Multilayer structures and liquid paper containers

Abstract

To provide multilayer structures, etc., that allow for the formation of paper containers with high gas barrier properties and sufficient strength even in low-temperature environments, while suppressing the occurrence of defects during recycling. [Solution] A multilayer structure comprising a paper layer (A), an inorganic vapor-deposited layer (B), a barrier resin layer (C), an adhesive resin layer (D), and a moisture-proof resin layer (E), wherein the inorganic vapor-deposited layer (B), barrier resin layer (C), adhesive resin layer (D), and moisture-proof resin layer (E) are all directly laminated in this order, the average thickness of the inorganic vapor-deposited layer (B) is 5 nm to 200 nm, the barrier resin layer (C) mainly contains an ethylene-vinyl alcohol copolymer (c) with an ethylene unit content of 20 mol% to 50 mol% and a degree of saponification of 90 mol% or more, the adhesive resin layer (D) mainly contains an adhesive resin (d), and the moisture-proof resin layer (E) mainly contains polyethylene (e).

Description

Technical Field

[0001] The present invention relates to a multilayer structure and a liquid paper container.

Background Art

[0002] Paper containers are widely used as containers for accommodating beverages such as milk and juice, liquid foods such as soup, liquors such as Japanese sake and shochu, and various other liquids other than foods. As materials used for paper containers, multilayer structures in which a resin layer, a vapor deposition layer, a metal foil, etc. are laminated on a paper layer are widely used from the viewpoints of barrier properties, heat sealability, etc. Patent Document 1 describes a paper container formed of a multilayer structure in which a synthetic resin layer or the like is laminated on one surface of a base material mainly composed of a paper layer, and an intermediate layer, a barrier layer, and a sealant layer made of linear low-density polyethylene resin are laminated in this order on the other surface of the base material. A vapor deposition film obtained by vapor-depositing an inorganic substance on a polyethylene terephthalate resin film is used for the barrier layer of the multilayer structure of Patent Document 1.

Prior Art Documents

Patent Documents

[0006] The present invention has been made based on these circumstances, and its purpose is to provide a multilayer structure that has high gas barrier properties in both the unfolded and folded states, can be formed into a paper container that has sufficient strength even in low-temperature environments, and suppresses the occurrence of defects during recycling, as well as a liquid paper container using such a multilayer structure. [Means for solving the problem]

[0007] The aforementioned objective is, [1] A multilayer structure comprising a paper layer (A), an inorganic vapor-deposited layer (B), a barrier resin layer (C), an adhesive resin layer (D), and a moisture-proof resin layer (E), wherein the inorganic vapor-deposited layer (B), barrier resin layer (C), adhesive resin layer (D), and moisture-proof resin layer (E) are all directly laminated in this order, the average thickness of the inorganic vapor-deposited layer (B) is 5 nm to 200 nm, the barrier resin layer (C) mainly contains an ethylene-vinyl alcohol copolymer (c) with an ethylene unit content of 20 mol% to 50 mol% and a degree of saponification of 90 mol% or more, the adhesive resin layer (D) mainly contains an adhesive resin (d), and the moisture-proof resin layer (E) mainly contains polyethylene (e), and does not have a layer mainly containing a resin with a melting point of 200°C or higher, or a metal layer with an average thickness of 1 μm or more; [2] A multilayer structure of [1] further comprising a thermoplastic resin layer (X) interposed between a paper layer (A) and an inorganic vapor-deposited layer (B) or a moisture-proof resin layer (E); [3] A multilayer structure of [1] or [2] having, in this order, a paper layer (A), an inorganic vapor deposition layer (B), a barrier resin layer (C), an adhesive resin layer (D), and a moisture-proof resin layer (E); [4] A multilayer structure of any of [1] to [3], wherein the adhesive resin (d) is acid-modified polyethylene; [5] A multilayer structure of any of [1] to [4], wherein the inorganic vapor-deposited layer (B) is a metal vapor-deposited layer mainly composed of aluminum or an inorganic oxide vapor-deposited layer mainly composed of alumina or silica; [6] A multilayer structure of any of [1] to [5], wherein the barrier resin layer (C) contains at least one polyvalent metal ion selected from the group consisting of magnesium ions, calcium ions, and zinc ions in an amount of 10 ppm to 200 ppm; [7] A multilayer structure of any of [1] to [6], wherein the ethylene-vinyl alcohol copolymer (c) comprises two or more ethylene-vinyl alcohol copolymers with different ethylene unit content; [8] The density of polyethylene(e) is 0.880 g / cm³. 3 More than 0.940g / cm 3 The following are multilayer structures of any of [1] to [7], wherein polyethylene(e) is linear low-density polyethylene, low-density polyethylene, or a mixture thereof; [9] A multilayer structure of any of [1] to [8], wherein the laminate of a barrier resin layer (C), an adhesive resin layer (D), and a moisture-proof resin layer (E) is a co-extruded film, the average thickness of the co-extruded film is 8 μm or more and 120 μm or less, and an inorganic vapor deposition layer (B) is provided on the barrier resin layer (C) side of the co-extruded film;

[10] A multilayer structure of [9] wherein the average thickness of the barrier resin layer (C) is 0.2 μm or more and less than 30 μm, and the ratio of the average thickness of the barrier resin layer (C) to the average thickness of the co-extruded film is less than 25%;

[11] The co-extruded film is substantially unstretched, and is a multilayer structure of [9] or

[10] ;

[12] A multilayer structure of [9] or

[10] wherein the co-extruded film is stretched at least 3 times and less than 12 times in one axial direction;

[13] A multilayer structure of [9] or

[10] , wherein the co-extruded film is stretched by more than 3 times but less than 12 times in each of the two axial directions;

[14] A multilayer structure of any of [9] to

[13] , further comprising a moisture-proof resin layer (F) mainly composed of polyethylene (f);

[15] The density of polyethylene (f) is 0.880 g / cm³. 3 More than 0.940g / cm 3 The following are multilayer structures of polyethylene (f), wherein polyethylene (f) is linear low-density polyethylene, low-density polyethylene, or a mixture thereof

[14] ;

[16] A multilayer structure of

[14] or

[15] in which a moisture-proof resin layer (F) is directly laminated to the co-extruded film;

[17] A multilayer structure of any of [1] to

[16] that does not have an adhesive layer made of a curing type adhesive;

[18] Paper layer (A) has a basis weight of 200 g / m² 2 More than 400g / m 2 A multilayer structure less than any of the [1] to

[17] ;

[19] A multilayer structure of any of [1] to

[18] in which the mass ratio of the paper layer (A) is 0.60 or more of the total multilayer structure;

[20] A multilayer structure of any of the following types [1] to

[19] , wherein the total average thickness ratio of layers mainly composed of polyethylene resin in the parts other than the paper layer (A) is 0.75 or more;

[21] A multilayer structure of any of [1] to

[20] in which the total average thickness ratio of layers mainly composed of resin having ethylene units in the parts other than the paper layer (A) is 0.95 or more;

[22] A multilayer structure having a paper layer (A) on its surface, one of the structures described in [1] to

[21] ;

[23] The oxygen permeation rate measured under conditions of 20°C and 65%RH by the method described in JIS K 7126-2:2006 was 0.5 cc / (m³). 2 A multilayer structure of any of [1] to

[22] that is less than (day·atm);

[24] The paper layer (A) is folded into quarters so that it faces outward from the moisture-proof resin layer (E), and a 5 kg load is applied from above and left to stand for 1 minute to perform the folding treatment. After that, the oxygen permeation rate under conditions of 20°C and 65% RH, measured by the method described in JIS K 7126-2:2006, is 1.0 cc / (m³). 2A multilayer structure of any of [1] to

[23] that is less than (day·atm);

[25] A liquid paper container formed by molding one of the multilayer structures described in [1] to

[24] ; This is achieved by providing [the necessary services / services]. [Effects of the Invention]

[0008] According to the present invention, it is possible to form a paper container that has high gas barrier properties in both the state before and after folding, has sufficient strength even in low-temperature environments, and has a multilayer structure that suppresses the occurrence of defects during recycling, as well as a liquid paper container using such a multilayer structure. [Modes for carrying out the invention]

[0009] <Multilayer structure> The multilayer structure of the present invention comprises a paper layer (A), an inorganic vapor-deposited layer (B), a barrier resin layer (C), an adhesive resin layer (D), and a moisture-proof resin layer (E). The inorganic vapor-deposited layer (B), barrier resin layer (C), adhesive resin layer (D), and moisture-proof resin layer (E) are all directly laminated in this order. The average thickness of the inorganic vapor-deposited layer (B) is 5 nm to 200 nm. The barrier resin layer (C) mainly contains an ethylene-vinyl alcohol copolymer (c) with an ethylene unit content of 20 mol% to 50 mol% and a degree of saponification of 90 mol% or more. The adhesive resin layer (D) mainly contains an adhesive resin (d). The moisture-proof resin layer (E) mainly contains polyethylene (e). The structure does not contain a layer mainly composed of a resin with a melting point of 200°C or higher, nor a metal layer with an average thickness of 1 μm or more. Hereinafter, the ethylene-vinyl alcohol copolymer will also be referred to as "EVOH".

