Multilayer structure having paper layer and modified ethylene-vinyl alcohol copolymer layer

Abstract

To provide a multilayer structure that, while being a paper substrate, not only offers superior gas barrier properties but also preferably retains these superior properties after being bent.SOLUTION: A multilayer structure has a paper layer (A), and a modified ethylene-vinyl alcohol layer (E) including a modified ethylene-vinyl alcohol copolymer (e).SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a multilayer structure having excellent gas barrier properties.

Background Art

[0002] In order to suppress the oxidative deterioration of the contents, it is important to impart gas barrier properties to paper packaging. For this purpose, it has been proposed to laminate a gas barrier layer of a first layer containing an ethylene-modified polyvinyl alcohol resin and an inorganic layered compound on paper and a second layer made of ethylene-modified polyvinyl alcohol (Patent Document 1). In addition, a combination with sterilization technology is also used to extend the expiration date of the contents. There is a proposal for a retort paper cup as a paper barrier packaging material applied to retort sterilization technology (Patent Document 2).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0004] Although the laminate containing an ethylene-modified polyvinyl alcohol resin as described in Patent Document 1 has excellent gas barrier properties, cracks may occur in a package having an acute bending portion, and the preservability of the contents may deteriorate, and it has been found that there is room for improvement.

[0005] The present invention has been made based on the above circumstances, and an object thereof is to provide a multilayer structure that has good gas barrier properties while being a paper substrate and can maintain good gas barrier properties after bending.

Means for Solving the Problems

[0006] The present invention provides the following [1] to

[12] . [1] A multilayer structure comprising a paper layer (A) and a modified ethylene vinyl alcohol layer (E) containing a modified ethylene vinyl alcohol copolymer (e), A multilayer structure comprising a modified ethylene-vinyl alcohol copolymer (e) containing structural units (Ia), (Ib), and (Ic) represented by the following formulas, wherein the content (mol%) of the structural units (Ia), (Ib), and (Ic) a, b, and c satisfy the following formulas (1) to (3), and the degree of saponification (DS) of the modified ethylene-vinyl alcohol copolymer (e) represented by the following formula (4) is 90 mol% or more. 21 ≤ a ≤ 55 (1) 0.1 ≤ c ≤ 10 (2) [100-(a+c)]×0.9≦b≦[100-(a+c)] (3) DS = [(Total number of moles of hydrogen atoms among X, Y, and Z) / (Total number of moles of X, Y, and Z)] × 100 (4) [2] The basis weight of the paper layer (A) is 15 to 800 g / m² 2 It is preferable that this be the case. [3] It is also preferable that the modified ethylene-vinyl alcohol copolymer (e) contains alkali metal ions, with a content of 2.5 to 22 μmol / g. [4] Under conditions of 20°C and 65% RH, the oxygen permeability measured in accordance with JIS-K7126-2 (2006) Part 2 (isobaric method) is 20 cc / (m³ 2 It is also preferable that the value be less than or equal to (day·atm). [5] It is also preferable that the heat seal strength measured in 15 mm width in accordance with JIS Z 0238 is 300 gf / 15 mm or more. [6] It is also preferable to include an intermediate layer (F) and a sealant layer (G). [7] The intermediate layer (F) may also contain a thermosetting resin or a thermoplastic resin (f). [8] The sealant layer (G) may also contain a thermoplastic resin (g). [9] It is also preferable that the thermoplastic resin (f) and thermoplastic resin (g) include at least one selected from the group consisting of polyethylene, polypropylene, modified polyethylene, and modified polypropylene.

[10] It is also preferable that the weight M1 of the paper layer (A) and the total weight M2 of the other layers satisfy the following formula (5). 1 ≤ M1 / M2 ≤ 300 (5)

[11] A package using the multilayer structure described above, wherein the package has one or more folded portions, is also a preferred embodiment.

[12] It is also preferable that the contents of the package be food, and that the water activity of the food be 0.10 to 0.94.

[0007] [ka] [In the formula, a, b, and c are the content (mol%) of each structural unit relative to 100 mol% of the total structural units, and W is a methyl group or R 2 -OY represents a group, where X, Y, and Z each independently represent a hydrogen atom, a formyl group, or an alkanoyl group having 2 to 10 carbon atoms, and R1 represents a single bond, an alkylene group having 1 to 9 carbon atoms, or an alkylene oxy group having 1 to 9 carbon atoms. The alkylene group and the alkylene oxy group may also contain a hydroxyl group, an alkoxy group, or a halogen atom. 2 * represents an alkylene group having 1 to 9 carbon atoms or an alkylene oxy group having 1 to 9 carbon atoms, and the alkylene group and the alkylene oxy group may contain a hydroxyl group, an alkoxy group, or a halogen atom. * represents a bonding site. [Effects of the Invention]

[0008] According to the present invention, it is possible to provide a multilayer structure that has good gas barrier properties despite being a paper substrate, and that can maintain good gas barrier properties even after bending. [Brief explanation of the drawing]

[0009] [Figure 1] This diagram shows a vertically constructed, filled, and sealed bag. [Modes for carrying out the invention]

[0010] The following description is based on an example of an embodiment of the present invention (which may be referred to as "this embodiment"). However, the embodiments shown below are illustrative examples for embodying the technical concept of the present invention, and the present invention is not limited to the following description. Furthermore, while preferred embodiments are shown in this specification, combinations of two or more individual preferred embodiments are also preferred embodiments. If there are several numerical ranges for an item indicated by a numerical range, a preferred embodiment can be created by selectively combining the lower and upper limits of those ranges. In this specification, when a numerical range "QQ~RR" is mentioned, it means "QQ or greater and RR or less".

[0011] <Multilayer structure> The multilayer structure of the present invention comprises a paper layer (A) and a modified ethylene-vinyl alcohol layer (E) (hereinafter sometimes abbreviated as "modified EVOH layer (E)") made of a modified ethylene-vinyl alcohol copolymer (e) (hereinafter sometimes abbreviated as "modified EVOH (e)") described later.

[0012] The multilayer structure of the present invention may consist only of a paper layer (A) and a modified EVOH layer (E), or it may have other layers other than the paper layer (A) and modified EVOH layer (E) described later. From the viewpoint of not hindering the recyclability of paper, it is preferable that the modified EVOH layer (E) and the other layers are arranged on only one side of the paper layer (A). On the other hand, in order to provide good gas barrier properties, the modified EVOH layer (E) and the other layers may be arranged on both sides of the paper layer (A). The thickness of the modified EVOH (E) layer is usually 0.5 to 20 μm. In this specification, "gas barrier properties" can be evaluated based on the measured value of oxygen permeability, and specifically can be evaluated by the method described in the examples.

[0013] <Gas barrier properties> Gas barrier property is a function to prevent gas permeation. For example, it is the oxygen transmission rate (OTR) measured in accordance with JIS-K7126-2 (2006), Part 2 (isobaric method) under the conditions of 20 °C and 65% RH. Here, the oxygen transmission rate of "20 cc / (m 2 ·day·atm)" means that the oxygen permeation amount per unit area of the multilayer structure per day is 20 cc under 1 atm. If the gas barrier property is below the above upper limit, the preservation property of the contents is improved when the multilayer structure is used as a package. The upper limit of the oxygen transmission rate is preferably 20 cc / m 2 ·day·atm or less, more preferably 10 cc / m 2 ·day·atm or less, still more preferably 5 cc / m 2 ·day·atm or less, and most preferably 1 cc / m 2 ·day·atm. When the oxygen transmission rate is 20 cc / m 2 ·day·atm or less, the oxidative deterioration of the contents is suppressed when the contents are stored, and the preservation property is improved.

[0014] <Gas barrier property before and after folding> When processing the multilayer structure to produce a package, the multilayer structure may be folded. In the case of a multilayer structure provided with a paper layer (A), excessive stress is applied to the folded portion, so cracks may occur in other layers, resulting in a decrease in gas barrier property and deterioration of the contents when the contents are stored. Therefore, a package including a folded portion folded 360 degrees is produced, a part is cut out so that the folded portion is at the center, the oxygen transmission rate is measured, and the obtained value is designated as OTR2. A part without a folded portion is cut out, the oxygen transmission rate is measured, and when the obtained value is designated as gas barrier property OTR1, the upper limit of the ratio OTR2 / OTR1 of OTR2 and OTR1 is preferably less than 10, more preferably less than 5, and still more preferably less than 3.

[0015] <Heat seal strength> Good heat seal strength enhances the airtightness of the packaging, protecting the contents from oxidation by oxygen and deterioration due to moisture, thus extending the shelf life. For example, the heat seal strength at a width of 15 mm is measured in accordance with JIS Z 0238. A heat seal strength of 300 gf / 15 mm or higher is preferable, 500 gf / 15 mm or higher is more preferable, 800 gf / 15 mm or higher is even more preferable, and 1500 gf / 15 mm or higher is particularly preferable. If the strength is above the above levels, the airtightness of the contents can be enhanced, damage to the packaging during logistics can be reduced, and the shelf life can be extended.

[0016] <Paper layer (A)> The paper substrate may be a film or sheet containing, for example, pulp, fillers, chemicals, and pigments. Examples of pulp include chemical pulps such as bleached hardwood kraft pulp (LBKP), bleached softwood kraft pulp (NBKP), unbleached hardwood kraft pulp (LUKP), unbleached softwood pulp (NUKP), and sulfite pulp; mechanical pulps such as stone-ground pulp and thermomechanical pulp; wood fibers such as deinked pulp and recycled paper pulp; and non-wood fibers obtained from kenaf, bamboo, hemp, etc. These pulps can be used individually or in combination of two or more. Among these, chemical pulps, mechanical pulps, and wood fibers are preferred, with chemical pulps being more preferred, from the viewpoint of easily suppressing the occurrence of foreign matter contamination in the base paper and the occurrence of discoloration over time when recycling paper containers after use, and from the viewpoint of easily producing a good surface texture when printed.

