher, more preferably 155°C or higher, even more preferably 157°C or higher, and particularly preferably 158°C or higher. On the other hand, if the melting point of the modified vinyl alcohol polymer (a) exceeds 175°C, the adhesion to layer (Y) decreases regardless of the thickness of layer (X). The melting point of the modified vinyl alcohol polymer (a) is preferably 172°C or lower, more preferably 168°C or lower, even more preferably 165°C or lower, even more preferably 163°C or lower, and particularly preferably 162°C or lower. The melting point of the modified vinyl alcohol polymer (a) is controlled by one or more of the following: (1) Introducing ethylene units and changing the ethylene unit content (increasing the ethylene unit content lowers the melting point) (2) Changing the degree of saponification (decreasing the degree of saponification lowers the melting point) (3) Changing the content of modified groups containing primary hydroxyl groups (increasing the content of modified groups containing primary hydroxyl groups lowers the melting point)

[0016] The modified vinyl alcohol-based polymer (a) has a modifying group containing a primary hydroxyl group represented by the above formula (I). As a result, the multilayer structure can be stretched at a high magnification, and the adhesiveness between the layer (X) and the layer (Y) is improved. The content of the modifying group in the modified vinyl alcohol-based polymer (a) is preferably 0.1 to 3 mol%. The content of the modifying group is more preferably 0.3 mol% or more, further preferably 0.7 mol% or more, and particularly preferably 1.2 mol% or more. On the other hand, the content of the modifying group is more preferably 2.7 mol% or less, further preferably 2.3 mol% or less, even more preferably 2 mol% or less, and particularly preferably 1.7 mol% or less. In the modified vinyl alcohol-based polymer (a), the contents of the modifying group, ethylene unit, and vinyl alcohol unit, as well as the saponification degree, are determined by NMR measurement.

[0017] In the above formula (I), one of X and Y is a hydrogen atom, and the other is a hydroxymethyl group or a 2-hydroxyethyl group. From the viewpoint of further improving the stretchability and adhesiveness of the multilayer structure, it is preferable that X is a hydroxymethyl group or a 2-hydroxyethyl group and Y is a hydrogen atom, and it is more preferable that X is a hydroxymethyl group and Y is a hydrogen atom.

[0018] It is also preferable that the modified vinyl alcohol polymer (a) contains ethylene units, that is, that the modified vinyl alcohol polymer (a) is a modified ethylene-vinyl alcohol polymer. This improves the water resistance, thermal stability, melt moldability, and secondary processability of the multilayer structure. When the modified vinyl alcohol polymer (a) contains ethylene units, the ethylene unit content is preferably 15 mol% or more, more preferably 20 mol% or more, even more preferably 25 mol% or more, even more preferably 30 mol% or more, and particularly preferably 34 mol% or more. On the other hand, if the ethylene unit content of the modified vinyl alcohol polymer (a) is too high, the gas barrier properties may be insufficient, and the adhesion to the layer (Y) and the inorganic vapor deposition layer described later may decrease. From this viewpoint, the ethylene unit content of the modified vinyl alcohol polymer (a) is preferably 85 mol% or less, more preferably 65 mol% or less, even more preferably 50 mol% or less, even more preferably 46 mol% or less, particularly preferably 42 mol% or less, and most preferably 40 mol% or less. The modified vinyl alcohol polymer (a) may consist of two or more vinyl alcohol polymers with different ethylene unit content. The ethylene unit content can be controlled by various methods, but it can be controlled by the ethylene pressure applied in the polymerization process, the ratio of vinyl ester to solvent, etc.

[0019] To improve gas barrier properties, the vinyl alcohol unit content of the modified vinyl alcohol polymer (a) is preferably 15 mol% or more, more preferably 30 mol% or more, even more preferably 40 mol% or more, and may be 50 mol% or more. The vinyl alcohol unit content of the modified vinyl alcohol polymer (a) is preferably 85 mol% or less, more preferably 80 mol% or less, and particularly preferably 75 mol% or less.

[0020] The degree of saponification of the modified vinyl alcohol polymer (a) is preferably 60 mol% or higher. If the degree of saponification is less than 60 mol%, the gas barrier properties and thermal stability will be insufficient, and the interlayer adhesion with the layer (Y) and inorganic vapor deposition layer described later may decrease. A degree of saponification of 70 mol% or higher is more preferable, and 80 mol% or higher is even more preferable. The upper limit of the degree of saponification is 100 mol%, but from the viewpoint of material balance and energy balance in the production process, a degree of saponification of 99.99 mol% or lower is preferable. Here, the degree of saponification means the ratio of the number of alcohol units to the total number of alcohol units and ester units in the modified vinyl alcohol polymer (a). The modified vinyl alcohol polymer (a) may consist of two or more vinyl alcohol polymers with different degrees of saponification. The degree of saponification can be controlled by various methods, but it can be controlled by the amount of alkali catalyst, water content, reaction temperature and reaction time in the saponification process. Furthermore, the hydroxyl groups generated in the saponification process can also be controlled by esterifying them with a carboxylic acid such as acetic acid or its anhydride in a process that follows saponification.

[0021] The melt flow rate (MFR) (at 190 °C under a load of 2160 g) of the resin composition (A) measured according to the method described in JIS K7210 (2014) is preferably 0.5 to 30 g / 10 min. The MFR is more preferably 1 g / 10 min or more, still more preferably 2 g / 10 min or more, and particularly preferably 4 g / 10 min or more. When the MFR is at least the above lower limit value, even when the preheating time and heat fixing time are short in the stretching step, the adhesiveness between the layer (X) and the layer (Y) tends to be excellent, which is preferable from the viewpoint of achieving both a high production speed and a high interlayer adhesive strength. This is presumably because when the MFR is at least the above lower limit value, even when the preheating time and heat fixing time are short, the primary hydroxyl group of the modified vinyl alcohol-based polymer (a) and the adhesive functional group of the adhesive resin (B) (when the adhesive resin (B) is a carboxylic acid-modified polyolefin resin, the carboxyl group) easily react. On the other hand, the MFR is more preferably 20 g / 10 min or less, still more preferably 15 g / 10 min or less, and particularly preferably 10 g / 10 min or less. When the MFR is at most the above upper limit value, the thickness unevenness of the layer (X) becomes small, and the interlayer adhesive strength and gas barrier property of the film after stretching are likely to be stabilized.

[0022] From the viewpoint of preventing film surface roughness when manufacturing the multilayer structure by the coextrusion molding method, the melt viscosity η of the resin composition (A) at a temperature of 210 °C and a shear rate of 12 sec －１ is preferably 2,000 Pa·s or less. The melt viscosity η １２ is more preferably 1,500 Pa·s or less, still more preferably 1,200 Pa·s or less, and particularly preferably 1,100 Pa·s or less. On the other hand, from the viewpoint of thickness stability when manufacturing the multilayer structure by the coextrusion molding method, the melt viscosity η １２ is preferably 600 Pa·s or more, and may be more preferably 750 Pa·s or more, 850 Pa·s or more, or 900 Pa·s or more in some cases. The melt viscosity η １２ is measured by the method described in the examples below. １２ is measured by the method described in the examples described below.

[0023] From the viewpoint of preventing surface roughness of the film when manufacturing the multilayer structure by co-extrusion molding, the temperature of the resin composition (A) is 210°C and the shear rate is 120 sec. －１ melt viscosity η １２０ It is preferable that the melt viscosity is 1,300 Pa·s or less. １２０ It is more preferably 1,200 Pa·s or less, even more preferably 1,000 Pa·s or less, and particularly preferably 800 Pa·s or less. On the other hand, from the viewpoint of stabilizing the thickness when manufacturing the multilayer structure by co-extrusion molding, the melt viscosity η １２０ The melt viscosity η is preferably 500 Pa·s or higher, and may be more preferably 550 Pa·s or higher or 650 Pa·s or higher. １２０ This is measured by the method described in the examples below.

[0024] From the viewpoint of suppressing defects when manufacturing the multilayer structure by co-extrusion molding, the melt viscosity η １２０ The melt viscosity η １２ The ratio of (η １２ / η １２０ It is also preferable that the ratio (η) is 1.6 or less. From the viewpoint of preventing surface roughness of the film when manufacturing the multilayer structure by co-extrusion molding, and from the viewpoint of suppressing thickness unevenness after stretching, the ratio (η) is preferable. １２ / η １２０ ) is more preferably 1.5 or less, and even more preferably 1.4 or less. On the other hand, the ratio (η １２ / η １２０ The ratio (η) is usually 1.2 or higher. １２ / η １２０ The fact that the above range is present allows for the acquisition of a multilayer structure with fewer imperfections over a wide film-forming temperature range, which helps prevent film tearing during biaxial stretching caused by imperfections.

[0025] Modified vinyl alcohol polymers (a) can usually be obtained by saponifying a modified vinyl ester polymer obtained by copolymerizing a vinyl ester, a monomer represented by the following formula (II), and optionally ethylene or other monomers. The production and saponification of vinyl ester polymers can be carried out by known methods. R in the following formulas (II) and (III) １and R ２ It is preferable that this is a methyl group. The ester group in the unit derived from the monomer represented by the following formula (II) contained in the modified vinyl ester polymer obtained by copolymerization is hydrolyzed during saponification to form a modified group represented by the above formula (I).