[0010] The multilayer structure of the present invention exhibits high gas barrier properties in both the unfolded and folded states, and enables the formation of paper containers with sufficient strength even in low-temperature environments, thereby suppressing the occurrence of defects during recycling. The reason for this is not entirely clear, but the following reasons are speculated. The multilayer structure has a structure in which an inorganic vapor-deposited layer (B) having a predetermined thickness and a barrier resin layer (C) mainly composed of EVOH, which has excellent gas barrier properties, are directly laminated, resulting in high gas barrier properties in both the unfolded and folded states. Furthermore, the moisture-proof resin layer (E) of the multilayer structure is mainly composed of polyethylene (e). Therefore, by heat-sealing this moisture-proof resin layer (E) to form the paper container, it is possible to form a paper container with sufficient strength even in low-temperature environments. Furthermore, the multilayer structure has a relatively thin inorganic vapor-deposited layer (B), the barrier resin layer (C) and moisture-proof resin layer (E) are mainly composed of a predetermined resin, and it does not contain layers mainly composed of resins with a melting point of 200°C or higher, nor does it have metal layers with an average thickness of 1 μm or more, thus suppressing the occurrence of defects during recycling.

[0011] In this specification, "main component" refers to the component that is present in the largest quantity by mass. The "average thickness" of each layer refers to the average value of the thickness measured at any five locations. "ppm" refers to the content by mass (mass ppm). "Polyethylene" refers to a homopolymer of ethylene, a copolymer of 80 mol% or more of ethylene and 20 mol% or less of α-olefin monomer, and a copolymer of 90 mol% or more of ethylene and less than 10 mol% of a non-olefin monomer whose functional groups do not contain atoms other than carbon, oxygen, and hydrogen atoms. "Acid-modified polyethylene" refers to a polymer obtained by modifying polyethylene with an acid. Acid-modified polyethylene may be a polymer in which at least one of an acidic group and an acid anhydride group is introduced to polyethylene. The term "polyethylene resin" refers to polyethylene and modified polyethylene (such as acid-modified polyethylene). Modified polyethylene refers to a polymer obtained by modifying polyethylene. In addition, the "surface" in the multilayer structure does not mean to distinguish between the front and back, but refers to the exposed surface. That is, there are two surfaces in the multilayer structure. Similarly, there are two outermost layers in the multilayer structure.

[0012] Hereinafter, each layer, layer configuration, etc. of the multilayer structure according to an embodiment of the present invention will be described in detail.

[0013] (Paper layer (A)) The paper layer (A) is usually a layer serving as a base material in the multilayer structure of the present invention. As the paper layer (A), general paper mainly composed of plant-derived pulp can be used. In addition to pulp, the paper layer (A) may contain a sizing agent, a filler, a paper strength enhancer, a yield improver, a pH adjuster, a drainage improver, a water resistance agent, a softener, an antistatic agent, an antifoaming agent, a slime control agent, a dye, a pigment, etc.

[0014] Examples of the paper constituting the paper layer (A) include kraft paper, fine paper, medium paper, alkaline paper, cardboard, glassine paper, semi-glassine paper, parchment paper, etc. Kraft paper or cardboard is preferable, and cardboard is more preferable.

[0015] The basis weight (mass per unit area) of the paper layer (A) is not particularly limited, and for example, it can be 50 g / m 2 or more and 500 g / m 2 or less, but it is preferably 100 g / m 2 or more and 450 g / m 2 or less, more preferably 200 g / m 2 or more and 400 g / m 2 or less, still more preferably 220 g / m 2 or more and 350 g / m 2 or less, and even more preferably 240 g / m 2 or more and 300 g / m 2A value less than the above-mentioned lower limit is even more preferable. If the basis weight of the paper layer (A) is equal to or greater than the above-mentioned lower limit, the strength of the resulting paper container in a low-temperature environment can be further increased. On the other hand, if the basis weight of the paper layer (A) is less than the above-mentioned upper limit, the moldability can be improved.

[0016] For example, the density of the paper layer (A) is 0.5 g / cm³. 3 More than 1.5g / cm 3 The following is preferable: 0.7 g / cm³ 3 More than 1.3g / cm 3 The following are preferable.

[0017] The paper used in the paper layer (A) can be manufactured by known methods. Alternatively, commercially available paper can be used for the paper layer (A).

[0018] (Inorganic vapor deposited layer (B)) The inorganic vapor-deposited layer (B) primarily serves to ensure gas barrier properties in the multilayer structure of the present invention.

[0019] The inorganic vapor-deposited layer (B) can be formed by depositing inorganic material. Typically, the inorganic vapor-deposited layer (B) is formed by depositing inorganic material onto the surface of the barrier resin layer (C). Examples of inorganic materials include metals (e.g., aluminum, copper, etc.), oxides (e.g., alumina, silica, etc.), nitrides (e.g., silicon nitride, etc.), nitride oxides (e.g., silicon oxynitride, etc.), and carbidine nitrides (e.g., silicon carbonitride, etc.).

[0020] As the inorganic vapor-deposited layer (B), a metal vapor-deposited layer or an inorganic oxide vapor-deposited layer is preferred. If light shielding and barrier properties after bending are important, a metal vapor-deposited layer is more preferred as the inorganic vapor-deposited layer (B), a metal vapor-deposited layer mainly composed of aluminum is preferred, and an aluminum vapor-deposited layer may also be used. On the other hand, if preventing discoloration during recycling is important, an inorganic oxide vapor-deposited layer is preferred as the inorganic vapor-deposited layer (B), and an inorganic oxide vapor-deposited layer mainly composed of alumina (aluminum oxide) or silica (silicon oxide) is preferred.

[0021] Furthermore, in metal vapor deposition layers primarily composed of aluminum (inorganic vapor deposition layer (B)), irreversible oxidation occurs, and some aluminum oxide may be present. In metal vapor deposition layers primarily composed of aluminum (inorganic vapor deposition layer (B)), the molar ratio of oxygen atoms to aluminum atoms is (O mol / Al mol The value of ) is preferably 0.5 or less, more preferably 0.3 or less, and even more preferably 0.1 or less.

[0022] The lower limit of the average thickness of the inorganic vapor-deposited layer (B) is 5 nm, preferably 10 nm, more preferably 20 nm, and even more preferably 30 nm. Having an average thickness of the inorganic vapor-deposited layer (B) above the lower limit enhances gas barrier properties, etc. The upper limit of the average thickness of the inorganic vapor-deposited layer (B) is 200 nm, preferably 150 nm, more preferably 120 nm, and even more preferably 80 nm. Having an average thickness of the inorganic vapor-deposited layer (B) below the upper limit suppresses defects, discoloration, etc., during recycling. Recycled products (molten products) with suppressed defects and discoloration are preferable because they have a good appearance, etc.

[0023] The inorganic vapor deposition layer (B) can be formed by known physical or chemical vapor deposition methods. Specifically, these include vacuum vapor deposition, sputtering, ion plating, ion beam mixing, plasma CVD, laser CVD, MO-CVD, and thermal CVD. Physical vapor deposition is preferred, and vacuum vapor deposition is more preferred.

[0024] Before performing vapor deposition, the surface of the layer to be deposited (for example, the barrier resin layer (C)) may be plasma-treated. Known methods can be used for plasma treatment, and atmospheric pressure plasma treatment is preferred. Examples of discharge gases in atmospheric pressure plasma treatment include nitrogen gas, helium, neon, argon, krypton, xenon, and radon. Among these, nitrogen, helium, and argon are preferred, and nitrogen is more preferred from the viewpoint of cost reduction.

[0025] The inorganic vapor-deposited layer (B) may consist of a single layer or multiple layers.

[0026] (Barrier resin layer (C)) The barrier resin layer (C) mainly contains EVOH(c) with an ethylene unit content of 20 mol% to 50 mol% and a degree of saponification of 90 mol% or more. Because the multilayer structure of the present invention is equipped with such a barrier resin layer (C), it can exhibit high gas barrier properties both before and after bending treatment.

[0027] EVOH(c) is a copolymer having ethylene units and vinyl alcohol units. EVOH(c) is usually obtained by saponification of an ethylene-vinyl ester copolymer. EVOH(c) may have residual vinyl ester units. The production and saponification of ethylene-vinyl ester copolymers can be carried out by known methods. Examples of vinyl esters include vinyl acetate, vinyl formate, vinyl propionate, vinyl valerate, vinyl caprate, vinyl laurate, vinyl stearate, vinyl pivalate, vinyl versaticate, and other aliphatic carboxylic acid vinyl esters, with vinyl acetate being preferred.

[0028] The lower limit of the ethylene unit content of EVOH(c) is 20 mol%, preferably 24 mol%, and more preferably 28 mol% or 30 mol%. Having an ethylene unit content of EVOH(c) above the lower limit enhances strength in low-temperature environments and suppresses defects and discoloration during recycling. The upper limit of the ethylene unit content of EVOH(c) is 50 mol%, preferably 46 mol%, and more preferably 42 mol% or 38 mol%. Having an ethylene unit content of EVOH(c) below the upper limit enhances gas barrier properties after bending.