[0017] Examples of fillers include known fillers such as white carbon, talc, kaolin, clay, heavy calcium carbonate, light calcium carbonate, titanium dioxide, zeolite, and synthetic resin fillers. Fillers can be used alone or in combination of two or more. Examples of chemicals include oxidized starch, hydroxyethyl etherified starch, enzyme-modified starch, polyacrylamide, polyvinyl alcohol, surface sizing agents (e.g., neutral sizing agents), water-resistant agents, water-retaining agents, thickeners, lubricants, yield improvers, water-draining agents, and paper strength enhancers, which can be used alone or in combination of two or more. Examples of yield improvers include aluminum sulfate and various anionic, cationic, nonionic, or amphoteric compounds. Examples of dry paper strength enhancers include polyacrylamide and cationic starch, and examples of wet paper strength enhancers include polyamidoamine epichlorohydrin. These chemicals are added within a range that does not affect the form or operability. Examples of neutral sizing agents include alkyl ketene dimers, alkenyl succinic anhydride, and neutral rosin sizing agents. Examples of pigments include inorganic pigments such as kaolin, clay, engineered kaolin, delaminated clay, heavy calcium carbonate, light calcium carbonate, mica, talc, titanium dioxide, barium sulfate, calcium sulfate, zinc oxide, silicic acid, silicates, colloidal silica, and satin white, as well as organic pigments such as solid, hollow, or core-shell types, which can be used individually or in combination of two or more. Furthermore, dyes, fluorescent whitening agents, pH adjusters, defoamers, pitch control agents, slime control agents, etc., can be added as needed. The surface of the paper substrate may also be treated with various chemicals and pigments.

[0018] The method for manufacturing paper substrates (papermaking) is not particularly limited, and paper substrates can be manufactured by papermaking using known methods such as acidic papermaking, neutral papermaking, and alkaline papermaking, using known screen formers, on-top hybrid formers, gap former machines, etc.

[0019] The method for surface treatment of the paper substrate is not particularly limited, but known coating equipment such as rod metering size presses, pound-type size presses, gate roll coaters, spray coaters, blade coaters, and curtain coaters can be used.

[0020] Examples of paper substrates (base paper) obtained in this manner include various known types such as fine paper, medium-quality paper, coated paper, glossy paper, kraft paper, glossy kraft paper, bleached kraft paper, unbleached kraft paper, rayon paper, tissue paper, glassine paper, cardboard, white cardboard, cellophane, and liner paper.

[0021] The paper substrate may have a transparent coating layer on one or both sides of the base paper as part of the paper substrate. Applying a transparent coating to the base paper makes it easier to improve the surface strength and smoothness of the base paper, and also improves the coatability when applying pigments. The transparent coating layer may contain a starch-derived polymer compound as a binder. The amount of transparent coating is 0.1 to 4.0 g / m² per side in terms of solid content. 2 Preferably, 0.5 to 2.5 g / m 2 More preferably, a coating solution mainly composed of various starches such as starch, oxidized starch, polyacrylamide, and polyvinyl alcohol may be applied to the base paper using a coater (coating machine) such as a size press, gate roll coater, pre-metalling size press, curtain coater, or spray coater. Furthermore, it is preferable to pre-calender the base paper before coating using an online soft calender or online chilled calender to smooth the base paper in advance, in order to make the coating layer after coating uniform.

[0022] The paper substrate may be smoothed as needed. For smoothing, standard smoothing devices such as supercalenders, gloss calenders, soft calenders, thermal calenders, and shoe calenders can be used. The smoothing devices are used as appropriate on-machine or off-machine, and the configuration of the pressurizing device, the number of pressurizing nips, and heating are adjusted as appropriate.

[0023] The basis weight of the paper substrate can be appropriately selected depending on the various qualities and handling requirements for the packaging, but it is typically 15-800 g / m². 2 A certain degree is preferable. For packaging materials used for packaging purposes, such as food packaging, bags, paper containers, cardboard boxes, and cups, 25-600 g / m² is preferred. 2 Those with the following properties are more preferable. Furthermore, for bags or flexible packaging as described later, 30-150 g / m² is preferred. 2 For paper packaging, the range is 170-600 g / m². 2 For cardboard, the liner material is 150-300g / m². 2 For the core material, use 120-200g / m². 2 Those with the above characteristics are particularly preferred. If the value is below the upper limit, the heat seal strength improves. If the value is above the lower limit, the mechanical strength improves, and problems during packaging manufacturing are reduced.

[0024] <Modified EVOH(e)> In the present invention, modified EVOH(e) is The material contains structural units (Ia), (Ib), and (Ic), and the respective content (mol%) of each structural unit (Ia), (Ib), and (Ic) a, b, and c satisfy the following formulas (1) to (3), and the degree of saponification (DS) of the modified ethylene-vinyl alcohol copolymer (e) represented by the following formula (4) is 90 mol% or more.

[0025] [ka]

[0026] In formula (I), a, b, and c are the content (mol%) of each monomer unit relative to 100 mol% of the total monomer units, and W is a methyl group or R 2 -OY represents a group, where X, Y, and Z each independently represent a hydrogen atom, a formyl group, or an alkanoyl group with 2 to 10 carbon atoms, and R 1 R represents a single bond, an alkylene group having 1 to 9 carbon atoms, or an alkylene oxy group having 1 to 9 carbon atoms. The alkylene group and the alkylene oxy group may contain a hydroxyl group, an alkoxy group, or a halogen atom. 2* represents an alkylene group having 1 to 9 carbon atoms or an alkylene oxy group having 1 to 9 carbon atoms, and the alkylene group and the alkylene oxy group may contain a hydroxyl group, an alkoxy group, or a halogen atom. * represents a bonding site.

[0027] In the present invention, modified EVOH(e) includes structural units (Ia), (Ib), and (Ic) represented by the above formula, and the respective content (mol%) of each structural unit (Ia), (Ib), and (Ic) a, b, and c satisfy the following formulas (1) to (3). 21 ≤ a ≤ 55 (1) 0.1 ≤ c ≤ 10 (2) [100-(a+c)]×0.9≦b≦[100-(a+c)] (3)

[0028] In the present invention, the degree of saponification (DS) of modified EVOH(e) is represented by the following formula (4), and the degree of saponification (DS) is 90 mol% or more. DS = [(Total number of moles of hydrogen atoms among X, Y, and Z) / (Total number of moles of X, Y, and Z)] × 100 (4)

[0029] The modified EVOH(e) used in this invention has units with quaternary carbon atoms in the main chain, in addition to ethylene units and vinyl alcohol units. The quaternary carbon atoms in the main chain have the effect of inhibiting crystallization due to steric hindrance and also enhance the stability of the solution state. Furthermore, because modified EVOH(e) has primary hydroxyl groups, it exhibits high gas barrier properties due to strong hydrogen bonding. Therefore, by using a coating agent containing modified EVOH(e), it is possible to enhance the gas barrier properties of the film formed after coating while maintaining high solution stability.

[0030] In equation (Ic), R 1 R represents a single bond, an alkylene group having 1 to 9 carbon atoms, or an alkylene oxy group having 1 to 9 carbon atoms, and the alkylene group and the alkylene oxy group may contain a hydroxyl group, an alkoxy group, or a halogen atom. 1It is preferable that the bond is a single bond. The number of carbon atoms in the alkylene group is preferably 5 or less, more preferably 3 or less, and even more preferably 2 or less. The number of carbon atoms in the alkylene oxy group is preferably 5 or less, more preferably 3 or less, and even more preferably 2 or less.

[0031] In formula (Ic), W is a methyl group or R 2 -OY represents a group, where Y and Z independently represent a hydrogen atom, a formyl group, or an alkanoyl group having 2 to 10 carbon atoms. W is a methyl group or R from the viewpoint of improving the stability of the solution and gas barrier properties. 2 It is preferable that the group is represented by -OH (i.e., Y is a hydrogen atom), R 2 It is preferable that the group is represented by -OH (i.e., Y is a hydrogen atom) and that Z is a hydrogen atom. 2 Among the groups represented by -OH, R 2 The group is preferably an alkylene group, more preferably an ethylene group or a methylene group, and even more preferably a methylene group.

[0032] In equation (Ic), R 2 R represents an alkylene group having 1 to 9 carbon atoms or an alkylene oxy group having 1 to 9 carbon atoms, and the alkylene group and the alkylene oxy group may contain a hydroxyl group, an alkoxy group, or a halogen atom. 2 It is preferable that the alkylene group is the aforementioned alkylene group. The number of carbon atoms in the alkylene group is preferably 5 or less, more preferably 3 or less, and even more preferably 2 or less. The number of carbon atoms in the alkylene oxy group is preferably 5 or less, more preferably 3 or less, and even more preferably 2 or less.

[0033] In formulas (Ib) and (Ic), if X, Y, or Z is a hydrogen atom, modified EVOH(e) has a hydroxyl group, and if X, Y, or Z is a formyl group or an alkanoyl group, modified EVOH(e) has an ester group. The alkanoyl group is preferably an alkanoyl group having 2 to 5 carbon atoms, with acetyl groups, propanoyl groups, and butanoyl groups being more preferred, and acetyl groups being even more preferred. It is preferable that X, Y, and Z are all hydrogen atoms or mixtures containing hydrogen atoms.