[0026] [In the formula, one of X' and Y' is a hydrogen atom, and the other is a group represented by the following formula (III). R １ This is a hydrogen atom or an alkyl group having 1 to 9 carbon atoms.

[0027] [In the formula, R ２ n is a hydrogen atom or an alkyl group having 1 to 9 carbon atoms. n is 1 or 2.

[0028] The modified vinyl alcohol polymer (a) may contain other monomer units other than the ethylene unit, vinyl ester unit, vinyl alcohol unit, and the modified group containing the primary hydroxyl group represented by formula (I) above, as long as they do not impair the effects of the present disclosure. The content of other monomer units is preferably 5 mol% or less, more preferably 3 mol% or less, even more preferably 1 mol% or less, and particularly preferably substantially absent. Other such monomers include, for example, α-olefins such as propylene, n-butene, isobutylene, and 1-hexene; acrylic acid and its salts; unsaturated monomers having an acrylic acid ester group; methacrylic acid and its salts; unsaturated monomers having a methacrylic acid ester group; acrylamide, N-methylacrylamide, N-ethylacrylamide, N,N-dimethylacrylamide, diacetoneacrylamide, acrylamidepropanesulfonic acid and its salts, acrylamidepropyldimethylamine and its salts (e.g., quaternary salts); methacrylamide, N-methylmethacrylamide, N-ethylmethacrylamide, methacrylamidepropanesulfonic acid and its salts, methacrylamidepropyldimethylamine and its salts (e.g., quaternary salts); methyl vinyl ether, etc. Examples include vinyl ethers such as butyl vinyl ether, n-propyl vinyl ether, i-propyl vinyl ether, n-butyl vinyl ether, i-butyl vinyl ether, t-butyl vinyl ether, dodecyl vinyl ether, stearyl vinyl ether, and 2,3-diacetoxy-1-vinyloxypropane; vinyl cyanides such as acrylonitrile and methacrylonitrile; vinyl halides such as vinyl chloride and vinyl fluoride; vinylidenes such as vinylidene chloride and vinylidene fluoride; allyl compounds such as allyl acetate, 2,3-diacetoxy-1-allyloxypropane, and allyl chloride; unsaturated dicarboxylic acids such as maleic acid, itaconic acid, and fumaric acid, and their salts or esters; vinylsilane compounds such as vinyltrimethoxysilane; and isopropenyl acetate.

[0029] <Vinyl alcohol polymer (e)> The resin composition (A) may contain less than 50% by mass of a vinyl alcohol polymer (e) other than the modified vinyl alcohol polymer (a). Examples of vinyl alcohol polymer (e) include vinyl alcohol polymer (e1) with a melting point of less than 150°C or greater than 175°C; and vinyl alcohol polymer (e2) with a melting point of 150°C or more and 175°C or less, which does not have a modified group containing a primary hydroxyl group represented by formula (I). For vinyl alcohol polymer (e1), the description for modified vinyl alcohol polymer (a) can be applied as is, except that the melting point is less than 150°C or greater than 175°C, and that it may or may not have a modified group containing a primary hydroxyl group represented by formula (I). For vinyl alcohol polymer (e2), the description for modified vinyl alcohol polymer (a) can be applied as is, except that it does not have a modified group containing a primary hydroxyl group represented by formula (I). From the viewpoint of cost reduction, the content of vinyl alcohol polymer (e) is preferably 5% by mass or more, more preferably 20% by mass or more, and even more preferably 35% by mass or more. On the other hand, from the viewpoint of more significantly exhibiting the effects of the present invention, the lower the content of vinyl alcohol polymer (e), the better, less than 50% by mass is preferable, but substantially none is preferable. As vinyl alcohol polymer (e), various brands of "EVAL® resin" manufactured by Kuraray Co., Ltd. can be preferably used.

[0030] <Alkali metal ions (b)> The resin composition (A) may contain alkali metal ions (b) in an amount of 25 to 1500 ppm. By including alkali metal ions (b) in the resin composition (A) within the above range, the interlayer adhesion between layer (X) and layer (Y), described later, is further improved. The alkali metal ion (b) content is more preferably 50 ppm or more, even more preferably 70 ppm or more, and particularly preferably 90 ppm or more. On the other hand, if the alkali metal ions (b) content exceeds 1500 ppm, the resin composition (A) may decompose excessively during melt molding, or discoloration may become a problem. The alkali metal ion (b) content is more preferably 1000 ppm or less, even more preferably 750 ppm or less, and particularly preferably 500 ppm or less. In this specification, "ppm" means "mass ppm".

[0031] Examples of alkali metal ions (b) include lithium, sodium, potassium, rubidium, and cesium ions, but sodium or potassium ions are preferred from the standpoint of industrial availability. These may be used individually or in combination of two or more.

[0032] Examples of alkali metal compounds that provide alkali metal ions (b) 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 due to their ease of availability and handling. Among aliphatic carboxylates, acetates, caprylates, and stearates are preferred.

[0033] <Polyvalent metal ions (c)> The resin composition (A) may contain 10 to 300 ppm of at least one polyvalent metal ion (c) selected from the group consisting of magnesium ions, calcium ions, and zinc ions. When the polyvalent metal ion (c) is contained in an amount of 10 ppm or more, it tends to suppress appearance defects such as thickening and the generation of gel or lumps during the melt molding of the resin composition (A). On the other hand, when the polyvalent metal ion (c) content is 300 ppm or less, it tends to suppress excessive decomposition and discoloration during the melt molding of the resin composition (A). Furthermore, when recycling the multilayer structure of the present invention, crosslinking reactions of the resin may progress during the melt molding of the pulverized multilayer structure, causing thickening and gelation. However, by containing a certain amount of polyvalent metal ion (c), thickening, gelation, and adhesion of the resin to the screw are suppressed. From this viewpoint, the polyvalent metal ion (c) content is more preferably 20 to 260 ppm, and even more preferably 30 to 220 ppm. In particular, the resin composition (A) preferably contains magnesium ions or calcium ions as polyvalent metal ions (c), and more preferably contains calcium ions.

[0034] Examples of polyvalent metal compounds that yield polyvalent metal ions (c) 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 due to their ease of availability and handling. Among aliphatic carboxylates, acetates, caprylates, and stearates are preferred.

[0035] <Higher Aliphatic Carboxylic Acid (d)> The resin composition (A) may contain 100 to 4000 ppm of a higher aliphatic carboxylic acid (d) having 8 to 30 carbon atoms. The higher aliphatic carboxylic acid (d) may be contained in part or all in the form of a salt, or it may be contained as a salt of an alkali metal ion (b) or a polyvalent metal ion (c). Caprylic acid or stearic acid is preferred as the higher aliphatic carboxylic acid (d). The multilayer structure of the present invention has a layer (X) made of the resin composition (A) as the outermost layer, and it is thought that the higher aliphatic carboxylic acid (d) acts as a lubricant with the die metal surface inside the die, thereby suppressing appearance defects caused by uneven thickness of the multilayer film and the generation of gels and lumps due to retained resin. For this reason, it is preferable that the resin composition (A) contains 100 ppm or more of the higher aliphatic carboxylic acid (d). On the other hand, when the content of higher aliphatic carboxylic acid (d) is 4000 ppm or less, it tends to suppress thickening during melt molding of the resin composition (A) and maintain interlayer adhesion with the layer (Y) described later. From these viewpoints, the content of higher aliphatic carboxylic acid (d) is more preferably 200 to 3000 ppm, and even more preferably 300 to 2500 ppm.

[0036] Resin composition (A) may contain other components besides modified vinyl alcohol polymer (a), vinyl alcohol polymer (e), alkali metal ions (b), polyvalent metal ions (c), and higher aliphatic carboxylic acids (d), as long as the effects of the present invention are not hindered. Examples of other components include alkaline earth metal ions and transition metal ions other than polyvalent metal ions (c), carboxylic acids other than higher aliphatic carboxylic acids (d) (monocarboxylic acids, polyvalent carboxylic acids), thermoplastic resins other than modified vinyl alcohol polymer (a) and vinyl alcohol polymer (e), phosphoric acid compounds, boron compounds, oxidation accelerators, antioxidants (hindered phenol compounds, etc.), plasticizers, heat stabilizers (melt stabilizers), photoinitiators, deodorizers, ultraviolet absorbers, antistatic agents, lubricants, colorants, fillers, desiccants, fillers, pigments, dyes, processing aids, flame retardants, antifogging agents, etc. From the viewpoint of suppressing discoloration when melt-molding pulverized multilayer structures containing resin composition (A), it is preferable to include carboxylic acids and / or phosphoric acid compounds. Furthermore, by including a boron compound, the melt viscosity of the resin composition (A) and the pulverized multilayer structure containing the resin composition (A) can be controlled.