[0029] The lower limit of the degree of saponification of EVOH(c) is 90 mol%, preferably 95 mol%, more preferably 99 mol%, and even more preferably 99.9 mol%. When the degree of saponification of EVOH(c) is above the lower limit, the gas barrier properties tend to be further enhanced. The upper limit of the degree of saponification of EVOH(c) may be 100 mol%.

[0030] EVOH(c) may have structural units other than ethylene units, vinyl alcohol units, and vinyl ester units, to the extent that the objectives of the present invention are not hindered. In particular, by introducing a modified group containing a primary hydroxyl group having a specific structure, it may be possible to achieve a high level of both gas barrier properties and moldability of EVOH(c). The content of other monomer units is preferably 5% by mass or less, more preferably 3% by mass or less, even more preferably 1% by mass or less, and particularly preferably substantially absent. Other 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, ethyl vinyl ether, n-propyl vinyl ether, i-propyl vinyl ether Examples include vinyl ethers such as 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, 1,3-diacetoxy-2-methylenepropane, 1,3-dipropionyloxy-2-methylenepropane, and 1,3-dibutyronyloxy-2-methylenepropane.

[0031] The MFR (at 190°C, with a 2.16 kg load) for EVOH(c) is preferably 0.5 g / 10 min to 12 g / 10 min, more preferably 0.8 g / 10 min to 8.0 g / min, and even more preferably 1.2 g / 10 min to 4.0 g / min.

[0032] EVOH(c) may be used alone or in combination of two or more types.

[0033] EVOH(c) may contain two or more types of EVOH with different ethylene unit content. In such cases, it is possible to achieve a better balance between the gas barrier properties after bending and the strength in low-temperature environments. The two types of EVOH with different ethylene unit content may be two types of EVOH with different melting points. For example, when the melting point is measured by DSC, the peak temperature corresponding to each EVOH may be confirmed. In the measurement of the melting point by DSC, the temperature is raised from 30°C to 250°C at a rate of 10°C / min, cooled at 50°C / min, and the melting point is determined from the peak temperature measured by secondary heating.

[0034] Of the two types of EVOH(c), the ethylene unit content of EVOH(c1), which has a low ethylene unit content, is preferably 20 mol% to 40 mol%, and more preferably 24 mol% to 32 mol%. Of the two types of EVOH(c), the ethylene unit content of EVOH(c2), which has a high ethylene unit content, is preferably 32 mol% to 50 mol%, and more preferably 38 mol% to 48 mol%.

[0035] The difference in ethylene unit content between EVOH(c2) and EVOH(c1) (c2-c1), that is, the value obtained by subtracting the ethylene unit content of EVOH(c1) from the ethylene unit content of EVOH(c2), is preferably 4 mol% or more and 40 mol% or less, more preferably 8 mol% or more and 30 mol% or less, even more preferably 12 mol% or more and 25 mol% or less, and even more preferably 15 mol% or more and 20 mol% or less.

[0036] The mass ratio (c1 / c2) of EVOH(c1) to EVOH(c2), that is, the mass ratio of the EVOH(c1) content to the EVOH(c2) content, is preferably 50 / 50 or more and 95 / 5 or less, more preferably 60 / 40 or more and 90 / 10 or less, and even more preferably 70 / 30 or more and 85 / 15 or less.

[0037] The lower limit of the EVOH(c) content in the barrier resin layer (C) is preferably 70% by mass, more preferably 80% by mass, even more preferably 90% by mass, and may also be 95% by mass, 99% by mass, or 99.9% by mass, from the viewpoint of gas barrier properties, etc. The upper limit of the EVOH(c) content in the barrier resin layer (C) may be 100% by mass or 99.99% by mass.

[0038] The barrier resin layer (C) preferably contains at least one polyvalent metal ion selected from the group consisting of magnesium ions, calcium ions, and zinc ions. The lower limit of the polyvalent metal ion content in the barrier resin layer (C) is preferably 10 ppm, more preferably 30 ppm, even more preferably 50 ppm, and in cases where suppressing defects in the recycled resin is of particular importance, 80 ppm may be even more preferable. By containing the polyvalent metal ions in the barrier resin layer (C) at or above the lower limit, the occurrence of defects during recycling is further suppressed. On the other hand, the upper limit of the polyvalent metal ion content in the barrier resin layer (C) may be, for example, 300 ppm, but is preferably 200 ppm, more preferably 150 ppm, even more preferably 120 ppm, and in cases where suppressing discoloration of the recycled resin is of particular importance, 80 ppm may be even more preferable. By keeping the polyvalent metal ion content in the barrier resin layer (C) below the upper limit, the occurrence of discoloration during recycling is suppressed.

[0039] The aforementioned polyvalent metal ions preferably include magnesium ions, and more preferably magnesium ions. In this case, the occurrence of defects during recycling is further suppressed.

[0040] The polyvalent metal ion is preferably present in the barrier resin layer (C) as a cation constituting the salt, and more preferably present in the barrier resin layer (C) as a cation constituting the carboxylate salt. In salts such as carboxylate salts, the polyvalent metal ion and the anion may be bonded or free.

[0041] The carboxylate salt containing the polyvalent metal ion is preferably a higher fatty acid salt. Specifically, it is preferably a salt of a carboxylic acid having 12 or more carbon atoms. When the polyvalent metal ion exists in the form of such a higher fatty acid salt, the occurrence of discoloration during recycling is further suppressed. Examples of carboxylic acids having 12 or more carbon atoms include lauric acid, lauric acid, tridecyl acid, myristic acid, pentadecyl acid, palmitic acid, heptadecyl acid, stearic acid, basic stearic acid, hydroxystearic acid, basic hydroxystearic acid, nonadecanoic acid, oleic acid, behenic acid, montanic acid, and linoleic acid. The number of carbon atoms in the carboxylic acid may be 12 to 30, 14 to 26, or 16 to 22.

[0042] The polyvalent metal ions may be present in the barrier resin layer (C) as cations constituting fatty acid salts (acetates, propions, etc.) with 11 or fewer carbon atoms, or salts other than fatty acid salts (nitrates, sulfates, etc.). Some or all of the polyvalent metal ions may be present in a state coordinated to, for example, the hydroxyl group of EVOH(c).

[0043] The barrier resin layer (C) may contain, as optional components other than EVOH(c) and the polyvalent metal ions or salts containing the polyvalent metal ions, boron compounds, carboxylic acids, phosphorus compounds, metal ions other than the polyvalent metal ions, antioxidants, ultraviolet absorbers, plasticizers, antistatic agents, lubricants, colorants, fillers, heat stabilizers, and other resins other than EVOH(c). The barrier resin layer (C) may contain two or more of these optional components.

[0044] Examples of boron compounds include boric acids such as orthoboric acid, metaboric acid, and tetraboric acid; boric acid esters such as triethyl borate and trimethyl borate; alkali metal salts or alkaline earth metal salts of the boric acids, borates such as borax; and boron hydrides. The content of the boron compound in the barrier resin layer (C) is preferably 10 ppm to 1,000 ppm, and more preferably 50 ppm to 400 ppm. By setting the content of the boron compound within the above range, melt moldability, appearance, etc., are improved. The content of the boron compound is expressed in terms of elemental boron content.

[0045] Examples of carboxylic acids include formic acid, acetic acid, propionic acid, butyric acid, lactic acid, and their salts. Preferred carboxylic acids are those having four or fewer carbon atoms or saturated carboxylic acids, with acetic acid being more preferred. Furthermore, the carboxylic acids may also include carboxylic acid salts containing the aforementioned polyvalent metal ions.

[0046] Examples of phosphorus compounds include phosphates such as phosphoric acid and phosphorous acid. The phosphate may be in the form of monophosphate, dicate, or tertiary phosphate. The cation species of the phosphate is not particularly limited, but alkali metal salts or alkaline earth metal salts are preferred, and among these, sodium dihydrogen phosphate, potassium dihydrogen phosphate, disodium hydrogen phosphate, or dipotassium hydrogen phosphate are more preferred. The phosphorus compound content in the barrier resin layer (C) is preferably 1 ppm to 200 ppm, and more preferably 10 ppm to 100 ppm. By keeping the phosphorus compound content within the above range, thermal stability is improved and defects and discoloration during recycling are suppressed. The phosphorus compound content is expressed in terms of phosphate equivalent.

[0047] Examples of metal ions other than the aforementioned polyvalent metal ions include monovalent metal ions and polyvalent metal ions other than the aforementioned polyvalent metal ions, with monovalent metal ions being preferred. Among monovalent metal ions, alkali metal ions are preferred.

[0048] Examples of alkali metal ions include lithium ions, sodium ions, and potassium ions, with sodium ions or potassium ions being preferred from the viewpoint of industrial availability. Examples of alkali metal salts containing alkali metal ions include aliphatic carboxylates, aromatic carboxylates, carbonates, hydrochlorides, nitrates, sulfates, phosphates, and metal complexes. Among these, aliphatic carboxylates or phosphates are preferred from the viewpoint of availability, and specifically, sodium acetate, potassium acetate, sodium phosphate, or potassium phosphate are preferred. The alkali metal ion content in the barrier resin layer (C) is preferably 10 ppm to 1,000 ppm, and more preferably 100 ppm to 400 ppm. By keeping the alkali metal ion content within the above range, interlayer adhesion is improved, and discoloration during recycling is suppressed.