[0034] Examples of the above formula (Ic) include structural units represented by the following formulas (IIc) and (IIIc), with the structural unit represented by formula (IIc) being preferred. In the formulas, * represents a binding site.

[0035] [ka]

[0036] [ka]

[0037] In formula (IIc), R 3 and R 4 Each of these independently represents a hydrogen atom or an alkyl group having 1 to 8 carbon atoms, and the alkyl group may contain a hydroxyl group, an alkoxy group, or a halogen atom.

[0038] In the present invention, from the viewpoint of improving gas barrier properties, in formula (IIc), R 3 and R 4 It is preferable that it is a hydrogen atom.

[0039] In modified EVOH(e), a represents the content (mol%) of (Ia) relative to the total monomer units, and is between 21 and 55 mol% (Equation (1)). If a is less than 21 mol%, the thermal stability during melt-kneading and recycling decreases, and gels and lumps are more likely to occur. a is preferably 26 mol% or more, and more preferably 30 mol% or more. On the other hand, if a exceeds 55 mol%, the gas barrier properties of modified EVOH(e) at low humidity (e.g., 65% humidity) become insufficient. a is preferably 52 mol% or less, and more preferably 46 mol% or less.

[0040] In modified EVOH(e), c represents the content (mol%) of (Ic) relative to the total monomer units, and is between 0.1 and 10 mol% (Equation (2)). If c is less than 0.1 mol%, the solution stability of modified EVOH(e) becomes insufficient. c is preferably 0.3 mol% or more, more preferably 0.5 mol% or more, even more preferably 0.8 mol% or more, and particularly preferably 1.0 mol% or more. On the other hand, if c exceeds 10 mol%, the strength of the film decreases. c is preferably 5 mol% or less, and may also be preferably 4 mol% or less, 3 mol% or less, 2 mol% or less, 1.8 mol% or less, or less than 1.2 mol%.

[0041] In modified EVOH(e), b represents the content (mol%) of (Ib) relative to the total monomer units, and b satisfies formula (3). If b does not satisfy formula (3), the gas barrier properties of the coating after application are insufficient. Preferably, b satisfies the following formula (3'), and more preferably, it satisfies the following formula (3”). In formula (Ib), if X is two or more functional groups selected from the group consisting of a hydrogen atom, a formyl group, and an alkanoyl group having 2 to 10 carbon atoms (i.e., if it contains both vinyl alcohol units and vinyl ester units), then b is their sum. [100-(a+c)]×0.95≦b≦[100-(a+c)](3') [100-(a+c)]×0.98≦b≦[100-(a+c)](3”)

[0042] In modified EVOH(e), the degree of saponification (DS) is defined by equation (4), and the degree of saponification (DS) is 90 mol% or higher. Here, "total number of moles of hydrogen atoms among X, Y, and Z" indicates the number of moles of hydroxyl groups, and "total number of moles of X, Y, and Z" indicates the total number of moles of hydroxyl groups and ester groups. If the degree of saponification (DS) is less than 90 mol%, sufficient barrier performance cannot be obtained, the thermal stability of the modified EVOH(e) becomes insufficient, and gels and lumps are more likely to be generated when it is melt-kneaded and recycled. In addition, the decrease in thermal stability tends to reduce the long-run moldability during high-temperature molding. The degree of saponification (DS) is preferably 95 mol% or more, more preferably 98 mol% or more, and even more preferably 99 mol% or more. In particular, to have excellent barrier properties and thermal stability, the degree of saponification (DS) is preferably 99 mol% or more, more preferably 99.5 mol% or more, and even more preferably 99.8 mol% or more. The degree of saponification (DS) is usually 100 mol% or less.

[0043] The degree of saponification (DS) can be obtained by nuclear magnetic resonance (NMR) spectroscopy. The content of monomer units indicated by a, b, and c above can also be obtained by NMR spectroscopy. Furthermore, the modified EVOH(e) used in this invention is usually a random copolymer. The random copolymer nature can be confirmed by NMR and melting point measurements.

[0044] The preferred melt flow rate (MFR) of modified EVOH(e) (at 190°C under a 2160g load) is 0.1 to 30 g / 10 min, more preferably 0.3 to 25 g / 10 min, and even more preferably 0.5 to 20 g / 10 min. However, for materials with a melting point around or above 190°C, measurements are taken under a 2160g load at multiple temperatures above the melting point. The reciprocal of the absolute temperature is plotted on the x-axis and the logarithm of the MFR on the y-axis of a semi-logarithmic graph, and the value is expressed by extrapolating to 190°C. If the MFR is less than 0.1 g / 10 min, the viscosity of the solution is too high relative to the solid content concentration, making it impossible to apply the required thickness of the coating in one application. This results in insufficient gas barrier properties or the need for multiple applications, leading to reduced productivity. If the MFR exceeds 30g / 10min, the viscosity of the solution is too low relative to the solid content concentration. As a result, even a slight difference in viscosity between solutions can cause a large change in the thickness of the coating, making it impossible to provide stable gas barrier properties to the packaging material.

[0045] Modified EVOH(e) may be a mixture with unmodified EVOH. From the viewpoint of reducing costs, the mass ratio of modified EVOH(e) to unmodified EVOH in the mixture (modified EVOH(e) / unmodified EVOH) is preferably 1 / 9 to 9 / 1. On the other hand, from the viewpoint of more significantly exhibiting the effects of the present invention, the mass ratio (modified EVOH(e) / unmodified EVOH) is preferably greater than 9 / 1, and it is even more preferable that the mixture substantially does not contain unmodified EVOH.

[0046] When the modified EVOH(e) is a mixture of two or more different types of modified EVOH or a mixture of the modified EVOH(e) and the unmodified EVOH, the average value calculated from the blending mass ratio is used as the content, degree of saponification, and MFR of each monomer unit.

[0047] <Method for producing modified EVOH(e)> Next, the production of modified EVOH(e) will be described. The method for producing modified EVOH(e) is not particularly limited, and one example is to radically polymerize ethylene, a vinyl ester represented by the following formula (V), and an unsaturated monomer represented by the following formula (VI) to obtain a modified ethylene-vinyl ester copolymer having structural units represented by the following formulas (VIIa), (VIIb), and (VIIc), and then saponify it. In formulas (VIIa), (VIIb), and (VIIc), a, b, and c represent the content (mol%) of ethylene units, vinyl ester units, and units derived from the unsaturated monomer represented by the following formula (VI), respectively, relative to the total monomer units.

[0048] [ka]

[0049] [ka]

[0050] [ka]

[0051] In formula (V), R 5 The '' represents a hydrogen atom or an alkyl group having 1 to 9 carbon atoms. The number of carbon atoms in the alkyl group is preferably 1 to 4. Examples of vinyl esters represented by formula (V) include vinyl formate, vinyl acetate, vinyl propionate, vinyl butyrate, vinyl isobutyrate, vinyl pivalate, vinyl versatate, and vinyl caproate. From an economic standpoint, vinyl acetate is more preferred.

[0052] In formula (VI), R 3 and R 4 This is the same as equation (IIc) above. R 6 and R 7Each of these independently represents a hydrogen atom or an alkyl group having 1 to 9 carbon atoms. Examples of unsaturated monomers represented by formula (VI) include 2-methylene-1,3-propanediol diacetate, 2-methylene-1,3-propanediol dipropionate, and 2-methylene-1,3-propanediol dibutyrate. Among these, 2-methylene-1,3-propanediol diacetate is preferred due to its ease of manufacture. In the case of 2-methylene-1,3-propanediol diacetate, R 3 and R 4 is a hydrogen atom, and R 6 and R 7 This is a methyl group.

[0053] Modified EVOH(e) may contain structural units derived from ethylene, vinyl esters represented by formula (V), and other ethylenically unsaturated monomers copolymerizable with unsaturated monomers represented by formula (VI), to the extent that the effects of the present invention are not inhibited. Such other ethylenically unsaturated monomers include, for example, α-olefins such as propylene, n-butene, isobutylene, and 1-hexene; acrylic acid and its salts; unsaturated monomers having acrylic acid ester groups; methacrylic acid and its salts; unsaturated monomers having methacrylic acid ester groups; acrylamide, N-methylacrylamide, N-ethylacrylamide, N,N-dimethylacrylamide, diacetoneacrylamide, acrylamidopropanesulfonic acid and its salts, acrylamidopropyldimethylamine and its salts (e.g., quaternary salts); methacrylamide, N-methylmethacrylamide, N-ethylmethacrylamide, methacrylamidopropanesulfonic acid and its salts, methacrylamidopropyldimethylamine and its salts (e.g., quaternary salts); methyl vinyl ether, Examples include vinyl ethers such as ethyl 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.

[0054] Furthermore, instead of the unsaturated monomer represented by formula (VI) above, an unsaturated monomer represented by the following formula (VIII) may be copolymerized.

[0055] [ka]

[0056] In formula (VIII), R 3 and R 4 This is the same as formula (IIc). Examples of unsaturated monomers represented by formula (VIII) include 2-methylene-1,3-propanediol and 2-methylene-1,3-butanediol.