[0037] <Carboxylic Acids> The resin composition (A) preferably contains carboxylic acids other than the higher aliphatic carboxylic acid (d). The lower limit of the carboxylic acid content is preferably 50 ppm, and more preferably 100 ppm. On the other hand, the upper limit of the carboxylic acid content is preferably 400 ppm, and more preferably 350 ppm. When the carboxylic acid content is 50 ppm or more, the color 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 odor can be suppressed.

[0038] The pKa of the carboxylic acid is preferably 3.5 to 5.5. When the pKa of the carboxylic acid is within this range, the pH buffering capacity of the resulting resin composition (A) is increased, further improving melt moldability and reducing discoloration by acidic and basic substances.

[0039] The carboxylic acid may be a monovalent carboxylic acid. These may be used individually or in combination of two or more. A monovalent carboxylic acid is a compound having one carboxyl group in its molecule. Monovalent carboxylic acids with a pKa in the range of 3.5 to 5.5 are not particularly limited and include, for example, formic acid (pKa = 3.77), acetic acid (pKa = 4.76), propionic acid (pKa = 4.85), and acrylic acid (pKa = 4.25). These carboxylic acids may further have substituents such as hydroxyl groups, amino groups, and halogen atoms. Among these, acetic acid is preferred because of its high safety and ease of availability and handling.

[0040] The carboxylic acid may be a polycarboxylic acid. If the carboxylic acid is a polycarboxylic acid, the color resistance of the resin composition (A) at high temperatures and the color resistance of the melt-molded product of the crushed multilayer structure obtained may be further improved. Furthermore, it is preferable that the polycarboxylic acid compound has three or more carboxyl groups. In this case, the color resistance may be improved more effectively. A polycarboxylic acid is a compound having two or more carboxyl groups in its molecule. In this case, it is preferable that the pKa of at least one carboxyl group is in the range of 3.5 to 5.5, for example, oxalic acid (pKa2 = 4.27), succinic acid (pKa1 = 4.20), fumaric acid (pKa2 = 4.44), malic acid (pKa2 = 5.13), glutaric acid (pKa1 = 4.30, pKa2 = 5.40), adipic acid (pKa1 = 4.43, pKa Examples include pKa2 = 5.41, pKa2 = 4.71, pKa2 = 5.41, pKa2 = 4.46, pKa2 = 4.82, pKa2 = 3.51, pKa2 = 4.75, pKa2 = 4.40, pKa2 = 4.07, pKa2 = 4.07, and pKa2 = 3.90.

[0041] <Phosphate Compounds> The resin composition (A) may further contain phosphate compounds. The lower limit of the phosphate compound content is preferably 5 ppm in terms of phosphate root. On the other hand, the upper limit of the phosphate compound content is preferably 100 ppm in terms of phosphate root. By including phosphate compounds within this range, discoloration of the resulting resin composition (A) and the melt-molded product of the pulverized multilayer structure may be suppressed, and the thermal stability may be improved.

[0042] As phosphate compounds, various acids such as phosphoric acid and phosphorous acid, and their salts can be used. The phosphate may be any of the first, second, or third phosphates. The cation species of the phosphate is not particularly limited, but alkali metals and alkaline earth metals are preferred. Among these, sodium dihydrogen phosphate, potassium dihydrogen phosphate, disodium hydrogen phosphate, and dipotassium hydrogen phosphate are preferred as phosphate compounds.

[0043] <Boron Compounds> From the viewpoint of preventing surface roughness of the film when manufacturing the multilayer structure by co-extrusion molding, the content of boron compounds in resin composition (A) may be 100 ppm or less in terms of boron element, preferably 50 ppm or less, and more preferably 30 ppm or less. From the above viewpoint, the content of boron compounds in resin composition (A) may preferably be 25 ppm or less, 20 ppm or less, 15 ppm or less, or 10 ppm or less in terms of boron element, or it may be preferable that resin composition (A) does not contain boron compounds. The content of boron compounds in resin composition (A) may be 0 ppm in terms of boron element, and it may be preferable that it be 0.1 ppm or more or 1 ppm or more. By including boron compounds within this range, the thermal stability of the resin composition (A) and the pulverized material of the resulting multilayer structure during melt molding is improved, and the generation of gel and lumps may be suppressed. Furthermore, the resistance to drawdown and neck-in during film formation may be improved, and the mechanical properties of the resulting molded article may be enhanced. These effects are presumed to be due to chelate interactions occurring between the modified vinyl alcohol polymer (a) and the boron compound.

[0044] Examples of boron compounds include boric acid, boric acid esters, borates, and boron hydride. Specifically, orthoboric acid (H ３ BO ３ Examples include boric acid such as metaboric acid and tetraboric acid; boric acid esters such as trimethyl borate and triethyl borate; alkali metal salts or alkaline earth metal salts of the aforementioned boric acid, and borates such as borax. Among these, orthoboric acid is preferred.

[0045] <Hindered phenol compounds> The resin composition (A) may further contain hindered phenol compounds. When hindered phenol compounds are included, the content of hindered phenol compounds in the resin composition (A) is preferably 1,000 to 10,000 ppm. When the content is 1,000 ppm or more, discoloration, thickening, and gelation of the resin can be suppressed when melt-molding the pulverized multilayer structure. A content of 2,000 ppm or more of hindered phenol compounds is more preferable. On the other hand, when the content of hindered phenol compounds is 10,000 ppm or less, discoloration and bleed-out originating from the hindered phenol compounds can be suppressed. A content of 8,000 ppm or less of hindered phenol compounds is more preferable.

[0046] Hindered phenol compounds have at least one hindered phenol group. A hindered phenol group is defined as a group in which a bulky substituent is bonded to at least one carbon adjacent to the carbon atom to which the hydroxyl group of phenol is bonded. The bulky substituent is preferably an alkyl group with 1 to 10 carbon atoms, and more preferably a t-butyl group.

[0047] The hindered phenol compound is preferably in a solid state at or near room temperature. From the viewpoint of suppressing bleed-out of the compound, the melting point or softening temperature of the hindered phenol compound is preferably 50°C or higher, more preferably 60°C or higher, and even more preferably 70°C or higher. From the same viewpoint, the molecular weight of the hindered phenol compound is preferably 200 or higher, more preferably 400 or higher, and even more preferably 600 or higher. On the other hand, the molecular weight is usually 2000 or lower. Furthermore, from the viewpoint of facilitating mixing with the modified vinyl alcohol polymer (a), the melting point or softening temperature of the hindered phenol compound is preferably 200°C or lower, more preferably 190°C or lower, and even more preferably 180°C or lower.

[0048] Hindered phenol compounds preferably have an ester bond or an amide bond. Examples of hindered phenol compounds having an ester bond include esters of an aliphatic carboxylic acid having a hindered phenol group and an aliphatic alcohol, and examples of hindered phenol compounds having an amide include amides of an aliphatic carboxylic acid having a hindered phenol group and an aliphatic amine. Among these, it is preferable that the hindered phenol compound has an amide bond.

[0049] Specific structures of hindered phenol compounds having ester or amide bonds include pentaerythritol tetrakis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], which is commercially available from BASF as Irganox 1010; stearyl 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, which is commercially available as Irganox 1076; 2,2'-thiodiethylbis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], which is commercially available as Irganox 1035; and Irganox 1135. Examples of commercially available products include octadecyl 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propanoate, bis(3-tert-butyl-4-hydroxy-5-methylbenzenepropanoate)ethylenebis(oxyethylene) sold as Irganox 245, 1,6-hexanediol bis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] sold as Irganox 259, and N,N'-hexamethylenebis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propanamide] sold as Irganox 1098. In particular, N,N'-hexamethylenebis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propanamide], which is commercially available as Irganox 1098, and pentaerythritol tetrakiss[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], which is commercially available as Irganox 1010, are preferred, with the former being more preferred.

[0050] The resin composition (A) may further contain other thermoplastic resins other than the modified vinyl alcohol polymer (a) and the vinyl alcohol polymer (e). Examples of other thermoplastic resins other than the modified vinyl alcohol polymer (a) and the vinyl alcohol polymer (e) include various polyolefins (polyethylene, polypropylene, poly-1-butene, poly-4-methyl-1-pentene, ethylene-propylene copolymer, copolymer of ethylene and α-olefin having 4 or more carbon atoms, copolymer of polyolefin and maleic anhydride, ethylene-vinyl ester copolymer, ethylene-acrylic acid ester copolymer, or modified polyolefins obtained by grafting these with unsaturated carboxylic acids or their derivatives), various polyamides (nylon 6, nylon 6・6, nylon 6 / 66 copolymer, 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, and polyacrylate. The content of the other thermoplastic resin in the resin composition (A) is usually 40% by mass or less, preferably 30% by mass or less, more preferably 20% by mass or less, even more preferably 10% by mass or less, and may be 5% by mass or less, or even 1% by mass or less, and it is particularly preferable that it be substantially absent.