[0049] Examples of antioxidants include 2,5-di-t-butylhydroquinone, 2,6-di-t-butyl-p-cresol, 4,4'-thiobis(6-t-butylphenol), 2,2'-methylene-bis(4-methyl-6-t-butylphenol), and octadecyl-3-(3',5'-di-t-butyl-4'-hydroxyphenyl)propionate.

[0050] Examples of UV absorbers include ethylene-2-cyano-3,3'-diphenyl acrylate, 2-(2'-hydroxy-5'-methylphenyl)benzotriazole, 2-(2'-hydroxy-3'-t-butyl-5'-methylphenyl)-5-chlorobenzotriazole, 2-hydroxy-4-methoxybenzophenone, 2,2'-dihydroxy-4-methoxybenzophenone, and 2-hydroxy-4-oxybenzophenone.

[0051] Examples of plasticizers include dimethyl phthalate, diethyl phthalate, dioctyl phthalate, wax, liquid paraffin, and phosphate esters.

[0052] Examples of antistatic agents include pentaerythritol monostearate, sorbitan monopalmitate, sulfated polyolefins, polyethylene oxide, and polyethylene glycol (trade name: Carbowax).

[0053] Examples of lubricants include ethylenebisstearamide and butyl stearate.

[0054] Examples of colorants include carbon black, phthalocyanine, quinacridone, indoline, azo pigments, and red iron oxide.

[0055] Examples of fillers include glass fiber, wollastonite, calcium silicate, talc, and montmorillonite.

[0056] Examples of heat stabilizers include hindered phenol compounds and hindered amine compounds.

[0057] Other resins besides EVOH(c) include, for example, polyamides and polyolefins.

[0058] The barrier resin layer (C) may be an unstretched layer or a stretched layer. When the barrier resin layer (C) is a stretched layer, good gas barrier properties can be exhibited even when the barrier resin layer (C) is relatively thin.

[0059] The lower limit of the average thickness of the barrier resin layer (C) is preferably 0.1 μm, more preferably 0.2 μm, even more preferably 0.4 μm, and even more preferably 0.5 μm, 0.6 μm, 0.8 μm, or 1 μm, and may also be 2 μm. Having an average thickness of the barrier resin layer (C) above the lower limit enhances gas barrier properties, etc. The upper limit of the average thickness of the barrier resin layer (C) is preferably 30 μm, more preferably 20 μm, even more preferably 15 μm, even more preferably 10 μm or 5 μm, and may also be 3 μm. Having an average thickness of the barrier resin layer (C) below the upper limit suppresses discoloration during recycling, etc.

[0060] The barrier resin layer (C) may consist of a single layer or multiple layers.

[0061] (Adhesive resin layer (D)) The adhesive resin layer (D) mainly contains adhesive resin (d). The adhesive resin layer (D) adheres the barrier resin layer (C) and the moisture-proof resin layer (E).

[0062] The adhesive resin (d) is not particularly limited as long as it is an adhesive resin, and examples include acid-modified polyolefins (carboxylic acid-modified polyolefins, sulfonic acid-modified polyolefins, etc.) and epoxy-modified polyolefins. The adhesive resin (d) is preferably a thermoplastic resin. The adhesive resin (d) is preferably an acid-modified polyolefin (acid-modified polyethylene, acid-modified polypropylene, etc.), and more preferably acid-modified polyethylene. Furthermore, the adhesive resin (d) is also preferably a carboxylic acid-modified polyolefin, and more preferably carboxylic acid-modified polyethylene.

[0063] Carboxylic acid-modified polyolefins may be polyolefins having a carboxyl group or its anhydride group. Carboxylic acid-modified polyolefins (polyolefins having a carboxyl group or its anhydride group) can be obtained, for example, by chemically bonding an ethylenically unsaturated carboxylic acid or its anhydride to an unmodified polyolefin through an addition reaction, graft reaction, or the like.

[0064] Polyethylene is preferred as the unmodified polyolefin used in the production of carboxylic acid-modified polyolefins.

[0065] Examples of ethylenically unsaturated carboxylic acids and their anhydrides include monocarboxylic acids, monocarboxylic acid esters, dicarboxylic acids, dicarboxylic acid monoesters, dicarboxylic acid diesters, and dicarboxylic acid anhydrides. Specifically, 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. Of these, dicarboxylic acid anhydrides such as maleic anhydride and itaconic anhydride are preferred, and maleic anhydride is more preferred. That is, the adhesive resin (d) is preferably a maleic anhydride-modified polyolefin, and more preferably a maleic anhydride-modified polyethylene.

[0066] Carboxylic acid-modified polyolefins are obtained by introducing an ethylenically unsaturated carboxylic acid or its anhydride into an unmodified polyolefin by an addition reaction or graft reaction in the presence of a solvent such as xylene and a catalyst such as a peroxide. The lower limit of the amount of carboxylic acid or its anhydride added or grafted (degree of modification) to the unmodified polyolefin is preferably 0.01% by mass, and more preferably 0.02% by mass, relative to the unmodified polyolefin. On the other hand, the upper limit of the amount added or grafted (degree of modification) is preferably 15% by mass, and more preferably 10% by mass, relative to the unmodified polyolefin.

[0067] For acid-modified polyolefins such as carboxylic acid-modified polyolefins, the acid value is preferably 0.3 mg KOH / g or more and 5.0 mg KOH / g or less, and more preferably 1.0 mg KOH / g or more and 3.0 mg KOH / g or less.

[0068] The MFR (190°C, 2.16 kg load) of the adhesive resin (d) is preferably 0.5 g / 10 min to 12 g / 10 min, and more preferably 1.0 g / 10 min to 8.0 g / min.

[0069] The adhesive resin (d) may be used alone or in combination of two or more types.

[0070] The content of the adhesive resin (d) in the adhesive resin layer (D) is preferably 80% by mass or more and 100% by mass or less, more preferably 90% by mass or more and 100% by mass or less, and even more preferably 97% by mass or more and 100% by mass or less. The adhesive resin layer (D) may also contain components other than the adhesive resin (d), such as antioxidants, ultraviolet absorbers, plasticizers, antistatic agents, lubricants, colorants, fillers, heat stabilizers, and other resins other than the adhesive resin (d).

[0071] The adhesive resin layer (D) may be an unstretched layer or a stretched layer.

[0072] The lower limit of the average thickness of the adhesive resin layer (D) is preferably 0.1 μm, more preferably 0.5 μm, even more preferably 1 μm, and may also be 2 μm. Having an average thickness of the adhesive resin layer (D) above the lower limit ensures sufficient adhesion and further suppresses defects and discoloration during recycling. The upper limit of the average thickness of the adhesive resin layer (D) is preferably 20 μm, more preferably 10 μm, even more preferably 5 μm, and may also be 3 μm. Having an average thickness of the adhesive resin layer (D) below the upper limit further suppresses defects and discoloration during recycling.

[0073] The adhesive resin layer (D) may consist of a single layer or multiple layers.

[0074] (Moisture-proof resin layer (E)) The moisture-proof resin layer (E) mainly contains polyethylene (e). Because the moisture-proof resin layer (E) mainly contains polyethylene (e), the multilayer structure of the present invention can exhibit sufficient moisture resistance. Furthermore, because the moisture-proof resin layer (E) mainly contains polyethylene (e), the multilayer structure of the present invention can form paper containers with sufficient strength even in low-temperature environments, and the occurrence of defects during recycling is suppressed. The moisture-proof resin layer (E) may also be a heat-sealable layer for bonding moisture-proof resin layers (E) to each other, or to other layers by heat sealing. From the viewpoint of further increasing the strength of the resulting paper container in low-temperature environments, the moisture-proof resin layer (E) may be the outermost layer in the multilayer structure.

[0075] The type of polyethylene(e) is not particularly limited, and examples include high-density polyethylene, low-density polyethylene, and linear low-density polyethylene. Among these, linear low-density polyethylene, low-density polyethylene, or mixtures thereof are preferred. Linear low-density polyethylene is a resin obtained by polymerizing ethylene with an α-olefin having 3 or more carbon atoms. Examples of α-olefins having 3 or more carbon atoms include propylene, 1-butene, 1-pentene, 1-hexene, 1-octene, 1-decene, 1-dodecene, and 4-methyl-1-pentene. Among these, linear low-density polyethylene is preferably obtained by polymerizing ethylene with an α-olefin having 6 or more carbon atoms, and more preferably obtained by polymerizing ethylene with an α-olefin having 8 or more carbon atoms. When the number of carbon atoms in the α-olefin copolymerized with ethylene is relatively large, various mechanical strengths such as puncture strength and tensile strength may be particularly improved. Furthermore, it is preferable to use a metallocene catalyst as the polymerization catalyst. Linear low-density polyethylene polymerized using a metallocene catalyst is produced by copolymerizing ethylene and α-olefin in the presence of a catalyst formed from a compound having at least one ligand with a cyclopentadienyl skeleton and a transition metal of Group 4 of the periodic table as the central metal atom (preferably a compound having zirconium as the central metal atom), an organoaluminum oxy compound, and various components added as needed. Linear low-density polyethylene polymerized using a metallocene catalyst has excellent melt-molding properties, and the resulting multilayer film has an excellent balance of heat resistance, flexibility, and mechanical strength. By using such polyethylene, the strength of the molded paper container can be further increased in low-temperature environments. One or more types of polyethylene(e) can be used.