[0057] The unsaturated monomers represented by formulas (VI) and (VIII) exhibit high copolymerization reactivity with vinyl ester monomers, thus facilitating copolymerization. Therefore, it is easy to achieve a high degree of modification and polymerization in the resulting modified ethylene-vinyl ester copolymer. Furthermore, even if the polymerization reaction is stopped at a low polymerization rate, the amount of unreacted unsaturated monomer remaining at the end of polymerization is small, making it superior in terms of environmental impact and cost. In this respect, the unsaturated monomers represented by formulas (VI) and (VIII) are superior to other monomers with only one carbon atom having a functional group at the allyl position, such as allyl glycidyl ether and 3,4-diacetoxy-1-butene. Here, the unsaturated monomer represented by formula (VI) is more reactive than the unsaturated monomer represented by formula (V).

[0058] When copolymerizing ethylene, a vinyl ester represented by formula (V), and an unsaturated monomer represented by formula (VI) or (VIII) to produce a modified ethylene-vinyl ester copolymer, the polymerization method may be batch polymerization, semi-batch polymerization, continuous polymerization, or semi-continuous polymerization. Furthermore, known polymerization methods such as bulk polymerization, solution polymerization, suspension polymerization, and emulsion polymerization can be employed. Bulk polymerization or solution polymerization, which proceed in a solvent-free environment or in a solvent such as alcohol, are commonly used. When obtaining a modified ethylene-vinyl ester copolymer with a high degree of polymerization, emulsion polymerization is one option.

[0059] The solvent used in solution polymerization is not particularly limited, but examples include alcohols, with lower alcohols such as methanol, ethanol, and propanol being more preferred. The amount of solvent used in the polymerization reaction solution should be selected considering the viscosity-average degree of polymerization of the target modified EVOH(e) and the chain transfer of the solvent. The mass ratio of the solvent to the total monomers in the reaction solution (solvent / total monomers) is usually in the range of 0.01 to 10, preferably in the range of 0.03 to 3, and more preferably in the range of 0.05 to 1.

[0060] The polymerization initiator used when copolymerizing ethylene with a vinyl ester represented by formula (V) and an unsaturated monomer represented by formula (VI) or (VIII) is selected from known polymerization initiators, such as azo initiators, peroxide initiators, and redox initiators, depending on the polymerization method. Examples of azo initiators include 2,2'-azobisisobutyronitrile, 2,2'-azobis(2,4-dimethylvaleronitrile), and 2,2'-azobis(4-methoxy-2,4-dimethylvaleronitrile). Examples of peroxide-based initiators include peroxide compounds such as diisopropyl peroxydicarbonate, di-2-ethylhexyl peroxydicarbonate, and diethoxyethyl peroxydicarbonate; perester compounds such as t-butyl peroxyneodecanate, α-cumyl peroxyneodecanate, and acetyl peroxide; acetylcyclohexyl sulfonyl peroxide; and 2,4,4-trimethylpentyl-2-peroxyphenoxyacetate. Potassium persulfate, ammonium persulfate, and hydrogen peroxide may be combined with the initiators. Redox initiators are polymerization initiators that combine the above peroxide-based initiators with reducing agents such as sodium bisulfite, sodium bicarbonate, tartaric acid, L-ascorbic acid, and longalit. The amount of polymerization initiator used is adjusted according to the polymerization rate. The amount of polymerization initiator used is preferably 0.01 to 0.2 mol, and more preferably 0.02 to 0.15 mol, per 100 mol of vinyl ester monomer. The polymerization temperature is not particularly limited, but a range of room temperature to about 150°C is appropriate, and preferably it is between 40°C and 100°C.

[0061] When copolymerizing ethylene, a vinyl ester represented by formula (V), and an unsaturated monomer represented by formula (VI) or (VIII), copolymerization may be carried out in the presence of a chain transfer agent, provided that the effects of the present invention are not inhibited. Examples of chain transfer agents include aldehydes such as acetaldehyde and propionaldehyde; ketones such as acetone and methyl ethyl ketone; mercaptans such as 2-hydroxyethanethiol; and phosphinates such as sodium phosphinate monohydrate. Among these, aldehydes and ketones are preferred. The amount of chain transfer agent added to the polymerization reaction solution is determined according to the chain transfer coefficient of the chain transfer agent and the degree of polymerization of the desired modified ethylene-vinyl ester copolymer, but generally, 0.1 to 10 parts by mass per 100 parts by mass of vinyl ester monomer is preferred.

[0062] Polymerization is carried out for a predetermined time, and after reaching a predetermined polymerization rate, a polymerization inhibitor is added as needed, and unreacted ethylene gas is evaporated and removed, followed by the expulsion of unreacted vinyl esters and unsaturated monomers represented by formulas (VI) or (VIII). As a method for expelling these, for example, a polymerization solution from which ethylene has been removed is continuously supplied at a constant rate from the top of a column packed with Raschig rings, and an organic solvent vapor, preferably an alcohol with a boiling point of 100°C or less, and optimally methanol vapor, is blown in from the bottom of the column, and a mixed vapor of the organic solvent and unreacted vinyl esters, etc. is distilled from the top of the column, and the copolymer solution from which the unreacted vinyl esters, etc. have been removed is taken out from the bottom of the column.

[0063] An alkaline catalyst is added to the copolymer solution from which unreacted vinyl esters and other components have been removed, and the vinyl ester components in the copolymer are saponified. Both continuous and batch saponification methods are possible. Sodium hydroxide, potassium hydroxide, alkali metal alkoxides, etc., can be used as alkaline catalysts. Methanol is preferred as the solvent for saponification. For example, the saponification conditions are as follows: (1) Concentration of ethylene-vinyl ester copolymer in solution: 10-50% by mass (2) Reaction temperature: 30-150°C (3) Catalyst usage: 0.005 to 0.6 equivalents (per vinyl ester component) (4) Time (for continuous type, average dwell time); 10 minutes to 6 hours

[0064] Generally, continuous saponification allows for more efficient removal of methyl acetate produced by saponification, thus enabling the acquisition of resins with a higher degree of saponification using a smaller amount of catalyst compared to batch saponification. Furthermore, in continuous saponification, a higher temperature is required to prevent the precipitation of EVOH produced by saponification. Therefore, in continuous saponification, the reaction temperature and catalyst amount are preferably within the following ranges. Reaction temperature: 70-150°C Catalyst usage: 0.005 to 0.1 equivalents (per vinyl ester component)

[0065] By saponifying the modified ethylene-vinyl ester copolymer in this way, a solution or paste containing modified EVOH(e) is obtained. At this time, the vinyl ester units in the copolymer are converted to vinyl alcohol units. In addition, the ester bonds derived from the unsaturated monomer shown in formula (VI) are simultaneously hydrolyzed and converted to a 1,3-diol structure. Thus, different types of ester groups can be hydrolyzed simultaneously in a single saponification reaction.

[0066] The modified EVOH(e) after the saponification reaction contains alkaline catalysts, by-product salts such as sodium acetate and potassium acetate, and other impurities, so these may be removed by neutralization and washing as needed. Here, when washing the modified EVOH(e) after the saponification reaction with ion-exchanged water that contains almost no metal ions, chloride ions, etc., some catalyst residue such as sodium acetate and potassium acetate may remain in the modified EVOH(e).

[0067] The EVOH solution or paste obtained by the saponification reaction typically contains 50 parts by mass or more of alcohol per 100 parts by mass of EVOH. The alcohol is preferably methanol.

[0068] The method for washing the EVOH solution or paste and adjusting its water content is not particularly limited, but can be carried out as follows: While heating and stirring the EVOH solution or paste, water is added to distill off the alcohol and precipitate modified EVOH(e). The temperature at this time is preferably 50 to 100°C. The precipitated modified EVOH(e) is washed with water or an aqueous acetic acid solution. The temperature at this time is preferably 5 to 50°C. The modified EVOH(e) after washing is dried as needed. For example, it is dried at 50 to 100°C for 1 to 24 hours. The water content of the modified EVOH(e) can be adjusted by the washing and drying conditions at this time.

[0069] <Other components contained in denatured EVOH(e)> It is preferable that the modified EVOH(e) contains alkali metal ions. By including alkali metal ions in the modified EVOH(e), the adhesion between adjacent layers can be improved when a multilayer structure is formed, and as a result, the gas barrier properties can be maintained before and after bending.

[0070] The lower limit of the alkali metal ion content (content in the dry resin composition) is preferably 2.5 μmol / g, more preferably 3.5 μmol / g, and even more preferably 4.5 μmol / g. On the other hand, the upper limit of this content is preferably 22 μmol / g, more preferably 16 μmol / g, and even more preferably 10 μmol / g. If the metal ion content is greater than the lower limit, interlayer adhesion is enhanced, and gas barrier properties can be maintained before and after bending. On the other hand, if the alkali metal ion content is less than the upper limit, gel generation during melt extrusion can be suppressed.

[0071] Examples of alkali metal ions include lithium, sodium, potassium, rubidium, and cesium, but sodium or potassium ions are more preferred from the standpoint of industrial availability.

[0072] The alkali metal salts that provide alkali metal ions are not particularly limited, but examples include aliphatic carboxylates, aromatic carboxylates, phosphates, and metal complexes of lithium, sodium, and potassium. Specifically, examples of these alkali metal salts include sodium acetate, potassium acetate, sodium phosphate, lithium phosphate, sodium stearate, potassium stearate, and sodium salts of ethylenediaminetetraacetic acid. Among these, sodium acetate, potassium acetate, and sodium phosphate are particularly preferred due to their readily available availability.