[0051] From the viewpoint of more significantly demonstrating the effects of the present invention, the proportion of the modified vinyl alcohol polymer (a) in the resin constituting the resin composition (A) is preferably 60% by mass or more, more preferably 70% by mass or more, even more preferably 80% by mass or more, even more preferably 90% by mass or more, and particularly preferably 95% by mass or more. The resin constituting the resin composition (A) may consist substantially only of the modified vinyl alcohol polymer (a). Furthermore, from the viewpoint of more significantly demonstrating the effects of the present invention, the proportion of the modified vinyl alcohol polymer (a) in the resin composition (A) is preferably 60% by mass or more, more preferably 70% by mass or more, even more preferably 80% by mass or more, even more preferably 90% by mass or more, particularly preferably 95% by mass or more, and most preferably 98% by mass or more.

[0052] Furthermore, from the viewpoint of achieving good gas barrier properties at low cost, the total content of modified vinyl alcohol polymer (a) and vinyl alcohol polymer (e) in the resin constituting the resin composition (A) is preferably 70% by mass or more, more preferably 90% by mass or more, even more preferably 95% by mass or more, and particularly preferably 99% by mass or more. The resin constituting the resin composition (A) may consist substantially only of modified vinyl alcohol polymer (a) and vinyl alcohol polymer (e).

[0053] Furthermore, from the viewpoint of achieving good gas barrier properties at low cost, the total content of modified vinyl alcohol polymer (a) and vinyl alcohol polymer (e) in the resin composition (A) is preferably 70% by mass or more, more preferably 90% by mass or more, even more preferably 95% by mass or more, and particularly preferably 99% by mass or more.

[0054] The method for producing the resin composition (A) is not particularly limited, but it can be produced by melt-kneading a modified vinyl alcohol polymer (a), and optionally other components such as a vinyl alcohol polymer (e), alkali metal ions (b), polyvalent metal ions (c), or higher aliphatic carboxylic acids (d). Each component may be blended in a solid state such as powder, or as a melt, or as a solute in a solution or a dispersed in a dispersion. Aqueous solutions and aqueous dispersions are preferred as the solution and dispersion, respectively. For melt-kneading, known mixing or kneading equipment such as a kneader-ruder, extruder, mixing roll, or Banbury mixer can be used. The temperature range during melt-kneading can be appropriately adjusted according to the modified vinyl alcohol polymer (a) used and the melting points of each component, and is usually 150 to 250°C. Alternatively, some components may be added to the modified vinyl alcohol polymer (a) in advance, and then other necessary components may be melt-kneaded as described above. One example of a method for pre-adding several components to the modified vinyl alcohol polymer (a) is to immerse the modified vinyl alcohol polymer (a) as pellets or powder in a solution in which the added components are dissolved. An aqueous solution is preferred as the solution.

[0055] <Adhesive Resin (B)> The multilayer film of the present invention has a layer (Y) mainly composed of adhesive resin (B). The inclusion of layer (Y) in the multilayer film of the present invention tends to result in a multilayer film with excellent appearance and interlayer adhesion. Examples of adhesive resin (B) include carboxylic acid-modified polyolefin resins obtained by graft polymerization of an unsaturated carboxylic acid such as maleic anhydride or a derivative thereof onto a polyolefin resin. The melting point of adhesive resin (B) is preferably 150°C or higher and 175°C or lower. The melting point of adhesive resin (B) mainly depends on the polyolefin resin before carboxylic acid modification. The same information described for polyolefin resin (C) described later can be applied to the polyolefin resin.

[0056] The proportion of carboxylic acid-modified polyolefin resin in 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 solely of carboxylic acid-modified polyolefin resin. Similarly, the proportion of adhesive resin (B) in layer (Y) 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 solely of adhesive resin (B).

[0057] <Polyolefin Resin (C)> The multilayer film of the present invention has a layer (Z) mainly composed of a polyolefin resin (C) having a melting point of 150°C or more and 175°C or less. The polyolefin resin (C) is not particularly limited as long as it is a polyolefin with a melting point of 150°C or more and 175°C or less, and examples include polypropylene, poly-methyl-1-pentene, ethylene-propylene copolymer, copolymer of ethylene and α-olefin having 4 or more carbon atoms, ethylene-vinyl ester copolymer, ethylene-acrylic acid ester copolymer, ethylene-acrylic acid copolymer, etc., with a melting point of 150°C or more and 175°C or less. From the viewpoint of improving the heat resistance of the multilayer structure, it is preferable that the polyolefin resin (C) mainly contains polypropylene, and more preferably polypropylene.

[0058] The effects of the present invention become more pronounced when the melting point of the polyolefin resin (C) is 150°C or higher and 175°C or lower. The melting point is preferably 153°C or higher, more preferably 155°C or higher, even more preferably 157°C or higher, and particularly preferably 158°C or higher. On the other hand, the melting point of the polyolefin resin (C) is preferably 172°C or lower, and more preferably 168°C or lower. Furthermore, from the viewpoint of achieving both high rigidity and toughness and high productivity (achieving high discharge volume during extrusion molding), the melt flow rate (MFR) (at 230°C and under a 2160g load) of the polyolefin resin (C), measured according to the method described in JIS K7210 (2014), is preferably 0.1 to 15 g / 10 min, more preferably 0.5 to 10 g / 10 min, and even more preferably 1 to 5 g / 10 min.

[0059] The polyolefin resin (C) preferably contains polypropylene as its main component, and the polypropylene content 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 polypropylene. Furthermore, the proportion of the polyolefin resin (C) in the layer (Z) 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 polyolefin resin (C).

[0060] Layer (Y) and layer (Z) mainly contain adhesive resin (B) and polyolefin resin (C), respectively. However, these layers may also contain other components such as antioxidants, plasticizers, heat stabilizers (melt stabilizers), photoinitiators, deodorizers, ultraviolet absorbers, antistatic agents, lubricants, colorants, fillers, desiccants, fillers, pigments, dyes, processing aids, flame retardants, and antifogging agents, as long as the effects of the present invention are not hindered. However, the total amount of these components is less than 50% by mass of 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.

[0061] <Multilayer Structure> The multilayer structure of the present invention has layer (X) as the outermost layer, and has a configuration in which at least layers (X), layer (Y), and layer (Z) are stacked adjacent to each other in this order. There may be multiple layers of each of layers (X), layer (Y), and layer (Z). Examples of the layer configuration of the multilayer film of the present invention include X / Y / Z, X / Y / Z / Y / X, X / Y / Z / Y / X / Y / Z / Y / X, etc.

[0062] From the viewpoint of gas barrier properties, recyclability, and economic efficiency, the thickness of layer (X) in the multilayer structure of the present invention is preferably 0.1 to 20 μm. It is also preferable that the ratio of the thickness of layer (X) to the total thickness of all layers in the multilayer structure is less than 25%. The thickness of layer (X) is more preferably 0.3 μm or more, and even more preferably 0.5 μm or more. On the other hand, the thickness of layer (X) is more preferably 10 μm or less, and even more preferably 5 μm or less. The ratio of the thickness of layer (X) to the total thickness of all layers in the multilayer film is more preferably less than 20%, and even more preferably less than 15%. The total thickness of all layers in the multilayer film is usually 15 to 250 μm, and preferably 20 to 100 μm. When the multilayer structure is stretched as described later, the total thickness of all layers after stretching is preferably 10 μm or more and less than 50 μm, and more preferably less than 40 μm. Suitable embodiments of such a multilayer structure include multilayer films or multilayer sheets, co-extrusion blow molded containers, co-injection blow molded containers, and the like.

[0063] The multilayer structure of the present invention may be stretched in at least one axis direction (uniaxial or biaxial direction) (stretched multilayer film or stretched multilayer sheet). Stretching in one or two axes can improve the mechanical properties and gas barrier properties of the resulting multilayer structure. From the viewpoint of economic efficiency and ease of tearing (making it easy to open packaging materials), the multilayer structure is preferably uniaxially stretched. From the viewpoint of obtaining a multilayer structure with less anisotropy in mechanical properties and greater toughness, the multilayer structure is preferably biaxially stretched. From the viewpoint of uniformity of thickness and mechanical strength of the resulting multilayer structure, it is preferable that it is stretched at least twice in one axis direction, and more preferably three times. In the case of a uniaxially stretched multilayer structure, it is preferable that it is stretched 2 to 12 times in one axis direction, and more preferably 4 to 10 times. In the case of a biaxially stretched multilayer film, it is preferable that it is stretched 3 to 12 times in each of the two axes, and more preferably 4 to 10 times. A heat-shrinkable film or sheet is also a preferred embodiment of the present invention. This can be manufactured by leaving the residual stress of the stretched film or sheet as described above without relieving it.