[0076] For example, the upper limit of the density of polyethylene(e) is 0.96 g / cm³. 3 It can be made to be 0.940 g / cm³ 3 Preferably, 0.930 g / cm³ 3This is more preferable. The lower limit of the density of polyethylene(e) is 0.880 g / cm³. 3 Preferably, 0.890 g / cm³ 3 More preferably, 0.900 g / cm³ 3 Or 0.910 g / cm³ 3 This is also acceptable. By using polyethylene (e) with a relatively low density, the strength of the molded paper container in low-temperature environments can be further increased.

[0077] For polyethylene(e), the MFR (at 190°C, 2.16 kg load) is preferably 0.4 g / 10 min to 4.0 g / 10 min, and more preferably 0.8 g / 10 min to 2.0 g / min.

[0078] The polyethylene(e) content in the moisture-proof resin layer (E) is preferably 80% to 100% by mass, more preferably 90% to 100% by mass, and even more preferably 97% to 100% by mass. The moisture-proof resin layer (E) may also contain other components besides polyethylene(e), such as antioxidants, ultraviolet absorbers, plasticizers, antistatic agents, lubricants, colorants, fillers, heat stabilizers, and other resins other than polyethylene(e).

[0079] The moisture-proof resin layer (E) may be an unstretched layer or a stretched layer.

[0080] The lower limit of the average thickness of the moisture-proof resin layer (E) is preferably 1 μm, more preferably 5 μm, even more preferably 10 μm, even more preferably 20 μm, and may also be 30 μm, 40 μm, or 45 μm. Having an average thickness of the moisture-proof resin layer (E) equal to or greater than the aforementioned lower limit allows for sufficient heat sealing, resulting in the formation of paper containers with higher strength in low-temperature environments. Furthermore, having an average thickness of the moisture-proof resin layer (E) equal to or greater than the aforementioned lower limit ensures sufficient moisture resistance. The upper limit of the average thickness of the moisture-proof resin layer (E) is preferably 200 μm, more preferably 100 μm, and may also be 50 μm.

[0081] The moisture-proof resin layer (E) may consist of a single layer or multiple layers.

[0082] (Thermoplastic resin layer (X)) The multilayer structure of the present invention preferably further comprises a thermoplastic resin layer (X) interposed between the paper layer (A) and the inorganic vapor-deposited layer (B) or moisture-proof resin layer (E). In other words, the multilayer structure of the present invention preferably has a layer configuration in which the paper layer (A) and the inorganic vapor-deposited layer (B) or moisture-proof resin layer (E) are laminated via a thermoplastic resin layer (X). It may also be said that the paper layer (A) is laminated via a thermoplastic resin layer (X) on one surface of a laminate (composite film) of the inorganic vapor-deposited layer (B), barrier resin layer (C), adhesive resin layer (D), and moisture-proof resin layer (E). By having such a thermoplastic resin layer (X) in the multilayer structure, it is possible to improve the adhesion between the paper layer (A) and the inorganic vapor-deposited layer (B) or moisture-proof resin layer (E). Furthermore, because the paper layer (A) and the inorganic vapor-deposited layer (B) or moisture-proof resin layer (E) are bonded together by a thermoplastic resin layer (X), defects and discoloration during recycling can be further suppressed.

[0083] The thermoplastic resin layer (X) is mainly composed of a thermoplastic resin. The thermoplastic resin is not particularly limited as long as it is a thermoplastic resin with a melting point of less than 200°C, and examples include polyolefins, polystyrenes, polycarbonates, acrylic resins, and the aforementioned adhesive resins (such as acid-modified polyolefins). Among these, polyolefins or acid-modified polyolefins are preferred, polyolefins are more preferred, and polyethylene is even more preferred. By making the thermoplastic resin layer (X) mainly composed of such a thermoplastic resin, it is possible to suppress the occurrence of discoloration during recycling.

[0084] The thermoplastic resin content in the thermoplastic resin layer (X) is preferably 80% to 100% by mass, more preferably 90% to 100% by mass, and even more preferably 97% to 100% by mass. The thermoplastic resin layer (X) may also contain components other than the thermoplastic resin, such as antioxidants, ultraviolet absorbers, plasticizers, antistatic agents, lubricants, colorants, fillers, heat stabilizers, and other resins other than the thermoplastic resin.

[0085] The lower limit of the average thickness of the thermoplastic resin layer (X) is preferably 1 μm, more preferably 3 μm, even more preferably 5 μm, and even more preferably 10 μm. Having an average thickness of the thermoplastic resin layer (X) equal to or greater than the lower limit improves the adhesion between the paper layer (A) and the inorganic vapor-deposited layer (B). The upper limit of the average thickness of the thermoplastic resin layer (X) is preferably 100 μm, more preferably 50 μm, and may also be 30 μm.

[0086] The thermoplastic resin layer (X) is preferably an extruded resin layer. That is, the paper layer (A) and the inorganic vapor-deposited layer (B) (or a co-extruded film with the inorganic vapor-deposited layer (B) described later on one side) or the moisture-proof resin layer (E) (or a co-extruded film with the moisture-proof resin layer (E) described later on one side) are preferably laminated by sandwich lamination. However, the paper layer (A) and the inorganic vapor-deposited layer (B) (or a co-extruded film with the inorganic vapor-deposited layer (B) described later on one side) or the moisture-proof resin layer (E) (or a co-extruded film with the moisture-proof resin layer (E) described later on one side) may be laminated by other methods, such as dry lamination. In this case, the layer interposed between the paper layer (A) and the inorganic vapor-deposited layer (B) or the moisture-proof resin layer (E) may be an adhesive layer other than the thermoplastic resin layer (X).

[0087] (Co-extruded film) In the multilayer structure of the present invention, the laminate of the barrier resin layer (C), adhesive resin layer (D), and moisture-proof resin layer (E) is preferably a co-extruded film. That is, the barrier resin layer (C), adhesive resin layer (D), and moisture-proof resin layer (E) are preferably formed by co-extrusion. This allows for a high level of balance between film properties such as barrier properties and flexibility, process passability, and economic efficiency. Furthermore, it is preferable that an inorganic vapor-deposited layer (B) is provided on the barrier resin layer (C) side of the co-extruded film. In this embodiment, the inorganic vapor-deposited layer (B) may be provided by vapor deposition on the barrier resin layer (C) side of the co-extruded film. By using such a co-extruded film, the productivity, gas barrier properties, etc., of the multilayer structure can be improved.

[0088] The lower limit of the average thickness of the co-extruded film is preferably 8 μm, more preferably 15 μm, and even more preferably 25 μm. An average thickness of the co-extruded film above this lower limit enhances gas barrier properties and the strength of the resulting paper container in low-temperature environments. The upper limit of the average thickness of the co-extruded film is preferably 120 μm, more preferably 80 μm, and even more preferably 60 μm. An average thickness of the co-extruded film below this upper limit allows for the thinning of multilayer structures. The average thickness of the co-extruded film is equal to the sum of the average thicknesses of each layer of the co-extruded film.

[0089] From the viewpoint of gas barrier properties, recyclability, and economic efficiency, the average thickness of the barrier resin layer (C) of the co-extruded film is preferably 0.2 μm or more and less than 30 μm. It is also preferable that the ratio of the average thickness of the barrier resin layer (C) to the average thickness of the co-extruded film is less than 25%. The average thickness of the barrier resin layer (C) is more preferably 0.4 μm or more and less than 15 μm, even more preferably 0.6 μm or more and less than 10 μm, and even more preferably 0.8 μm or more and less than 5 μm. The ratio of the average thickness of the barrier resin layer (C) to the average thickness of the co-extruded film is more preferably less than 20%, and even more preferably less than 15%.

[0090] The co-extruded film may be a substantially unstretched film, or a uniaxially or biaxially stretched film. If it is an unstretched film, the resulting paper container tends to have higher strength in low-temperature environments. If it is a stretched film, it tends to have higher gas barrier properties.

[0091] The co-extruded film is preferably stretched by at least 3 times or more but less than 12 times in at least one axial direction, and more preferably by at least 4 times or more but less than 10 times in at least one axial direction. Furthermore, the co-extruded film is also preferably stretched by at least 3 times or more but less than 12 times in each of two axial directions, and more preferably by at least 3.5 times or more but less than 10 times in each of two axial directions. By stretching the co-extruded film at such magnifications, the gas barrier properties of the multilayer structure can be further enhanced.