[0073] It is also preferable that the modified EVOH(e) contains alkaline earth metal ions. Examples of alkaline earth metal ions include beryllium, magnesium, calcium, strontium, and barium, but from the standpoint of industrial availability, magnesium or calcium ions are more preferable. The inclusion of alkaline earth metal ions in the modified EVOH(e) reduces defects such as gels and lumps, and improves recyclability.

[0074] Furthermore, EVOH blended with boron compounds can also be used as modified EVOH(e). Examples of boron compounds include boric acid, boric acid esters, borate salts, and boron hydride compounds. Specifically, examples of boric acid include orthoboric acid, metaboric acid, and tetraboric acid; examples of boric acid esters include triethyl borate and trimethyl borate; and examples of borate salts include alkali metal salts, alkaline earth metal salts, and borax of the aforementioned boric acid compounds. Among these compounds, orthoboric acid (hereinafter sometimes simply referred to as boric acid) is preferred.

[0075] When using EVOH(e) blended with boron compounds as modified EVOH(e), the boron compound content is preferably 20 to 2000 ppm, more preferably 50 to 1000 ppm, in terms of elemental boron. Blending boron compounds within this range may further improve the standing stability of the solution.

[0076] Furthermore, modified EVOH(e) containing a phosphate compound may be used as the modified EVOH(e). This may help stabilize the quality of the resin (coloring, etc.). The phosphate compound used in the present invention is not particularly limited, and various acids such as phosphoric acid and phosphorous acid, or their salts, can be used. The phosphate may be included in the form of monophosphate, dicate, or tertiary phosphate, but monophosphate is preferred. The cation species is also not particularly limited, but alkali metal salts are preferred. Among these, sodium dihydrogen phosphate and potassium dihydrogen phosphate are preferred. When using modified EVOH(e) containing a phosphate compound, the content of the phosphate compound is preferably 200 ppm or less in terms of phosphate root, more preferably 5 to 100 ppm, and optimally 5 to 50 ppm.

[0077] Furthermore, within the limits that do not hinder the objectives of the present invention, modified EVOH(e) can also be used that contains a heat stabilizer, an antioxidant, and inorganic fine particles.

[0078] Among inorganic fine particles, amorphous silica is preferred because it exhibits an antiblocking effect and improves the gas barrier properties of modified EVOH(e). The amount of inorganic fine particles added is preferably 10 to 10,000 ppm, more preferably 100 to 3,000 ppm, and optimally 500 to 1,500 ppm.

[0079] <Other layers> The multilayer structure of the present invention preferably comprises an intermediate layer (F) and a sealant layer (G) as other layers. When an intermediate layer (F) is provided, it is preferable that it is directly laminated to the paper layer (A) and that the modified EVOH layer (E) is directly laminated to the intermediate layer (F) in order to suppress the decrease in gas barrier properties after bending. When a sealant layer (G) is provided, it is preferable that it is placed on the outermost layer side in order to improve the heat seal strength of the multilayer structure. Here, " / " means that it is laminated directly, and " / / " means that it is laminated via an adhesive layer. Paper layer (A) / Modified EVOH layer (E), Modified EVOH layer (E) / Paper layer (A) / Modified EVOH layer (E), Modified EVOH layer (E) / Paper layer (A) / Modified EVOH layer (E) / Paper layer (A) / Modified EVOH layer (E), Paper layer (A) / Intermediate layer (F) / Modified EVOH layer (E) Paper layer (A) / Intermediate layer (F) / Modified EVOH layer (E) / Sealant layer (G) Paper layer (A) / Intermediate layer (F) / Modified EVOH layer (E) / Sealant layer (G) Modified EVOH layer (E) / Intermediate layer (F) / Paper layer (A) / Modified EVOH layer (E) / Paper layer (A) / Modified EVOH layer (E), Modified EVOH layer (E) / Intermediate layer (F) / Paper layer (A) / Modified EVOH layer (E) / Paper layer (A) / Modified EVOH layer (E) / Sealant layer (G), Modified EVOH layer (E) / Intermediate layer (F) / Paper layer (A) / Modified EVOH layer (E) / Paper layer (A) / Modified EVOH layer (E) / / Sealant layer (G), Modified EVOH layer (E) / Intermediate layer (F) / Paper layer (A) / Intermediate layer (F) / Modified EVOH layer (E) / Paper layer (A) / Modified EVOH layer (E), Modified EVOH layer (E) / Intermediate layer (F) / Paper layer (A) / Intermediate layer (F) / Modified EVOH layer (E) / Paper layer (A) / Modified EVOH layer (E) / Sealant layer (G), Modified EVOH layer (E) / Intermediate layer (F) / Paper layer (A) / Intermediate layer (F) / Modified EVOH layer (E) / Paper layer (A) / Modified EVOH layer (E) / / Sealant layer (G) Modified EVOH layer (E) / Intermediate layer (F) / Paper layer (A) / Intermediate layer (F) / Modified EVOH layer (E) / Paper layer (A) / Intermediate layer (F) / Modified EVOH layer (E), Modified EVOH layer (E) / Intermediate layer (F) / Paper layer (A) / Intermediate layer (F) / Modified EVOH layer (E) / Paper layer (A) / Intermediate layer (F) / Modified EVOH layer (E) / Sealant layer (G), Modified EVOH layer (E) / Intermediate layer (F) / Paper layer (A) / Intermediate layer (F) / Modified EVOH layer (E) / Paper layer (A) / Intermediate layer (F) / Modified EVOH layer (E) / / Sealant layer (G).

[0080] <Middle layer (F)> The intermediate layer (F) may be an anchor coat layer formed by applying and drying an anchor coat agent, or it may be a thermoplastic resin layer formed by melt extrusion.

[0081] As the anchor coating agent for the intermediate layer (F), any resin having a heat resistance temperature of 135°C or higher, such as vinyl-modified resin, epoxy resin, urethane resin, polyester resin, etc., can be used. In particular, an anchor coating agent consisting of a polyacrylic or polymethacrylic resin having two or more hydroxyl groups in its structure and an isocyanate compound as a curing agent can be preferably used. A silane coupling agent may also be used as an additive, and nitrated cotton may also be used to enhance heat resistance.

[0082] As the thermoplastic resin layer of the intermediate layer (F), it is preferable to use an adhesive resin containing a carboxylic acid-modified polyolefin that has adhesion to modified EVOH(e). As the carboxylic acid-modified polyolefin, a modified olefin polymer containing a carboxyl group obtained by chemically (e.g., addition reaction, graft reaction, etc.) bonding an ethylenically unsaturated carboxylic acid, its ester, or its anhydride to an olefin polymer can be suitably used. Here, examples of olefin polymers include polyethylene (e.g., low-density polyethylene, medium-density polyethylene, high-density polyethylene), linear low-density polyethylene, polypropylene, polybutene and other polyolefins, and copolymers of olefins with other monomers (e.g., vinyl esters, unsaturated carboxylic acid esters, etc.) (e.g., ethylene-vinyl acetate copolymer, ethylene-ethyl acrylate copolymer, etc.). Linear low-density polyethylene, ethylene-vinyl acetate copolymer (vinyl acetate content 5-55% by mass), and ethylene-ethyl acrylate copolymer (ethyl acrylate content 8-35% by mass) are preferred, and linear low-density polyethylene and ethylene-vinyl acetate copolymer are particularly preferred. Examples of ethylenically unsaturated carboxylic acids, their esters, or their anhydrides include ethylenically unsaturated monocarboxylic acids, their esters, ethylenically unsaturated dicarboxylic acids, their mono or diesters, or their anhydrides, with ethylenically unsaturated dicarboxylic acid anhydrides being preferred. Specific examples include maleic acid, fumaric acid, itaconic acid, maleic anhydride, itaconic anhydride, monomethyl maleic acid, monoethyl maleic acid, diethyl maleic acid, and monomethyl fumaric acid, with maleic anhydride being particularly preferred.

[0083] The amount of ethylenically unsaturated carboxylic acid or its anhydride added to or grafted onto the olefin polymer (degree of modification) is preferably, for example, 0.0001% to 15% by mass, and more preferably 0.001% to 10% by mass, relative to the olefin polymer. The addition reaction or graft reaction of ethylenically unsaturated carboxylic acid or its anhydride onto the olefin polymer can be carried out, for example, by radical polymerization in the presence of a solvent (such as xylene) and a catalyst (such as a peroxide). The melt flow rate (MFR, under a 2160g load) of the carboxylic acid-modified polyolefin obtained in this way, measured at 210°C, is preferably 0.2g / 10 min to 30g / 10 min, and more preferably 0.5g / 10 min to 10g / 10 min. These adhesive resins may be used individually or as a mixture of two or more.

[0084] In the present invention, the lower limit of the average thickness of the intermediate layer (F) is preferably 0.1 μm or more, more preferably 0.3 μm or more, and even more preferably 0.5 μm or more. If it is above the lower limit, the decrease in gas barrier properties after folding is suppressed. The upper limit of the average thickness is preferably 50 μm or less, more preferably 30 μm or less, and even more preferably 10 μm or less. If it is below the upper limit, the recyclability of the paper is improved.

[0085] <Sealant layer G> The sealant layer G may be a resin layer formed by applying a coating agent and drying it, or it may be a thermoplastic resin layer formed by melt extrusion.