[0064] The method for manufacturing the multilayer structure of the present invention is not particularly limited, and conventional methods such as co-extrusion molding, co-injection molding, inflation molding, and blow molding can be employed. Preferred embodiments of the multilayer structure thus obtained include multilayer films or multilayer sheets, extruded articles, co-extruded blow-molded containers, and co-injection blow-molded containers. Among these, the co-extrusion method, in which each resin is extruded from separate dies or a common die and laminated, is preferred. Thus, it is preferable that the multilayer structure is an extruded article obtained by the co-extrusion method, and more preferably a multilayer film. Either an annular die or a T-die can be used as the die. The method of stretching in the uniaxial or biaxial direction is also not particularly limited, and it can be manufactured by stretching the film in the direction of flow and / or in the direction perpendicular to the flow direction, i.e., in the width direction, using conventionally known stretching methods such as roll-type uniaxial stretching, tubular-type simultaneous biaxial stretching, tenter-type sequential biaxial stretching, and tenter-type simultaneous biaxial stretching. Among these, the effects of the present invention are particularly pronounced in the case of a multilayer structure manufactured by tenter-type sequential biaxial stretching. Specifically, even when tenter-stretched at high temperatures, the ends of the multilayer structure are less likely to break. The stretching temperature may be 40 to 160°C from the viewpoint of processability. Since the ends of the multilayer structure are less likely to break even when tenter-stretched at high temperatures, the stretching temperature may be as high as 150°C or higher. If necessary, after the stretching process, a heat treatment may be performed at a temperature above the glass transition point and below the melting point to increase the degree of crystallinity and fix the orientation of the molecular chains, in a so-called heat-fixing operation.

[0065] The multilayer structure may be subjected to secondary processing. Examples of secondary processing methods include uniaxial stretching and biaxial stretching as described above, as well as stretch blow molding, thermoforming, and rolling. The thermoformed product obtained in this way is also a preferred embodiment of the multilayer structure. Furthermore, a fuel container made of the multilayer structure is also a preferred embodiment of the present invention. As the fuel container, a co-extruded blow-molded container or a thermoformed container is preferred.

[0066] <Inorganic Vapor Deposition Layer> The above problems can also be solved by a vapor-deposited multilayer film having an inorganic vapor deposition layer on the exposed side of layer (X) of the multilayer structure (extruded product) obtained by co-extrusion molding. The inorganic vapor deposition layer is made of inorganic materials such as metals and inorganic oxides and is a layer that has gas barrier properties against oxygen and water vapor. Layer (X) has a higher affinity for metals and inorganic oxides compared to ordinary thermoplastic resins, and a dense and defect-free inorganic vapor deposition layer can be formed, resulting in good interlayer adhesion between layer (X) and the inorganic vapor deposition layer in the obtained vapor-deposited multilayer film. In addition, because layer (X) has gas barrier properties, even if defects occur in the inorganic vapor deposition layer due to bending, etc., the decrease in gas barrier properties can be suppressed. The thickness of the inorganic vapor deposition layer is generally less than 500 nm. A thickness of less than 500 nm provides excellent viscosity stability when melt-molding pulverized multilayer structures containing the inorganic vapor deposition layer, and suppresses the generation of gels and lumps. On the other hand, the thickness of the inorganic vapor deposition layer is usually 10 nm or more.

[0067] The inorganic vapor-deposited layer is preferably either a metal vapor-deposited layer containing aluminum as the main component, or an inorganic oxide vapor-deposited layer containing alumina or silica as the main component. A metal vapor-deposited layer is preferred when light shielding is required, but an inorganic oxide vapor-deposited layer is preferred from the viewpoint of visibility of the contents as a packaging material, microwave suitability, and suppression of gel and lumps when melt-molding crushed material.

[0068] The metal vapor deposition layer is generally a layer containing aluminum as its main component. The aluminum atom content in the metal vapor deposition layer is preferably 50 mol% or more, more preferably 70 mol% or more, even more preferably 90 mol% or more, and particularly preferably 95 mol% or more. The average thickness of the metal vapor deposition layer is preferably 120 nm or less, more preferably 100 nm or less, and even more preferably 90 nm or less. Furthermore, the average thickness of the metal vapor deposition layer is preferably 25 nm or more, more preferably 35 nm or more, and even more preferably 45 nm or more. The average thickness of the metal vapor deposition layer is the average value of the thickness at any 10 points on the cross-section of the metal vapor deposition layer measured by an electron microscope. When the multilayer film of the present invention has a metal vapor deposition layer, the light transmittance at a wavelength of 600 nm can be set to 10% or less, and it has excellent light-shielding properties.

[0069] The inorganic oxide vapor-deposited layer is a vapor-deposited film of an inorganic oxide, such as an oxide of silicon, aluminum, magnesium, calcium, potassium, tin, sodium, boron, titanium, lead, zirconium, or yttrium, preferably alumina or silica. The average thickness of the inorganic oxide vapor-deposited layer is preferably 60 nm or less, more preferably 50 nm or less, and even more preferably 40 nm or less. Furthermore, the average thickness of the inorganic oxide vapor-deposited layer is preferably 10 nm or more, more preferably 15 nm or more, and even more preferably 20 nm or more. The average thickness of the inorganic oxide vapor-deposited layer is the average value of the thickness at any 10 points on the cross-section of the inorganic oxide vapor-deposited layer measured by an electron microscope. When the multilayer film of the present invention has an inorganic oxide vapor-deposited layer, the light transmittance at a wavelength of 600 nm can be 80% or more, and the visibility of the contents when used as a packaging material is excellent. From the viewpoint of further improving visibility, a light transmittance of 90% or more at a wavelength of 600 nm is more preferable. The light transmittance can be increased, for example, by suppressing thickness unevenness of the multilayer film of the present invention used in the manufacture of the vapor-deposited multilayer film. The multilayer film of the present invention tends to exhibit high light transmittance because the outermost layer (X) mainly contains a modified vinyl alcohol polymer (a) with a melting point of 150°C or higher, thus suppressing thickness variations. A means to further suppress thickness variations in the multilayer film of the present invention is, for example, stretching in at least one axial direction. The light transmittance of the multilayer film of the present invention at a wavelength of 600 nm is preferably 80% or higher, and more preferably 90% or higher.

[0070] The inorganic vapor-deposited layer can be formed by known physical vapor deposition methods or chemical vapor deposition methods. Specifically, examples include vacuum vapor deposition, sputtering, ion plating, ion beam mixing, plasma CVD, laser CVD, MO-CVD, and thermal CVD, but it is preferable to use a physical vapor deposition method, and among these, vacuum vapor deposition is particularly preferable. The upper limit of the surface temperature of layer (X) during the formation of the inorganic vapor-deposited layer is preferably 60°C, more preferably 55°C, and even more preferably 50°C. The lower limit of the surface temperature of layer (X) during the formation of the inorganic vapor-deposited layer is not particularly limited, but it is preferably 0°C, more preferably 10°C, and even more preferably 20°C. Before forming the layer, the exposed surface of layer (X) may be plasma-treated. Known methods can be used for this plasma treatment, and atmospheric pressure plasma treatment is preferred. In atmospheric pressure plasma treatment, nitrogen, helium, neon, argon, krypton, xenon, radon, etc., can be used as the discharge gas. Among these, nitrogen, helium, and argon are preferred, and nitrogen is particularly preferred because it can reduce costs.

[0071] A protective layer (topcoat layer) may be provided on the inorganic vapor deposition layer as needed, provided that it does not hinder the effects of the present invention. The protective layer may be a layer containing a resin such as a water-soluble polymer, ethylene-vinyl alcohol copolymer, polyester, or acrylic resin, and is preferably a layer containing a water-soluble polymer. Examples of the water-soluble polymer include polyvinyl alcohol, polyvinylpyrrolidone, starch, methylcellulose, carboxymethylcellulose, and sodium alginate. Among these, polyvinyl alcohol is preferred from the viewpoint of gas barrier properties. The degree of saponification of polyvinyl alcohol is not particularly limited and may be 60 mol% to 100 mol%. The protective layer can be formed by dissolving these resins in a solvent and coating them.

[0072] The protective layer may contain an inorganic compound in addition to the above resin. Examples of the inorganic compound include metal alkoxides or their hydrolysates, and may contain both. The metal alkoxide has the general formula M(OR). ｎ (M: metals such as Si, Ti, Al, Zr, R: CH ３ , C ２H ５ These are compounds represented by alkyl groups such as . Among them, tetraethoxysilane [Si(OC ２ H ５ ) ４ ], triisopropoxyaluminum [Al(O-iso-C ３ H ７ ) ３ ] is preferred because it is relatively stable in aqueous solvents after hydrolysis.

[0073] The protective layer is particularly preferably a layer containing a water-soluble polymer and a metal alkoxide and / or its hydrolysate. Such a protective layer can be formed by preparing a coating solution by mixing an aqueous solvent (water or a water / alcohol mixed solvent), a water-soluble polymer, and a metal alkoxide and / or its hydrolysate, coating it onto an inorganic vapor-deposited layer, and then heating and drying it. Known additives such as isocyanate compounds, silane coupling agents, dispersants, stabilizers, viscosity modifiers, and colorants may be added to the above solution, to the extent that they do not impair the gas barrier properties. The content of the water-soluble polymer in the above solution is preferably 20% to 50% by mass of the total solid content.

[0074] Furthermore, the protective layer may be a gas barrier adhesive layer. The gas barrier adhesive layer is a layer formed from an adhesive capable of exhibiting gas barrier properties. Examples of such adhesives include epoxy adhesives and polyester / polyurethane adhesives. For example, "Maxive" from Mitsubishi Gas Chemical Company, Inc. and "Paslim" from DIC Corporation can be used. Such a protective layer can be formed by coating the inorganic vapor-deposited layer with the adhesive, drying it, and curing it as needed. When the protective layer is a gas barrier adhesive layer, the resin layer (R) can be laminated onto the vapor-deposited multilayer film described later without the need for other adhesive layers.