[0092] (Moisture-proof resin layer (F)) The multilayer structure of the present invention preferably further comprises a moisture-proof resin layer (F), separate from the moisture-proof resin layer (E) described above. The moisture-proof resin layer (F) mainly comprises polyethylene (f). By further comprising such a moisture-proof resin layer (F) in the multilayer structure, the moisture resistance and the strength of the resulting paper container in low-temperature environments can be further enhanced. The moisture-proof resin layer (F) may also be a heat-sealable layer for bonding moisture-proof resin layers (F) to each other, or to other layers by heat sealing. From the viewpoint of further enhancing the strength of the resulting paper container in low-temperature environments, the moisture-proof resin layer (F) may be the outermost layer in the multilayer structure. Furthermore, by making polyethylene (f) the main component of the moisture-proof resin layer (F), defects and discoloration during recycling are suppressed. In this specification, the moisture-proof resin layer provided on the side of the paper layer (A) opposite to the side where the inorganic vapor-deposited layer (B), etc., is provided (hereinafter also referred to as the "exposed surface side") shall be the moisture-proof resin layer (F). Furthermore, any moisture-proof resin layer different from the moisture-proof resin layer (E) that constitutes the co-extruded film shall be the moisture-proof resin layer (F). On the other hand, if there are multiple moisture-proof resin layers that constitute the co-extruded film, all of these moisture-proof resin layers shall be the moisture-proof resin layer (E). If a multilayer structure does not have the co-extruded film and has multiple moisture-proof resin layers (except in the case of the moisture-proof resin layer on the exposed surface side of the paper layer (A)), all of these moisture-proof resin layers shall be the moisture-proof resin layer (E).

[0093] The type, physical properties, specific form, and preferred form of polyethylene(f) are the same as those of polyethylene(e) described above, except for MFR. For example, the density of polyethylene(f) is 0.880 g / cm³. 3 More than 0.940g / cm 3The following is preferable. Furthermore, polyethylene(f) is preferably linear low-density polyethylene, low-density polyethylene, or a mixture thereof. The MFR (at 190°C, 2.16 kg load) of polyethylene(f) is preferably 0.4 g / 10 min to 30.0 g / 10 min, more preferably 0.8 g / 10 min to 20.0 g / min, and even more preferably 1.0 g / 10 min to 10.0 g / min.

[0094] The composition, average thickness, and other specific and preferred forms of the moisture-proof resin layer (F) are the same as those of the moisture-proof resin layer (E) described above. In one embodiment of the multilayer structure of the present invention, the moisture-proof resin layer (F) is preferably an unstretched layer. The moisture-proof resin layer (F) may be a stretched layer.

[0095] In the multilayer structure of the present invention, the position of the moisture-proof resin layer (F) is not particularly limited. However, it is preferable that the moisture-proof resin layer (F) is directly laminated to the co-extruded film. In the case of such a multilayer structure, in addition to being able to further increase the strength in low-temperature environments, the proportion of polyethylene-based resin used is increased, which tends to further reduce defects and discoloration when recycling. In the multilayer structure of this embodiment, for example, the moisture-proof resin layer (F) can be laminated by melt-extruding polyethylene (f) directly onto the surface of the moisture-proof resin layer (E) of the co-extruded film.

[0096] In addition, the moisture-proof resin layer (F) may be laminated on the surface of the moisture-proof resin layer (E) of the co-extruded film via another layer (e.g., an adhesive resin layer, another adhesive layer, etc.). In such a multilayer structure, the moisture-proof resin layer (F) can be laminated by dry lamination, sandwich lamination, etc., of the co-extruded film and a single-layer film of the moisture-proof resin layer (F).

[0097] Furthermore, the moisture-proof resin layer (F) may be laminated directly or via another layer on the side of the paper layer (A) opposite to the inorganic vapor-deposited layer (B). In such a multilayer structure, the moisture-proof resin layer (F) can be laminated by melt extrusion of polyethylene (f) onto the surface of the paper layer (A), dry lamination of the paper layer (A) or the multilayer structure containing the paper layer (A) with a single-layer film of the moisture-proof resin layer (F), sandwich lamination, etc.

[0098] (Other layers) The multilayer structure of the present invention may have layers other than the paper layer (A), inorganic vapor deposition layer (B), barrier resin layer (C), adhesive resin layer (D), moisture-proof resin layer (E), moisture-proof resin layer (F), and thermoplastic resin layer (X) described above. Other layers that the multilayer structure of the present invention may have include other thermoplastic resin layers, adhesive layers, printing layers, etc. However, the multilayer structure does not have a layer mainly composed of a resin with a melting point of 200°C or higher, or a metal layer with an average thickness of 1 μm or more. When a multilayer structure includes a layer mainly composed of a resin with a melting point of 200°C or higher (for example, a layer mainly composed of polyethylene terephthalate) and a metal layer with an average thickness of 1 μm or more (for example, a metal foil layer with an average thickness of 1 μm or more), defects are more likely to occur in recycled products during melt molding for recycling. Since the multilayer structure does not have such layers, defects are less likely to occur in recycled products, and it has excellent recyclability.

[0099] Furthermore, it is preferable that the multilayer structure of the present invention does not have an adhesive layer made of a curing type adhesive. By not having such an adhesive layer, drawbacks such as those during recycling are further suppressed.

[0100] (Layer composition, etc.) The multilayer structure of the present invention comprises a paper layer (A), an inorganic vapor-deposited layer (B), a barrier resin layer (C), an adhesive resin layer (D), and a moisture-proof resin layer (E). Furthermore, the inorganic vapor-deposited layer (B), the barrier resin layer (C), the adhesive resin layer (D), and the moisture-proof resin layer (E) are all directly laminated in this order. It is preferable that the multilayer structure has the paper layer (A), inorganic vapor-deposited layer (B), barrier resin layer (C), adhesive resin layer (D), and moisture-proof resin layer (E) in this order, particularly from the viewpoint of increasing strength in low-temperature environments. The multilayer structure may also have the paper layer (A), moisture-proof resin layer (E), adhesive resin layer (D), barrier resin layer (C), and inorganic vapor-deposited layer (B) in this order. The paper layer (A) and the inorganic vapor-deposited layer (B) or moisture-proof resin layer (E) may be directly laminated, but are usually laminated via other layers. Examples of interposed layers between the paper layer (A) and the inorganic vapor-deposited layer (B) or moisture-proof resin layer (E) include a thermoplastic resin layer (X) or other adhesive layers. The multilayer structure may also further include a moisture-proof resin layer (F).

[0101] The multilayer structure of the present invention preferably has a paper layer (A) on one surface. That is, in the multilayer structure, it is preferable that one of the outermost layers is a paper layer (A). However, when a paper container is formed from the multilayer structure, it is preferable that the surface where the paper layer (A) is exposed becomes the outer surface. When the multilayer structure has a paper layer (A) on its surface, it becomes easier to detect the paper, specifically by measuring the infrared spectrum using, for example, total internal reflection. For this reason, the paper recycling rate can be increased in such a multilayer structure.

[0102] The multilayer structure of the present invention may also preferably have a moisture-proof resin layer (E) or a moisture-proof resin layer (F) on one of its surfaces. That is, in the multilayer structure, it is preferable that one of the outermost layers is a moisture-proof resin layer (E) or a moisture-proof resin layer (F). When a paper container is formed from the multilayer structure, it is preferable that the surface on which the moisture-proof resin layer (E) or moisture-proof resin layer (F) is exposed becomes the inner surface. When the multilayer structure has a moisture-proof resin layer (E) or a moisture-proof resin layer (F) on its surface, these layers are bonded by heat sealing, making it possible to form a paper container with higher strength in low-temperature environments. Furthermore, when the multilayer structure has a moisture-proof resin layer (E) or a moisture-proof resin layer (F) on its surface, it becomes easier to detect polyethylene, specifically by measuring the infrared spectrum using, for example, total internal reflection. For this reason, the recycling rate of polyethylene can be increased in such a multilayer structure.

[0103] The multilayer structure of the present invention preferably has a paper layer (A) on one surface and a moisture-proof resin layer (E) or a moisture-proof resin layer (F) on the other surface. When a paper container is formed from the multilayer structure, it is preferable that the surface with the paper layer (A) exposed becomes the outer surface, and the surface with the moisture-proof resin layer (E) or moisture-proof resin layer (F) exposed becomes the inner surface.