[0086] The resin layer of the sealant layer G can be any resin with a heat resistance temperature of 135°C or higher, such as a coating agent made of vinyl-modified resin, epoxy resin, urethane resin, polyester resin, or polylactic acid (PLA) resin, styrene acrylic acid copolymer resin, polyolefin copolymer, or ethylene methacrylic acid copolymer. In particular, an anchor coating agent consisting of a polyacrylic or polymethacrylic resin having two or more hydroxyl groups in its structure and an isocyanate compound as a curing agent can be preferably used. A silane coupling agent may also be used as an additive, and nitrated cotton may also be used to enhance heat resistance.

[0087] The thermoplastic resin constituting the sealant layer (G) is not particularly limited as long as it is a resin that softens and exhibits plasticity when heated to its glass transition temperature or melting point. Examples include polyolefin resins (polyethylene resin, polypropylene resin, etc.), grafted polyolefin resins modified with unsaturated carboxylic acids or their esters, halogenated polyolefin resins, ethylene-vinyl acetate copolymer resins, ethylene-acrylic acid copolymer resins, ethylene-acrylic acid ester copolymer resins, polyester resins, polyamide resins, polyvinyl chloride resins, polyvinylidene chloride resins, acrylic resins, polystyrene resins, vinyl ester resins, ionomers, polyester elastomers, polyurethane elastomers, aromatic or aliphatic polyketones, etc. Polyolefin resins are particularly preferred due to their good mechanical strength and moldability, and polyethylene resins and polypropylene resins are more preferred.

[0088] The thermoplastic resin layer may contain additives to the extent that it does not impair the objectives of the present invention. Examples of additives include resins other than the thermoplastic resin, heat stabilizers, ultraviolet absorbers, antioxidants, colorants, fillers, etc. When the thermoplastic resin layer contains additives other than the thermoplastic resin, the content of the additives is preferably 20% by mass or less, more preferably 10% by mass or less, and even more preferably 5% by mass or less, relative to the total amount of the thermoplastic resin layer.

[0089] The thermoplastic resin layer contains a thermoplastic resin as its main component. The thermoplastic resin layer may contain either a single thermoplastic resin or a mixture of multiple thermoplastic resins as its main component.

[0090] The lower limit of the average thickness of the sealant layer (G) is preferably 1 μm or more, more preferably 3 μm or more, and even more preferably 5 μm or more. If it is above the lower limit, it will have good heat seal strength. The upper limit of the average thickness is preferably 100 μm or less, more preferably 50 μm or less, even more preferably 40 μm or less, and particularly preferably 30 μm or less. If it is below the upper limit, the recyclability of the paper will be improved.

[0091] When the weight of the paper layer (A) is M1 and the total weight of the other layers is M2, the lower limit of M1 / M2 is preferably 1.00 or more, more preferably 1.25 or more, even more preferably 2.33 or more, and particularly preferably 4.00 or more. If it is above the lower limit, the recyclability of the paper is improved. An example of a method for calculating M2 is to measure the thickness of each layer from the cross-section of the obtained multilayer structure, calculate the weight of each layer from the specific gravity of each layer, and obtain it by summing them up. The upper limit of M1 / M2 is preferably 300 or less, more preferably 100 or less, and even more preferably 50 or less. If it is below the upper limit, the stress at the bend when it is used as packaging is reduced, and the deterioration of gas barrier properties is suppressed.

[0092] <Method for manufacturing multilayer structures> In the present invention, examples of multilayering methods include solution coating methods (direct gravure roll coating method, gravure roll coating method, kiss coating method, reverse roll coating method, fontein method, transfer roll coating method), extrusion coating method, extrusion lamination method, film lamination method, and co-extrusion method, and multiple methods from among these can be used.

[0093] <Applications of multilayer structures> One of the applications of the multilayer structure of the present invention is a packaging body, which is one of the preferred embodiments. This packaging body may be composed solely of the multilayer structure of the present invention, or it may be composed of the multilayer structure and other components. The packaging body can be manufactured in various ways. For example, a container (packaging body) may be manufactured by joining a sheet-like multilayer structure or a film material containing the multilayer structure (hereinafter also simply referred to as "film material") and forming it into the shape of a predetermined container. The packaging body containing the multilayer structure of the present invention can be applied to various uses by taking advantage of its excellent gas barrier properties. This packaging body is preferably used in applications where gas barrier properties against oxygen are required, or in applications where the inside of the packaging body is replaced with various functional gases. For example, the packaging body according to the present invention is preferably used as a food packaging body. In addition to food packaging bodies, the packaging body according to the present invention is also preferably used as a packaging body for pharmaceuticals such as pesticides and medicines; medical equipment; industrial materials such as machine parts and precision materials; clothing, etc.

[0094] The multilayer structure of the present invention may be secondarily processed into various packaging materials. Such packaging materials may be vertically formed, filled, and sealed bags, pouches, vacuum packaging materials, cup-shaped containers, bags, container lids, or in-mold labels.

[0095] <Vertical-formed, filled, and sealed bags> The packaging body containing the multilayer structure of the present invention may be a vertically made, filled, and sealed bag. An example is shown in Figure 1. The vertically made, filled, and sealed bag 10 shown in Figure 1 is formed by sealing the multilayer structure 11 on three sides: two ends 11a and a body portion 11b. The vertically made, filled, and sealed bag 10 can be manufactured by a vertical bag-making and filling machine. Various methods can be applied to bag making using a vertical bag-making and filling machine, but in any method, the contents are supplied into the bag from an opening at the top, and then the opening is sealed to produce a vertically made, filled, and sealed bag. The vertically made, filled, and sealed bag is composed of, for example, a single film material that is heat-sealed on three sides: the top end, the bottom end, and the sides. The vertically made, filled, and sealed bag as a container according to the present invention has excellent gas barrier properties, and the barrier performance is maintained even after bag making, so the deterioration of the quality of the contents can be suppressed over a long period of time.

[0096] <Uses of packaging> The packaging containing the multilayer structure of the present invention has gas barrier properties, and when the contents of the packaging are food, the effect of preserving the quality of the contents can be further enhanced. Furthermore, in order to suppress the growth of microorganisms in the food and improve the shelf life of the food, the water activity of the food in the packaging is preferably 0.94 or less, more preferably 0.80 or less, and even more preferably 0.60 or less. On the other hand, since excessively lowering the water activity can reduce the taste and texture of the food, the water activity of the food is preferably 0.10 or higher. [Examples]

[0097] The present invention will be specifically described below with reference to examples, but the present invention is not limited in any way by these examples. The evaluation methods used in the following examples and comparative examples are shown below.

[0098] • Content of each structural unit in modified ethylene-vinyl acetate copolymer In modified ethylene-vinyl acetate copolymer (hereinafter sometimes referred to as modified EVAc), the ethylene unit content (a mol%) in formula (VIIa), the vinyl acetate unit content (b mol%) in formula (VIIb), and the content of structural units derived from the unsaturated monomer represented by formula (VI) (c mol%) in formula (VIIc) are as follows: 1 The values ​​were calculated by 1H-NMR measurement. A small sample of the MeOH solution of the synthesized modified EVAc 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 modified EVAc. Next, the obtained dried modified EVAc was dissolved in dimethyl sulfoxide (DMSO)-d6 containing tetramethylsilane as an internal standard, and analyzed at 500 MHz. 1 The measurement was performed at 80°C using 1H-NMR (JEOL Ltd.: "GX-500").

[0099] 2-Methylene-1,3-propanediol diacetate (In formula (VI), R 3 and R 4 R is a hydrogen atom, 6 and R 7 Modified EVAc prepared using a monomer in which the group is a methyl group (hereinafter referred to as MPDAc) 1 Each peak in the H-NMR spectrum is assigned as follows: • 0.6~1.0 ppm: Methylene proton (4H) of terminal ethylene units • 1.0~1.85 ppm: Methylene proton (4H) from the intermediate ethylene unit, methylene proton (2H) from the main chain of the structural unit derived from MPDAc, methylene proton (2H) from 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) in the side chain of the structural unit derived from MPDAc • 4.4~5.3 ppm: Methylproton (1H) in vinyl acetate units

[0100] According to the aforementioned 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

[0101] • Degree of saponification of modified EVOH(e) The same applies to denatured EVOH(e) after saponification. 1 ¹H-NMR measurements were performed. The crude dried modified EVOH(e) obtained by synthesis 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 1H-NMR (JEOL Ltd.: "GX-500"). 1 ¹H-NMR measurements revealed 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 modified EVOH(e), the ester groups contained in the structural units derived from MPDAc were also saponified and converted into hydroxyl groups. The result obtained in Synthesis 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 (1.85–2.1 ppm) of vinyl acetate units and methine protons (3.15–4.15 ppm) of vinyl alcohol units.