[0075] The thickness of the protective layer is, for example, 0.01 to 50 μm, preferably 0.1 to 20 μm, and may be 0.5 to 10 μm or 1 to 5 μm.

[0076] <Laminate> The multilayer film (extruded product) or the vapor-deposited multilayer film itself can be used as a packaging material having gas barrier properties. However, by laminating it with at least one resin layer (R) mainly composed of a thermoplastic resin (D), various functions as a packaging material, such as aesthetic appeal and heat sealability, can be added. The thermoplastic resin (D) is not particularly limited and includes 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 with 4 to 20 carbon atoms), polybutene, polypentene, and other olefins alone or copolymers thereof, nylon 6, nylon 6,6 and other polyamides, polyesters such as polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, polystyrene, polyvinyl chloride, polyvinylidene chloride, acrylic resin, polycarbonate, chlorinated polyethylene, chlorinated polypropylene, and the like. Among these, polyolefins are preferred from the viewpoint of excellent moisture resistance, mechanical properties, economy, and heat sealability, and polyamides and polyesters are preferred from the viewpoint of excellent mechanical properties and heat resistance. In particular, in order to obtain a multilayer structure with excellent recyclability, the thermoplastic resin (D) is preferably of the same type as the polyolefin resin (C) described above, that is, a polyolefin resin with a melting point of 150°C or more and 175°C or less, more preferably containing polypropylene as the main component, and even more preferably being polypropylene. Such resin layer (R) may be unstretched, or it 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, an unstretched layer is preferred.

[0077] The method for forming the resin layer (R) is not particularly limited, but is generally formed by melt extrusion using an extruder. Either an annular die or a T-die can be used as the die. The method of stretching in the uniaxial or biaxial direction is also not particularly limited, and the film can be manufactured by stretching it in the direction of film flow and / or in the direction perpendicular to the flow direction, i.e., in the width direction, using conventionally known stretching methods such as roll-type uniaxial stretching, tubular-type simultaneous biaxial stretching, tenter-type sequential biaxial stretching, and tenter-type simultaneous biaxial stretching. From the viewpoint of uniformity of the thickness of the resulting layer and mechanical strength, the stretching ratio is preferably 8 to 60 times the area ratio. An area ratio of 55 times or less is more preferable, and 50 times or less is even more preferable. An area ratio of 9 times or more is even more preferable. 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.

[0078] From the viewpoint of industrial productivity, the thickness of the resin layer (R) is preferably 10 to 200 μm. Specifically, the thickness is more preferably 10 to 150 μm for an unstretched layer, and more preferably 10 to 50 μm for a biaxially oriented layer.

[0079] Furthermore, the total thickness of the laminate is preferably 300 μm or less. Because the total thickness is within this range, the laminate is lightweight and flexible, making it suitable for flexible packaging applications. Additionally, the amount of resin used in the laminate is small, thus reducing the environmental impact.

[0080] The thickness of each layer in the laminate can be adjusted as appropriate depending on the application, but from the viewpoint of suppressing discoloration during melt molding of pulverized material, improving thermal stability during melt molding, and suppressing the generation of lumps, at least one of the layers (Z) and resin layer (R) contains polypropylene as the main component, and the ratio of the total thickness of the layers containing polypropylene as the main component to the total thickness of the laminate is preferably 0.75 or more, and more preferably 0.85 or more. On the other hand, from the viewpoint of improving gas barrier properties, the ratio is preferably 0.98 or less.

[0081] The method for laminating the resin layer (R) onto the multilayer film or the vapor-deposited multilayer film is not particularly limited and includes, for example, extrusion lamination, co-extrusion lamination, dry lamination, etc. When laminating the resin layer (R) onto the multilayer film or the vapor-deposited multilayer film, an adhesive layer may be provided. That is, each layer constituting the laminate may be laminated via an adhesive layer as needed. However, there is no adhesive layer between layers (X) and (Y) and between layers (Y) and (Z) of the multilayer film or the vapor-deposited multilayer film. The adhesive layer can be formed by coating and drying a known adhesive. A two-component reaction type polyurethane adhesive, which is obtained by mixing and reacting a polyisocyanate component and a polyol component, is preferred. The thickness of the adhesive layer is not particularly limited, but is preferably 1 to 5 μm, and more preferably 2 to 4 μm.

[0082] The following are examples of layer configurations for the laminate. In the following layer configurations, layer (X) is denoted as X, layer (Y) as Y, layer (Z) as Z, inorganic vapor deposition layer as I, protective layer as T, and layer (R) as R, where " / " means that the layers are directly laminated and " / / " means that the layers are laminated via an adhesive layer. (1) Z / Y / X / / R (2) Z / Y / X / I / / R (3) Z / Y / X / I / T / R (4) Z / Y / X / I / T / R (5) R / / Z / Y / X / / R (6) R / / Z / Y / X / I / / R (7) R / / Z / Y / X / I / T / R (8) R / / Z / Y / X / I / T / / R In the above layer configurations, it is preferable that layer (X), layer (Y), and layer (Z) are stretched in at least one axial direction, and more preferably that they are biaxially stretched. Layers (Z) and (R) are preferably composed mainly of polypropylene, and layer (Y) is preferably composed mainly of maleic anhydride-modified polypropylene. Layer (X) is a layer made of a resin composition (A) mainly containing a modified vinyl alcohol polymer (a) having a modified group containing a primary hydroxyl group.

[0083] The laminate may have other layers besides those described above, as long as they do not impede the effects of the present invention. An example of other layers is a recovery layer. Another example of other layers is a printing layer. The printing layer may be included at any position in the laminate. The printing layer may be, for example, a film obtained by coating a solution containing a pigment or dye and, optionally, a binder resin, and drying it. Methods for coating the printing layer include gravure printing, as well as various coating methods using wire bars, spin coaters, die coaters, etc. The thickness of the ink layer is not particularly limited, but is preferably 0.5 to 10 μm, and more preferably 1 to 4 μm.

[0084] Because the laminate has excellent appearance and gas barrier properties, it can be suitably used as a material for various types of packaging, such as food packaging, pharmaceutical packaging, industrial chemical packaging, and pesticide packaging.

[0085] The present invention will be described in more detail below using examples.

[0086] [Production Example 1] (1) A 250 L pressurized reactor equipped with a modified EVAc synthesis jacket, stirrer, nitrogen inlet, ethylene inlet, and initiator addition port was charged with 100 kg of vinyl acetate (hereinafter referred to as VAc), 10 kg of methanol (hereinafter sometimes referred to as MeOH), and 2.9 kg of 2-methylene-1,3-propanediol diacetate (hereinafter referred to as MPDAc). After raising the temperature to 60°C, the reactor was purged with nitrogen by bubbling with nitrogen for 30 minutes. Then, ethylene was introduced so that the reactor pressure (ethylene pressure) was 4.9 MPa. After adjusting the temperature inside the reactor to 60°C, 45 g of 2,2'-azobis (2,4-dimethylvaleronitrile) (Wako Pure Chemical Industries, Ltd. "V-65") was added as a methanol solution as an initiator, and polymerization was started. During polymerization, the ethylene pressure was maintained at 4.9 MPa and the polymerization temperature at 60°C. After 6 hours, when the polymerization rate of VAc reached 33%, the polymerization was stopped by cooling. The reaction vessel was opened to remove ethylene, and then nitrogen gas was bubbled in to completely remove ethylene. Next, unreacted VAc was removed under reduced pressure, and then MeOH was added to the modified ethylene-vinyl acetate copolymer (hereinafter sometimes referred to as modified EVAc), in which structural units derived from MPDAc were introduced by copolymerization, to obtain a 20% by mass MeOH solution.

[0087] (2) A 20% by mass MeOH solution of the modified EVAc obtained in (1) was charged into a 500 L reaction vessel equipped with a saponification jacket for modified EVAc, a stirrer, a nitrogen inlet, a reflux condenser, and a solution addition port. The temperature of this solution was raised to 60°C while blowing nitrogen into it, and 0.5 equivalents of sodium hydroxide were added to the vinyl acetate units in the modified EVAc as a 2 N MeOH solution. After the addition of the sodium hydroxide MeOH solution was completed, the system temperature was maintained at 60°C, and the saponification reaction was carried out by stirring for 2 hours while methyl acetate and MeOH were distilled off. Then acetic acid was added to stop the saponification reaction. Subsequently, while heating and stirring at 60-80°C, deionized water was added, and MeOH was distilled off from the reaction vessel, causing modified EVOH to precipitate. The precipitated modified EVOH was collected and pulverized in a mixer. The obtained modified EVOH powder was placed in a 1 g / L aqueous acetic acid solution (bath ratio 20: 20 L of aqueous solution per 1 kg of powder) and stirred and washed at 20°C for 2 hours. After dewatering, it was placed in another 1 g / L aqueous acetic acid solution (bath ratio 20) and stirred and washed at 20°C for 2 hours. The dewatered mixture was then placed in ion-exchanged water (bath ratio 20) and stirred and washed at 20°C for 2 hours, and this process was repeated three times to purify the mixture. Next, the mixture was immersed in 10 L of an aqueous solution containing 0.5 g / L acetic acid and 0.1 g / L sodium acetate, stirred and washed at 20°C for 4 hours, then dewatered. After drying at 60°C for 16 hours, it was dried at 110°C for 16 hours to obtain resin composition A1, which mainly contains modified EVOH. The melt flow rate (MFR) of the obtained resin composition A1 (190°C, under a 2160 g load) was 5.0 g / 10 min. Furthermore, the modified EVOH obtained had a modified group containing a primary hydroxyl group represented by formula (I), where X was a hydroxymethyl group and Y was a hydrogen atom.