[0104] The following are examples of specific layer configurations for the multilayer structure of the present invention. However, the layer configuration of the multilayer structure is not limited to the following configurations. In the following examples of layer configurations, " / " indicates that the layers are directly laminated. Also, "Ad" indicates any adhesive layer. The adhesive layer represented by Ad may be a layer mainly composed of an adhesive resin (a layer made of the same material as the adhesive resin layer (D)). (1) A / X / B / C / D / E (2) A / Ad / B / C / D / E (3) A / X / B / C / D / E / F (4) A / X / B / C / D / E / Ad / F (5) F / A / X / B / C / D / E (6) F / A / Ad / B / C / D / E (7) F / A / X / B / C / D / E / F (8) F / A / X / B / C / D / E / Ad / F (9) F / Ad / A / X / B / C / D / E (10) F / Ad / A / Ad / B / C / D / E (11) F / Ad / A / X / B / C / D / E / F (12) F / Ad / A / X / B / C / D / E / Ad / F (13) A / X / E / D / C / B / F (14) A / X / E / D / C / B / Ad / F (15) A / Ad / E / D / C / B / F (16) A / Ad / E / D / C / B / Ad / F (17) F / A / X / E / D / C / B / F (18) F / A / X / E / D / C / B / Ad / F (19)F / Ad / A / X / E / D / C / B / F (20)F / Ad / A / X / E / D / C / B / Ad / F (21) F / A / Ad / E / D / C / B / F (22) F / A / Ad / E / D / C / B / Ad / F (23) F / Ad / A / Ad / E / D / C / B / F (24) F / Ad / A / Ad / E / D / C / B / Ad / F

[0105] The lower limit of the mass ratio of the paper layer (A) in the multilayer structure of the present invention may be, for example, 0.40 or 0.50 of the total mass ratio of the multilayer structure, but 0.60 is preferred, 0.70 is more preferred, and 0.75 is even more preferred. By having a mass ratio of paper layer (A) of 0.95 or higher, the strength of the molded paper container in low-temperature environments can be further enhanced. On the other hand, the upper limit of the mass ratio of paper layer (A) is 0.95, 0.90 is more preferred, and 0.86 is even more preferred. By having a mass ratio of paper layer (A) of 0.95 or higher, the gas barrier properties and the strength of the molded paper container in low-temperature environments can be further enhanced.

[0106] The lower limit of the total average thickness ratio of the polyethylene resin-based layer in the portion of the multilayer structure of the present invention other than the paper layer (A) is preferably 0.75, more preferably 0.80, even more preferably 0.85, and even more preferably 0.90. By increasing the total average thickness ratio of the polyethylene resin-based layer in the portion of the multilayer structure other than the paper layer (A), it is possible to further suppress the occurrence of discoloration during recycling. The upper limit of the total average thickness ratio of the polyethylene resin-based layer in the portion of the structure other than the paper layer (A) is preferably 0.995, more preferably 0.99, and may also be 0.98. Examples of layers mainly composed of polyethylene resin include a moisture-proof resin layer (E), a moisture-proof resin layer (F), an adhesive resin layer (D) when the adhesive resin (d) is, for example, acid-modified polyethylene, and a thermoplastic resin layer (X) when the main component is polyethylene resin (polyethylene or modified polyethylene).

[0107] The lower limit of the total average thickness ratio of the layers mainly composed of resin having ethylene units in the parts of the multilayer structure of the present invention other than the paper layer (A) is preferably 0.95, more preferably 0.98, and even more preferably 0.99. By increasing the total average thickness ratio of the layers mainly composed of resin having ethylene units in the parts of the multilayer structure other than the paper layer (A), compatibility during recycling is improved, and the occurrence of defects and discoloration can be further suppressed. The upper limit of the total average thickness ratio of the layers mainly composed of resin having ethylene units in the parts of the structure other than the paper layer (A) may be, for example, 0.9999. Examples of layers mainly composed of resin having ethylene units include the polyethylene resin layer mentioned above, as well as a barrier resin layer (C).

[0108] The lower limit of the total average thickness ratio of layers mainly composed of thermoplastic resin with a melting point of less than 200°C in the parts of the multilayer structure of the present invention other than the paper layer (A) is preferably 0.95, more preferably 0.98, and even more preferably 0.99. By increasing the total average thickness ratio of thermoplastic resin with a melting point of less than 200°C in the parts other than the paper layer (A), the melt moldability during recycling is improved, and the occurrence of defects and discoloration can be further suppressed. The upper limit of the total average thickness ratio of layers mainly composed of thermoplastic resin with a melting point of less than 200°C in the parts other than the paper layer (A) may be, for example, 0.9999.

[0109] The lower limit of the average thickness of the multilayer structure of the present invention (average thickness of the entire multilayer structure) is preferably 150 μm, more preferably 200 μm, even more preferably 250 μm, and even more preferably greater than 300 μm. Having an average thickness of the multilayer structure equal to or greater than the lower limit allows for increased strength of the molded paper container in low-temperature environments. On the other hand, the upper limit of the average thickness of the multilayer structure is preferably 1,000 μm, but may also be 700 μm or 500 μm. Having an average thickness of the multilayer structure equal to or less than the upper limit allows for improved moldability.

[0110] In the multilayer structure of the present invention, the oxygen permeation rate measured under conditions of 20°C and 65%RH by the method described in JIS K 7126-2:2006 is 0.5 cc / (m³). 2 It is preferable that it be less than 0.1 cc / (m³) days·atm. 2 It is more preferable that the oxygen permeation rate is less than the above upper limit. Having an oxygen permeation rate below the above upper limit makes it particularly suitable for use as a molding material for paper containers, etc. On the other hand, the lower limit of this oxygen permeation rate is 0.001 cc / (m³). 2 It may also be 0.01cc / (m) 2 (・day・atm) is also acceptable.

[0111] In the multilayer structure of the present invention, the paper layer (A) is folded into quarters so that it faces outward from the moisture-proof resin layer (E), and a 5 kg load is applied from above and left to stand for 1 minute to perform the folding treatment. After that, the oxygen permeation rate under conditions of 20°C and 65% RH, measured by the method described in JIS K 7126-2:2006, is 1.0 cc / (m³). 2 It is preferable that it be less than 0.2 cc / (m³) days·atm. 2 It is more preferable that the oxygen permeability rate after bending is less than the above upper limit. If the oxygen permeability rate after bending is less than the above upper limit, it can be particularly suitable for use as a molding material for paper containers that are normally subjected to bending. On the other hand, the lower limit of the oxygen permeability rate after bending is 0.002 cc / (m³). 2 It may also be 0.02cc / (m) 2 (・day・atm) is also acceptable.

[0112] The multilayer structure of the present invention can be crushed for reuse, separated into a paper layer (A) and a portion other than the paper layer (A), and the portion other than the paper layer (A) can be used as a melt molding material. By using the portion other than the paper layer (A) of the multilayer structure as a melt molding material, a melt-molded product (recycled product) with fewer defects can be obtained. The portion other than the paper layer (A) of the multilayer structure can be used in combination with other melt molding materials (other recycled resins, unused resins, etc.). The separated paper layer (A) can also be reused.

[0113] The method for manufacturing the multilayer structure of the present invention is not particularly limited. For example, (1) a co-extruded film of a barrier resin layer (C), an adhesive resin layer (D), and a moisture-proof resin layer (E) is produced by co-extrusion. (2) A composite film is produced by providing an inorganic vapor deposition layer (B) on the side of the co-extruded film facing the barrier resin layer (C). (3) A multilayer structure is obtained by laminating a paper layer (A) and the composite film using known means such as sandwich lamination or dry lamination, such as so that the paper layer (A) and the inorganic vapor deposition layer (B) or moisture-proof resin layer (E) face each other. If the multilayer structure of the present invention further comprises a moisture-proof resin layer (F), the moisture-proof resin layer (F) can be provided by known methods such as melt extrusion or dry lamination.

[0114] Alternatively, for example, a composite film may be produced by first providing an inorganic vapor-deposited layer (B) on a single-layer film of a barrier resin layer (C), and then laminating an adhesive resin layer (D) and a moisture-proof resin layer (E). Or, a two-layer film of the inorganic vapor-deposited layer (B) and the barrier resin layer (C) may be bonded to a paper layer, and then laminating an adhesive resin layer (D) and a moisture-proof resin layer (E).

[0115] The multilayer structure of the present invention is suitably used as a molding material for paper containers. The use of the paper container is not particularly limited and may be a container for solids such as food, but it is preferably a container for liquids. The multilayer structure may also be used for purposes other than as a molding material for paper containers.

[0116] <Liquid paper containers> The liquid paper container of the present invention is a paper container formed by molding the multilayer structure of the present invention. The paper container has high gas barrier properties even in the folded portion, possesses sufficient strength even in low-temperature environments, and suppresses the occurrence of defects during recycling. The liquid paper container is suitably used as a container for various liquids other than food, such as beverages like milk and juice, liquid foods like soup, alcoholic beverages like sake and shochu.

[0117] The liquid paper container of the present invention is formed by folding the multilayer structure of the present invention into, for example, a box shape and bonding the overlapping portions by heat sealing or the like. In the liquid paper container, it is preferable that the paper layer (A) is located on the outer surface. Furthermore, it is preferable that the moisture-proof resin layer (E) or moisture-proof resin layer (F) is located on the inner surface.

[0118] The shape of the liquid paper container of the present invention is not limited to a box shape, but may be other shapes (e.g., a bag shape). The liquid paper container may be bonded by a method other than heat sealing, and may have parts bonded by heat sealing and parts bonded by other methods. Furthermore, the liquid paper container may further have components other than the multilayer structure of the present invention. [Examples]

[0119] The present invention will be described in detail below with reference to examples, but the present invention is not limited to these examples.