[0102] • Determination of alkali metal ions 0.5 g of dried denatured EVOH(e) pellets were added to a Teflon pressure vessel manufactured by Actac Corporation, and 5 mL of precision analytical nitric acid manufactured by Wako Pure Chemical Industries, Ltd. was added. After standing for 30 minutes, the vessel was capped with a cap lip with a rupture disc, and the dried denatured EVOH pellets were decomposed by treating them at 150°C for 10 minutes, followed by 180°C for 10 minutes, using Actac Corporation's microwave high-speed decomposition system "Speedwave MWS-2". If the decomposition of the dried denatured EVOH pellets was not completed, the treatment conditions were adjusted as appropriate. The solution was diluted with 10 mL of deionized water, and all of the solution was transferred to a 50 mL volumetric flask and diluted to the final volume with deionized water to obtain the decomposition solution. The above decomposition solution was quantitatively analyzed using an ICP emission spectrometer "Optima 4300 DV" manufactured by PerkinElmer Japan at the following observation wavelengths to quantify the amount of each metal ion. The amount of phosphorus was quantified by quantitative analysis at an observation wavelength of 214.914 nm, and the amount of phosphate compounds was calculated in terms of phosphate root equivalent. The content of boron compounds was obtained in terms of boron element equivalent by quantitative analysis at an observation wavelength of 249.667 nm. Na: 589.592nm K: 766.490nm Mg: 285.213nm Ca: 317.933nm P: 214.914nm B: 249.667nm

[0103] • Quantitative determination of carboxylate ions Dried modified EVOH(e) pellets were pulverized by freeze-milling. The resulting pulverized modified EVOH(e) was sieved using a 1 mm nominal sieve (compliant with standard sieve specifications JIS-Z8801). 10 g of the modified EVOH(e) powder that passed through the sieve and 50 mL of deionized water were placed in a 100 mL Erlenmeyer flask with a stopper, a cooling condenser was attached, and the mixture was stirred and extracted at 95°C for 10 hours. 2 mL of the resulting extract was diluted with 8 mL of deionized water. The diluted extract was quantitatively analyzed using a Yokogawa Electric IC7000 ion chromatograph to determine the amount of carboxylate ions, thereby calculating the amounts of carboxylic acid and carboxylate ions. A calibration curve prepared using an aqueous acetic acid solution was used for the quantification. Ion chromatography measurement conditions: Column: Dionex IonPac "ICE-AS-1" Eluent: 1.0 mmol / L octanesulfonic acid solution Measurement temperature: 35℃ Eluent flow rate: 1mL / min. Sample injection volume: 50 μL

[0104] • Gas barrier properties The gas barrier properties were evaluated based on oxygen permeability. A portion was cut from the multilayer structure and measured using a MOCON INC. OX-TRAN2 / 20 oxygen permeability analyzer (detection limit 0.01 cc / m³). 2 The oxygen permeability was measured using a 1 / day / atm (day·atm) under conditions of 20°C and 65%RH in accordance with the method described in JIS K7126 (isobaric method), and the obtained value was defined as OTR1. OTR1 was evaluated according to the following criteria. A package containing a 360-degree folded portion was prepared using the aforementioned multilayer structure, a portion was cut out so that the folded portion was at the center, and the oxygen permeability was measured, and the obtained value was defined as OTR2. OTR2 was similarly evaluated according to the following criteria. <Judgment criteria> A: 1.0 cc / m 2 ·day · atm or less B: 1.0 cc / m 2 Larger than day / atm, at 5.0cc / m 2 ·day · atm or less C: 5.0 cc / m2 Larger than day / atm, at 10.0cc / m 2 ·day · atm or less D: 10.0 cc / m 2 • Larger than day / atm, 20cc / m 2 ·day · atm or less E: 20cc / m 2 • day • ATM

[0105] • Gas barrier properties OTR2 / OTR1 before and after the bend The ratio of gas barrier OTR1 without a bend to gas barrier OTR2 with a bend (OTR2 / OTR1) was evaluated according to the following criteria. A: OTR2 / OTR1 is between 1.0 and 1.5 B:OTR2 / OTR1 is between 1.5 and 3.0 C:OTR2 / OTR1 is between 3.0 and 5.0 D:OTR2 / OTR1 is between 5.0 and 10.0 E:OTR2 / OTR1 is 10.0 or higher

[0106] • Heat seal strength The heat seal strength of the multilayer structures obtained in each example and comparative example was measured in accordance with JIS Z 0238. Using the multilayer structures, strip-shaped sections with a width of 15 mm were prepared and stacked so that the same layers (sealant layers or modified EVOH(A) layers) were in contact with each other. A 100 mm overlapping section was then tested using a thermal gradient tester manufactured by Toyo Seiki Seisakusho Co., Ltd. at 160°C or 180°C and a pressure of 2.0 kgf / cm². 2 The sample was heat-sealed for 1 second. Using this sample, the T-type peel strength (unit: gf / 15mm) was measured at a tensile speed of 300 mm / min using a Shimadzu Autograph "AGS-H" under an atmosphere of 23°C and 50% RH. Ten measurements were taken, and the average value was calculated. Of the values ​​obtained by heat-sealing at 160°C and 180°C, the higher value was taken as the heat-seal strength and evaluated based on the following evaluation criteria. A:1500gf / 15mm or more B: Less than 1500gf / 15mm, 800gf / 15mm or more C: Less than 800gf / 15mm, 500gf / 15mm or more D: 500gf / less than 15mm, 300gf / 15mm or more E: 300gf / less than 15mm

[0107] • Appearance characteristics and taste of packaged cashew nuts in storage tests. The multilayer structures obtained in the examples and comparative examples were cut to 17 cm x 32 cm, folded horizontally at 8.5 cm and 23.5 cm, overlapped so that the same layers were touching at 1 cm intervals, and heat-sealed at 1 cm intervals to create a package. 50 g of cashew nuts (water activity 0.33) were placed inside, and the package was heat-sealed and sealed. The package was stored for 100 days under conditions of 23°C and 50% RH, and the appearance of the package was judged visually as follows. The criteria for judging appearance characteristics were A, B, C, D, and E, in which order the oil stains became easier to see with the naked eye. In addition, the cashew nuts were tasted by five panelists and judged by consensus according to the following criteria. The criteria for judging taste were A, B, C, D, and E, in which order the change in taste became greater.

[0108] Criteria for determining external characteristics A: No change B: Slight oil stain C: Slight oil stain D: Slight oil stain E: The oil stain is clear.

[0109] • Criteria for judging taste A: It was almost unchanged from before storage. B: The taste has changed slightly compared to before storage. C: The taste has changed slightly compared to before storage. D: The taste has changed slightly compared to before storage. E: The taste has changed compared to before storage.

[0110] The materials used in the examples and comparative examples are as follows: <Paper layer (A)> • Bleached kraft paper: Snow Queen G40, basis weight 50g / m² 2 Manufactured by Daio Paper Corporation • Glassine paper: Thick glassine, basis weight 31g / m² 2 Manufactured by Nippon Paper Industries Co., Ltd. • Bleached kraft paper: Basis weight 140g / m² 2 Manufactured by Nippon Paper Industries Co., Ltd. • Craft ball: S Craft ball, basis weight 290g / m² 2 Manufactured by Nippon Paper Industries Co., Ltd. • Craft ball: S Craft ball, basis weight 450g / m² 2 Manufactured by Nippon Paper Industries Co., Ltd. <Middle layer (F)> • Anchor coating agent: "Zyxen AC" (manufactured by Sumitomo Seika Co., Ltd., polyolefin copolymer) • Bondine TX8030 adhesive resin (manufactured by Arkema) <Sealant layer (G)> • "Zyxen AC" (manufactured by Sumitomo Seika Co., Ltd., a polyolefin copolymer) • Unoriented polypropylene film (CPP, 30μm thickness) "Trefan RNO 3951" (manufactured by Toray Film Processing Co., Ltd.)

[0111] • Example of manufacturing modified EVOH(e) pellets <evoh-1> (1) Synthesis of Modified EVAc A 250L pressurized reactor equipped with a jacket, agitator, nitrogen inlet, ethylene inlet and initiator addition port is used to add vinyl acetate (formula (V), R 5 100 kg of methyl group (hereinafter referred to as VAc), 10 kg of methanol (hereinafter sometimes referred to as MeOH), and 2.9 kg of MPDAc were charged, and after raising the temperature to 60°C, nitrogen was bubbled into the reaction vessel for 30 minutes to purge the inside with nitrogen. Next, ethylene was introduced so that the reaction vessel pressure (ethylene pressure) was 4.9 MPa. After adjusting the temperature inside the reaction vessel to 60°C, 60 g of 2,2'-azobis(2,4-dimethylvaleronitrile) (manufactured by Wako Pure Chemical Industries, Ltd., "V-65") was added as a methanol solution as an initiator, and polymerization was started. During polymerization, the ethylene pressure was maintained at 4.9 MPa and the polymerization temperature at 60°C. After 6 hours, when the polymerization rate of VAc reached 45%, the polymerization was stopped by cooling. The reaction vessel was opened to remove ethylene, and then nitrogen gas was bubbled into it to completely remove ethylene. Next, after removing unreacted VAc under reduced pressure, MeOH was added to EVAc, into which structural units derived from MPDAc had been copolymerized, to obtain a 20% by mass MeOH solution.

[0112] (2) Saponification of modified EVAc A 20% by mass MeOH solution of the modified EVAc obtained in (1) was charged into a 500L reaction vessel equipped with a jacket, stirrer, nitrogen inlet, reflux condenser, and solution addition port. The temperature of this solution was raised to 60°C while blowing nitrogen into it, and 0.5 equivalents of sodium hydroxide 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 distilling off methyl acetate and MeOH. 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 out of the reaction vessel to precipitate modified EVOH(e). The precipitated modified EVOH(e) was collected and pulverized in a mixer. The obtained modified EVOH(e) powder was added to a 1 g / L aqueous acetic acid solution (bath ratio 20: 20 L of aqueous solution per 1 kg of powder) and stirred and washed for 2 hours. The material was dehydrated and then placed in a 1 g / L aqueous acetic acid solution (bath ratio 20) and stirred and washed for 2 hours. The dehydrated material was then placed in deionized water (bath ratio 20) and stirred and washed for 2 hours, repeating this process six times. The conductivity of the washing solution after the sixth wash was measured using a Toa Denpa Kogyo "CM-30ET" and found to be 3 μS / cm. The resulting water content of the hydrated EVOH pellets was 110% by mass. (The water content of hydrated EVOH is calculated as mass% based on dry EVOH. When the mass of the hydrated pellets is Mw and the mass of the dried EVOH is Ms, the water content is calculated as (Mw-Ms) / Ms × 100.)