[0088] (3) Content of each structural unit in modified EVAc The content of ethylene units, vinyl acetate units, and structural units derived from MPDAc in modified EVAc (content of modified groups including primary hydroxyl groups represented by formula (I)) is calculated based on the modified EVAc before saponification. １ The results were calculated using H-NMR measurements.

[0089] First, a small sample of the MeOH solution of the modified EVAc obtained in (1) was taken, and the modified EVAc was precipitated in ion-exchanged water. The precipitate was collected and dried under vacuum at 60°C to obtain a dried product of modified EVAc. Next, the obtained dried product of modified EVAc was dissolved in dimethyl sulfoxide (DMSO)-d6 containing tetramethylsilane as an internal standard, and heated at 500 MHz. １ The measurement was performed at 80°C using H-NMR (manufactured by JEOL Ltd.: "GX-500").

[0090] Modified EVAc １ Each peak in the 1H-NMR spectrum is assigned as follows: • 0.6–1.0 ppm: Methylene proton (4H) of the terminal ethylene unit • 1.0–1.85 ppm: Methylene proton (4H) of the intermediate ethylene unit, methylene proton (2H) of the main chain of the structural unit derived from MPDAc, and methylene proton (2H) of the vinyl acetate unit • 1.85–2.1 ppm: Methyl proton (6H) of the structural unit derived from MPDAc and methyl proton (3H) of the vinyl acetate unit • 3.7–4.1 ppm: Methylene proton (4H) of the side chain of the structural unit derived from MPDAc • 4.4–5.3 ppm: Methyl proton (1H) of the vinyl acetate unit

[0091] According to the above attribution, if the integral value for 0.6 to 1.0 ppm is x, the integral value for 1.0 to 1.85 ppm is y, the integral value for 3.7 to 4.1 ppm is z, and the integral value for 4.4 to 5.3 ppm is w, then the content of ethylene units (a: mol%), vinyl acetate units (b: mol%), and structural units derived from MPDAc (c: mol%) are calculated according to the following formulas: a = (2x + 2y - z - 4w) / (2x + 2y + z + 4w) × 100 b = 8w / (2x + 2y + z + 4w) × 100 c = 2z / (2x + 2y + z + 4w) × 100

[0092] As calculated using the above method, the ethylene unit content of modified EVAc in Production Example 1 was 38.0 mol%, the vinyl acetate unit content was 60.5 mol%, and the structural unit content derived from MPDAc was 1.5 mol%. The ethylene unit content, vinyl acetate unit content, and structural unit content derived from MPDAc at this time are the same as the total content of ethylene units, vinyl acetate units, and vinyl alcohol units in modified EVOH after saponification, as well as the content of the modified group containing a primary hydroxyl group represented by formula (I).

[0093] (4) Degree of saponification of denatured EVOH The same applies to denatured EVOH after saponification. １ ¹H-NMR measurements were performed. The modified EVOH obtained in (2) above was dissolved in dimethyl sulfoxide (DMSO)-d6 containing tetramethylsilane as an internal standard and tetrafluoroacetic acid (TFA) as an additive, and NMR was performed at 500 MHz. １ The measurement was performed at 80°C using H-NMR (manufactured by JEOL Ltd.: "GX-500"). １ ¹H-NMR measurements showed a significant decrease in peak intensity between 1.85 and 2.1 ppm, indicating that, in addition to the ester groups derived from vinyl acetate in the modified EVOH, the ester groups contained in the structural units derived from MPDAc were also saponified and converted into hydroxyl groups. The result obtained in Production Example 1 １ A decrease in peak intensity between 1.85 and 2.1 ppm was also observed in the 1H-NMR spectrum. The degree of saponification was calculated from the peak intensity ratio of methyl protons of vinyl acetate units (1.85–2.1 ppm) and methine protons of vinyl alcohol units (3.15–4.15 ppm). The degree of saponification of the modified EVOH from Production Example 1 was 99.9 mol% or higher.

[0094] (5) Melting point of modified EVOH The modified EVOH obtained in (2) above (modified EVOH removed after washing with deionized water and before stirring and immersing in an aqueous solution containing acetic acid and sodium acetate) was heated from 20°C to 220°C at a rate of 10°C / min using a differential scanning calorimetry analyzer (TA Instruments "Q2000"). Then it was cooled to 20°C at a rate of 10°C / min, and then heated again from 20°C to 220°C at a rate of 10°C / min. The temperature of the maximum endothermic peak during the second heating was determined and this was taken as the melting point. As a result, the melting point of modified EVOH was found to be 160°C. The melting points of adhesive resin (B) and polyolefin resin (C) can also be measured by the above method.

[0095] (6) Content of alkali metal ions (b) and boron compounds in the resin composition 0.5 g of the resin composition A1 obtained in (2) above was placed in a Teflon® pressure vessel, and 5 mL of concentrated nitric acid was added and decomposed at room temperature for 30 minutes. After decomposition, the vessel was covered and further decomposed by heating at 150°C for 10 minutes, then at 180°C for 5 minutes, using a wet decomposition apparatus (MWS-2, manufactured by Actac Co., Ltd.), and then cooled to room temperature. This processed solution was transferred to a 50 mL volumetric flask and diluted with pure water. The content of alkali metal ions (b) and boron compounds (in terms of boron element) was quantified by measuring this solution using an ICP emission spectrometer (Optima 4300DV, manufactured by Perkin Elmer). The content of each component was 200 ppm for sodium ions and 0 ppm for boron compounds. The content of polyvalent metal ions (c) in the resin composition can also be measured by the same method.

[0096] (7) Melt viscosity of the resin composition The melt viscosity of the resin composition A1 obtained in (2) above was measured using a capillary rheometer "Capillograph 1D" manufactured by Toyo Seiki Seisakusho Co., Ltd. Before measurement, the resin composition A1 was dried at 90°C, and with a moisture content of 0.3% or less, the measurement temperature was 210°C and the shear rate was 12 sec. －１ and 120 sec －１ Measurements were taken within the specified range.

[0097] (8) MFR of the resin composition The MFR (at 190°C and under a 2160g load) of the resin composition A1 obtained in (2) above was measured in accordance with the method described in JIS K7210 (2014). The MFR of the adhesive resin (B) and the polyolefin resin (C) can be measured at 230°C and under a 2160g load in accordance with the above method.

[0098] [Production Example 2] 10 kg of resin composition A1 obtained in Production Example 1 was mixed with 100 mL of a 50 g / L boric acid aqueous solution. After standing for 24 hours to allow the boric acid aqueous solution to be adsorbed onto the modified EVOH, the mixture was fed into a twin-screw extruder (screw diameter: 30 mmφ, L / D = 30), and twin-screw kneading was carried out at an extrusion temperature of 200°C. The resin that came out in strand form was cooled and solidified in a water bath and cut into pellets with a strand cutter. After drying at 60°C for 16 hours, resin composition A2 was obtained by drying at 110°C for 16 hours. The MFR (at 190°C and under a 2160 g load) of the obtained resin composition A2 was 3.0 g / 10 min. The alkali metal ion and boron compound content was 200 ppm for sodium ions and 87 ppm for boric acid in terms of boron element.

[0099] [Production Examples 3-11] Resin compositions A3-A7 and B1-B5 were obtained in the same manner as in Production Example 1, except that the polymerization conditions (in-tank pressure during polymerization, polymerization time, amount of methanol added, type or amount of monomer represented by the above formula (II), amount of initiator added, and polymerization rate of VAc) were changed so that the ethylene unit content, type or content of modified group units containing primary hydroxyl groups, MFR and melt viscosity were as shown in Table 1.

[0100] [Example 1] (1) Production of unoriented multilayer film Using the resin composition A1 obtained in Production Example 1, polypropylene (Novatec® PP FL203D manufactured by Nippon Polypropylene Co., Ltd.; melting point 158°C), and polypropylene adhesive resin (Admer® QF500 manufactured by Mitsui Chemicals, Inc.; maleic anhydride graft-modified polypropylene adhesive resin, melting point 159°C), three types of three-layer unoriented multilayer films (resin composition / polypropylene adhesive resin / polypropylene = 18 μm / 18 μm / 144 μm) were produced. The thickness of the co-extruded film was adjusted by appropriately changing the screw rotation speed and the take-up roll speed. The extruder, extrusion conditions, and die used were as follows. Resin composition extruder: Single-screw extruder (Toyo Seiki Co., Ltd. Lab machine ME type CO-EXT) Screw: 20 mm diameter, L / D 20, full-flight screw Extrusion temperature: Feed section / compression section / metering section / die = 175 / 200 / 230 / 230℃ Polypropylene adhesive resin extruder: Single-screw extruder (Technovel Co., Ltd. SZW20GT-20MG-STD) Screw: 20 mm diameter, L / D 20, full-flight screw Extrusion temperature: Feed section / compression section / metering section / die = 175 / 200 / 230 / 230℃ Polypropylene resin extruder: Single-screw extruder (Plastics Engineering Laboratory Co., Ltd. GT-32-A) Screw: 32 mm diameter, L / D 28, full-flight screw Extrusion temperature: Feed section / compression section / metering section / die = 175 / 200 / 230 / 230℃ Die: 300mm wide, 3 types, 3-layer coat hanger die (manufactured by Plastics Engineering Laboratory Co., Ltd.) Die temperature: 230℃

[0101] (2) Manufacturing of biaxially oriented multilayer film S1 The unoriented multilayer film obtained in (1) was preheated at 120°C for 30 seconds using a tenter-type sequential biaxial stretching equipment, then stretched three times in the longitudinal direction, then preheated at 150°C for 30 seconds, then stretched three times in the transverse direction, and then heat-set at 150°C for 30 seconds to obtain a biaxially oriented multilayer film S1 of three types and three layers (resin composition / polypropylene adhesive resin / polypropylene = 2 μm / 2 μm / 16 μm).

[0102] (3) Manufacturing of biaxially oriented multilayer film S2 The unoriented multilayer film obtained in (1) was preheated at 120°C for 10 seconds using a tenter-type sequential biaxial stretching equipment, then stretched three times in the longitudinal direction, then preheated at 150°C for 10 seconds, then stretched three times in the transverse direction, and then heat-set at 150°C for 10 seconds to obtain a biaxially oriented multilayer film S2 of three types and three layers (resin composition / polypropylene adhesive resin / polypropylene = 2 μm / 2 μm / 16 μm).

[0103] (4) Production of vapor-deposited biaxially oriented multilayer films A 50 nm thick aluminum metal vapor deposition was carried out on the surface of the resin composition layer of the biaxially oriented multilayer films S1 and S2 obtained in (2) and (3) by a known vacuum deposition method to obtain metal vapor-deposited biaxially oriented multilayer films D1 and D2 (aluminum metal vapor deposition film / resin composition / polypropylene adhesive resin / polypropylene = 50 nm / 2 μm / 2 μm / 16 μm).

[0104] (5) Manufacturing of the laminate A two-component adhesive ("Takelac® A-520" and "Takenate® A-50" manufactured by Mitsui Chemicals, Inc.) was applied to one side of an unoriented polypropylene film ("GLC" manufactured by Mitsui Chemicals Tohcello Co., Ltd., 50 μm thick, melting point 163°C, polypropylene content of 80% by mass or more) to a dry thickness of 2 μm and dried, and laminated with the vapor-deposited side of the vapor-deposited biaxially oriented multilayer films D1 and D2 obtained in (4) to obtain laminates L1 and L2 (polypropylene / adhesive / aluminum metal vapor-deposited film / resin composition / polypropylene adhesive resin / polypropylene = 50 μm / 2 μm / 50 nm / 2 μm / 2 μm / 16 μm).

[0105] (6) Appearance evaluation of the layer (X) side of the multilayer film The appearance of the layer (X) side of the biaxially oriented multilayer film S1 obtained in (2) was visually observed and judged according to the following criteria. The results are shown in Table 1. Judgment: Criteria A: No unevenness, uniform appearance B: Slight unevenness and / or streaks are visible C: Unevenness and / or streaks are visible D: Significant unevenness and / or streaks are visible E: Severe unevenness and / or streaks are visible, or cracks are visible

[0106] (7) Evaluation of stretchability (tear at the edges during stretching) When removing the biaxially oriented multilayer film S1 obtained in (2) from 24 stainless steel film-supporting clips of a biaxial stretching apparatus at 150°C, the number of places where the edges tore was evaluated when the 24 clips holding the film were removed one by one in a clockwise direction. The results are shown in Table 1. Judgment: Criteria A: No tears B: 1 to 4 tears C: 5 or more tears

[0107] (8) Evaluation of thickness unevenness of layer (X) For the biaxially oriented multilayer film S1 obtained in (2), a total of five sections were cut from the center in the width direction at 30 mm intervals, and the film was cut using a microtome. The thickness of layer (X) was measured using an ultra-high resolution electrolytic emission scanning electron microscope (SU8600, Hitachi High-Technologies Corporation). The thickness unevenness of layer (X) was evaluated by the standard deviation of the thickness according to the following criteria. The results are shown in Table 1. Judgment: Criteria A: Less than ±0.3 μm B: ±0.3 μm or more, less than ±0.5 μm C: ±0.5 μm or more, less than ±1.0 μm D: ±1.0 μm or more

[0108] (9) Interlayer adhesion evaluation Laminates L1 [S1 (preheating 30 seconds, heat setting 30 seconds)] and L2 [S2 (preheating 10 seconds, heat setting 10 seconds)] obtained in (5) were conditioned at 23°C and 50% RH. Then, a sample 150 mm long and 15 mm wide was cut along the extrusion direction at a total of 5 locations at 30 mm intervals from the center in the width direction. The peel strength was measured using a Shimadzu Autograph "DCS-50M type tensile testing machine" at 23°C and 50% RH in a tensile speed of 250 mm / min in T-type peel mode, and the average value of the peel strength at the 5 locations was judged according to the following criteria. However, the peel interface is the resin composition / polypropylene adhesive resin interface. The results are shown in Table 1. Judgment Criteria A: 250g / 15mm or more B: 200g / 15mm or more and less than 250g / 15mm C: 150g / 15mm or more and less than 200g / 15mm D: 100g / 15mm or more and less than 150g / 15mm E: Less than 100g / 15mm

[0109] [Example 2] Manufacturing and evaluation were carried out in the same manner as in Example 1, except that resin compositions A2 to A7 and B1 to B5 were used instead of resin composition A1. The results are shown in Table 1.

[0110] [Examples 3-7 and Comparative Examples 1-5] Manufacturing and evaluation were carried out in the same manner as in Example 1, except that resin compositions A2-A7 and B1-B5 were used instead of resin composition A1, and laminate L2 (using S2) was not prepared. The results are shown in Table 1.

[0111]

Claims

1. A multilayer structure having layer (X) as the outermost layer, with at least layers (X), (Y), and (Z) stacked adjacently in this order, wherein layer (X) is made of a resin composition (A) mainly composed of a modified vinyl alcohol polymer (a) with a melting point of 150°C to 175°C, layer (Y) mainly composed of an adhesive resin (B), and layer (Z) mainly composed of a polyolefin resin (C) with a melting point of 150°C to 175°C, and the modified vinyl alcohol polymer (a) has a modified group containing a primary hydroxyl group represented by the following formula (I). [In the formula, one of X and Y is a hydrogen atom, and the other is a hydroxymethyl group or a 2-hydroxyethyl group.] 2. The multilayer structure according to claim 1, wherein the resin composition (A) contains 90% by mass or more of the modified vinyl alcohol polymer (a).

3. Resin composition (A) temperature 210°C, shear rate 12 sec －１ melt viscosity η １２ The multilayer structure according to claim 1, wherein the pressure is 2,000 Pa·s or less.

4. Resin composition (A) temperature 210°C, shear rate 120 sec －１ melt viscosity η １２０ The melt viscosity η １２ The ratio of (η １２ / η １２０ The multilayer structure according to claim 3, wherein the ratio is 1.5 or less.

5. The multilayer structure according to claim 1, wherein the content of the boron compound in the resin composition (A) is less than 30 ppm in terms of elemental boron.

6. The multilayer structure according to claim 1, which is stretched by at least twice its original length in at least one axial direction.

7. The multilayer structure according to claim 1, wherein the modified vinyl alcohol polymer (a) is a modified ethylene-vinyl alcohol copolymer having an ethylene unit content of 15 to 85 mol%.

8. The multilayer structure according to claim 1, wherein X in formula (I) is a hydroxymethyl group or a 2-hydroxyethyl group, and Y is a hydrogen atom.

9. An extruded article comprising a multilayer structure according to any one of claims 1 to 8.

10. A vapor-deposited multilayer film having an inorganic vapor-deposited layer on the exposed surface side of layer (X) of the extruded product according to claim 9.

11. A heat-shrinkable film or heat-shrinkable sheet comprising a multilayer structure according to any one of claims 1 to 8.

12. A co-extruded blow-molded container comprising a multilayer structure according to any one of claims 1 to 8.

13. A thermoformed article comprising a multilayer structure according to any one of claims 1 to 8.

14. A fuel container comprising a multilayer structure according to any one of claims 1 to 8.

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