[0113] 10.5 kg of the hydrated EVOH pellets obtained above were added to 94.5 L of an aqueous solution prepared by dissolving 0.8 g / L of acetic acid, 0.64 g / L of sodium acetate, and 0.016 g / L of phosphoric acid in water, and immersed at 25°C for 6 hours with occasional stirring. After immersion, the hydrated EVOH pellets were dehydrated by centrifugal dewatering, and then dried in a hot air dryer at 80°C for 3 hours, followed by drying at 120°C for 24 hours to obtain pellets of dried EVOH resin composition (EVOH-1). The ethylene unit content (a) of the modified EVAc obtained by the above method was 38.0 mol%, the vinyl acetate unit content (b) was 60.5 mol%, and the structural unit content (c) derived from MPDAc was 1.5 mol%. The values ​​of a, b, and c in modified EVAc are the same as the values ​​of a, b, and c in modified EVOH (e) after saponification treatment. The degree of saponification of the modified EVOH(e) in Synthesis Example 1 was 99.9 moles or higher. The amount of sodium as an alkali metal was 200 ppm (8.7 μmol / g).

[0114] <EVOH-2~10> Modified EVAc and modified EVOH(e) were prepared and analyzed in the same manner as the modified EVOH-1 modified EVOH(e) preparation example, except that the polymerization conditions and the concentration of the solution into which the hydrated modified EVOH pellets were immersed were changed as shown in Table 1. The results are shown in Table 1.

[0115] [Table 1]

[0116] [Example 1] Bleached kraft paper (basis weight 50g / m²) 2 The paper was cut to A4 size, and Zychsen AC was applied to one side using a bar coater No. 12 manufactured by Daiichi Rikagaku Co., Ltd., and dried in a dryer at 120°C for 5 minutes (paper layer / intermediate layer). Next, a mixed solvent of n-propyl alcohol and water (modified EVOH-6 was added to a solution of 65 wt% n-propyl alcohol and 35 wt% water to a solid content concentration of 15 wt%, stirred at 80°C for 3 hours, and it was confirmed that the modified EVOH-6 was completely dissolved) was applied to the side of the bleached kraft paper coated with Zychsen using a bar coater No. 10 manufactured by Daiichi Rikagaku Co., Ltd., and dried in a dryer at 120°C for 5 minutes (paper layer / intermediate layer / modified EVOH layer). A two-component adhesive ("Takelac (trademark) A-385" / "Takenate A-10") was applied to an unoriented polypropylene film (CPP, thickness 30 μm) with a solid content of 2.5 g / m². 2 After coating with the specified basis weight, the bleached kraft paper (paper layer / intermediate layer / modified EVOH layer) was laminated to the modified EVOH layer side by dry lamination to obtain a multilayer structure consisting of a paper layer / intermediate layer / modified EVOH layer / sealant layer. A cross-section was prepared using a microtome, and the thickness of each layer was measured at five points using a microscope, with the average being taken as the thickness of each layer. When the gas barrier properties were measured before bending, it was found to be 0.32 cc / m 2 It received an A rating at day·atm. When the OTR after bending was measured, it was 0.35 cc / m 2 The day-atm value was 1.1, resulting in an A rating. The heat seal strength was 2800gf / 15mm, also resulting in an A rating. After the storage test of the cashew nuts, the appearance of the packaging was evaluated and showed no change, resulting in an A rating. After storage, a taste test of the cashew nuts was conducted and showed almost no change from before storage, resulting in an A rating.

[0117] [Examples 2-17, Comparative Example 1] A multilayer structure was obtained in the same manner as in Example 1, except that the type and thickness of the modified EVOH(e) used in Example 1, the intermediate layer, and the heat-seal layer were changed as shown in Table 2. The thickness of the modified EVOH(e) and the intermediate layer were adjusted by changing the depth (gauge) of the bar coater. The gas barrier properties, gas barrier properties before and after the fold, heat-seal strength, and the appearance characteristics and taste of the package in the cashew nut storage test were evaluated for the obtained multilayer structure in the same manner as in Example 1 and are also shown in Table 2.

[0118] [Example 18] Instead of applying Zychsen and modified EVOH-6 to the kraft paper as in Example 1, the kraft paper was extruded and laminated with the adhesive resin "Bondine TX8030" and modified EVOH-1 using a multilayer extruder. ·Multilayer film forming conditions Extruder: For EVOH: 20mmφ extruder, laboratory type ME CO-EXT (manufactured by Toyo Seiki Co., Ltd.) Ad for use: 20mm diameter extruder SZW20GT-20MG-STD (manufactured by Technovel Co., Ltd.) Modified EVOH(e) extrusion temperature: Feed unit / Compression unit / Metering unit / Die = 175 / 210 / 230 / 230℃ Extrusion temperature: Feed unit / Compression unit / Measuring unit / Die = 100 / 160 / 220 / 220℃ Die for 300mm wide coat hanger (manufactured by Plastics Engineering Laboratory Co., Ltd.) Subsequently, similar to Example 1, a 20 μm two-component adhesive ("Takelac (trademark) A-385" / "Takenate A-10") was applied to an unoriented polypropylene film (CPP) at a solid content of 2.5 g / m². 2 After coating with the specified basis weight, the previously prepared paper / intermediate layer / modified EVOH layer was laminated to the modified EVOH layer side using a dry lamination method to obtain a paper / intermediate layer / modified EVOH layer / / sealant layer. The evaluation results are shown in Table 2.

[0119] [Table 2]

[0120] As shown in the above examples, the present invention provides a multilayer structure that has good gas barrier properties despite being a paper substrate, maintains good gas barrier properties after bending, and has heat seal strength as a packaging body. [Explanation of Symbols]

[0121] 10 vertically formed, filled, and sealed bags 11 multilayer structure 11a end 11b body part

Claims

1. A multilayer structure comprising a paper layer (A) and a modified ethylene vinyl alcohol layer (E) containing a modified ethylene-vinyl alcohol copolymer (e), A multilayer structure in which the modified ethylene-vinyl alcohol copolymer (e) contains structural units (Ia), (Ib), and (Ic) represented by the following formulae, the contents (mol %) a, b, and c of the structural units (Ia), (Ib), and (Ic) satisfy the following formulae (1) to (3), and the degree of saponification (DS) of the modified ethylene-vinyl alcohol copolymer (e) represented by the following formula (4) is 90 mol % or more. 21≦a≦55 (1) 0.1≦c≦10 (2) [100-(a+c)]×0.9≦b≦[100-(a+c)] (3) DS = [(total number of moles of X, Y, and Z that are hydrogen atoms) / (total number of moles of X, Y, and Z)] × 100 (4) [In the formula, a, b, and c represent the content (mol %) of each structural unit relative to 100 mol % of the total of all structural units, and W represents a methyl group or R ２ -OY, where X, Y, and Z each independently represent a hydrogen atom, a formyl group, or an alkanoyl group having 2 to 10 carbon atoms; R １ represents a single bond, an alkylene group having 1 to 9 carbon atoms, or an alkyleneoxy group having 1 to 9 carbon atoms. The alkylene group and the alkyleneoxy group may contain a hydroxyl group, an alkoxy group, or a halogen atom. R ２ represents an alkylene group having 1 to 9 carbon atoms or an alkyleneoxy group having 1 to 9 carbon atoms, and the alkylene group and the alkyleneoxy group may contain a hydroxyl group, an alkoxy group, or a halogen atom. * represents a bonding site.] 【Chemistry 1】

2. The paper layer (A) has a basis weight of 15 to 800 g / m ２ 2. The multilayer structure of claim 1, wherein:

3. 2. The multilayer structure according to claim 1, wherein the modified ethylene-vinyl alcohol copolymer (e) contains alkali metal ions in an amount of 2.5 to 22 μmol / g.

4. The oxygen permeability measured in accordance with JIS-K7126-2 (2006) Part 2 (constant pressure method) under conditions of 20°C and 65% RH is 20 cc / (m ２ 2. The multilayer structure of claim 1, wherein the viscosity is less than or equal to 1000 kJ / day.

5. 2. The multilayer structure according to claim 1, which has a heat seal strength of 300 gf / 15 mm or more as measured over a 15 mm width in accordance with JIS Z 0238.

6. The multilayer structure of claim 1 further comprising an intermediate layer (F) and a sealant layer (G).

7. The multilayer structure according to claim 6 , wherein the intermediate layer (F) comprises a thermosetting resin or a thermoplastic resin (f).

8. 8. The multilayer structure of claim 7, wherein the sealant layer (G) comprises a thermoplastic resin (g).

9. 9. The multilayer structure according to claim 8, wherein the thermoplastic resin (f) and the thermoplastic resin (g) comprise at least one selected from the group consisting of polyethylene, polypropylene, modified polyethylene, and modified polypropylene.

10. The multilayer structure according to claim 1 , wherein the weight M1 of the paper layer (A) and the total weight M2 of the other layers satisfy the following formula (5): 1≦M1 / M2≦300 (5)

11. A package using the multilayer structure according to any one of claims 1 to 10, the package having one or more folded portions.

12. 12. The package according to claim 11, wherein the contents of the package are food products, and the water activity of the food products is between 0.10 and 0.94.

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