[0120] [Example 1] (1) Preparation of EVOH(c)-containing resin composition for barrier resin layer (C) EVOH(c-1) (containing 32 mol% ethylene units, 99.99 mol% saponification degree, MFR (190°C, 2.16 kg load) 1.6 g / 10 min, containing 220 ppm sodium acetate (sodium ion equivalent), 30 ppm phosphate ions (phosphate root equivalent), and 150 ppm boric acid (boron element equivalent), and no polyvalent metal ions) and magnesium stearate (Mg-St) were melt-kneaded to obtain resin composition pellets for the barrier resin layer (C) by melt-kneading them so that the magnesium ion content in the resulting resin composition was 50 ppm. The extruder used for melt-kneading was a twin-screw extruder with D (mm) = 25, and a fully meshed co-direction screw with L / D = 25 was used. The resin temperature was set to 220°C.

[0121] (2) Resin composition containing adhesive resin (d) for adhesive resin layer (D) Admer® NF518, a maleic anhydride-modified polyethylene manufactured by Mitsui Chemicals, Inc. (MFR (190℃, 2.16kg load) 3.1g / 10min, density 0.91g / cm³) 3 A solution with an acid value of 1.8 mg KOH / g was used as the adhesive resin (d-1). Pellets of this adhesive resin (d-1) were used as resin composition pellets for the adhesive resin layer (D).

[0122] (3) Polyethylene (e)-containing resin composition for moisture-proof resin layer (E) Low-density polyethylene (LDPE) "INNATE (trademark) TF80" manufactured by DOW Corporation (MFR (190℃, 2.16kg load) 1.6g / 10min, density 0.926g / cm³) 3 The pellets of ) were made of polyethylene (e-1). These polyethylene (e-1) pellets were used as is as resin composition pellets for the moisture-proof resin layer (E).

[0123] (4) Preparation of co-extruded film Using the resin composition pellets described in (1) to (3) above, co-extruded films with a layer thickness and layer structure of C / D / E = 4 μm / 4 μm / 32 μm = EVOH4 / tie4 / PE32 were produced using a co-extrusion film manufacturing facility. "tie" represents the adhesive resin. The average thickness of the layers is also simply called the layer thickness. All extruders were single-screw extruders with D (mm) = 30, and full-flight screws with L / D = 28 and a compression ratio of 3.0 were used. A 350 mm wide feed block laminated T-die was used as the die. The temperature conditions at this time are shown below. Extrusion temperature of barrier resin layer (C): Feed unit / compression unit / metering unit / adapter = 175 / 220 / 220 / 220℃ Extrusion temperature of adhesive resin layer (D): Feeding unit / Compression unit / Measuring unit / Adapter = 175 / 220 / 220 / 220℃ Extrusion temperature of moisture-proof resin layer (E): Feed unit / compression unit / metering unit / adapter = 175 / 220 / 220 / 220℃ Die temperature: 220℃ Cooling roll temperature: 80℃

[0124] (5) Preparation of composite film A 50 nm thick aluminum metal vapor-deposited layer (inorganic vapor-deposited layer (B)) was laminated onto the surface of the barrier resin layer (C) of the co-extruded film obtained in (4) above by a known vacuum deposition method, thereby producing a composite film having a layer thickness and layer structure of B / C / D / E = 50 nm / 4 μm / 4 μm / 32 μm = Al (50 nm) / EVOH4 / tie4 / PE32.

[0125] (6) Fabrication of multilayer structures The paper layer (A) has a basis weight of 250 g / m². 2 White cardboard was prepared. In addition, as the resin for extrusion lamination (thermoplastic resin), linear low-density polyethylene (LLDPE) "LUMITAC(trademark) BL 600K" manufactured by Tosoh Corporation (MFR (190℃, 2.16kg load) 21g / 10min, density 0.898g / cm³) was used. 3 I prepared ). The white cardboard is fed from the first paper feed section of the extrusion laminating equipment, and the composite film obtained in (5) is fed from the second paper feed section. Between them, the linear low-density polyethylene is extruded at 300°C to laminate a linear low-density polyethylene layer (thermoplastic resin layer (X)) with an average thickness of 20 μm, resulting in A / X / B / C / D / E = 250 g / m². 2 A multilayer structure was fabricated with layer thicknesses and configurations of paper / PE20 / Al(50nm) / EVOH4 / tie4 / PE32, with layers of 20μm / 50nm / 4μm / 4μm / 32μm.

[0126] Furthermore, the resins constituting the barrier resin layer (C), adhesive resin layer (D), moisture-proof resin layer (E), and thermoplastic resin layer (X) in the obtained multilayer structure all have a predetermined MFR at 190°C. Therefore, it is clear that the melting points of these resins are below 200°C. The same applies to the other examples described later.

[0127] (7) Oxygen permeability (OTR) of multilayer structures For the multilayer structure obtained in (6) above, the oxygen permeation rate was measured according to the method described in JIS K 7126-2 (isobaric method; 2006), with the paper layer on the oxygen supply side and the composite film on the carrier gas side. Specifically, using an oxygen permeation rate measuring device (MOCON OX-TRAN2 / 21 manufactured by Modern Control Co., Ltd.), the oxygen permeation rate (unit: cc / (m³)) was measured under conditions of a temperature of 20°C, humidity of 65%RH on the oxygen supply side and 65%RH on the carrier gas side, oxygen pressure of 1 atm, and carrier gas pressure of 1 atm. 2 The gas barrier properties were measured (day·atm) and judged according to the following criteria. Nitrogen gas containing 2 volume% hydrogen gas was used as the carrier gas. The results are shown in Table 2. In cases A to D, it was determined that the gas barrier properties were high even without bending treatment. Judgment criteria A: 0.05cc / (m 2 Less than (day / atm) B: 0.05cc / (m 2 ·day · atm) or more, 0.1cc / (m 2 Less than (day / atm) C: 0.1cc / (m 2 ·day · atm) or more, 0.5cc / (m 2 Less than (day / atm) D: 0.5cc / (m 2 ·day · atm) or more, 2.0cc / (m 2 Less than (day / atm) E: 2.0cc / (m 2 ·day · atm) or more

[0128] (8) Oxygen permeability rate of multilayer structures after bending (OTR after bending) The multilayer structure obtained in (6) above was cut into 10 cm squares, folded into quarters so that the paper layer (A) was on the outside relative to the moisture-proof resin layer (E), and a 5 kg load was applied from above and left for 1 minute to perform the folding treatment. After the folding treatment, the 2 kg load was removed and the folds were opened. The oxygen permeation rate of the multilayer structure was measured according to the method described in JIS K 7126-2 (isobaric method; 2006), with the paper layer (A) as the oxygen supply side and the composite film as the carrier gas side. Specifically, an oxygen permeation rate measuring device (Modern Control Co., Ltd. "MOCON OX-TRAN2 / 21") was used, and the oxygen permeation rate (unit: cc / (m)) was measured under conditions of a temperature of 20°C, humidity of 65% RH on the oxygen supply side and 65% RH on the carrier gas side, oxygen pressure of 1 atm, and carrier gas pressure of 1 atm. 2 The gas barrier properties were measured (day·atm) and judged according to the following criteria. Nitrogen gas containing 2 volume% hydrogen gas was used as the carrier gas. The results are shown in Table 2. In cases A to D, it was determined that the gas barrier properties were high in the state after the bending process. Judgment criteria A: 0.1cc / (m 2 Less than (day / atm) B: 0.1cc / (m 2 ·day · atm) or more, 0.2cc / (m 2 Less than (day / atm) C: 0.2cc / (m 2 ·day · atm) or more, 1.0cc / (m 2 Less than (day / atm) D: 1.0cc / (m 2 ·day · atm) or more, 4.0cc / (m 2 Less than (day / atm) E: 4.0cc / (m 2 ·day · atm) or more

[0129] (9) Drop rupture resistance of multilayer structures (drop strength (low temperature)) Two 12cm x 24cm pieces of the multilayer structure obtained in (6) above were cut out and stacked with the paper layers (A) facing outwards, and three sides were heat-sealed with a width of 5mm. Next, 500g of water was filled into the opening, and the remaining sides were heat-sealed to create a water-filled paper container. This water-filled paper container was dropped three times in an upright direction from a height of 1m at 5℃ to observe whether or not there was any water leakage. Ten water-filled paper containers were made using the above method, and these ten were evaluated and judged according to the following criteria. The results are shown in Table 2. In cases A to D, it was determined that a paper container with sufficient strength can be formed even in a low-temperature environment. Judgment criteria A: No water leaks were observed. B: One or two water leaks were observed. C: Three to five water leaks were observed. D: Six to eight water leaks were observed. E: 9 to 10 water leaks were observed.

[0130] (10) Paper detection For the multilayer structure obtained in (6) above, infrared spectra were measured on both sides using total internal reflection. If paper was detected on either side, it was considered a pass (OK), and if no paper was detected on either side, it was considered a fail (NG). The results are shown in Table 2.

[0131] (11) Polyethylene detectability For the multilayer structure obtained in (6) above, the infrared spectrum was measured on both sides using total internal reflection. If polyethylene was detected on either side, it was considered a pass (OK), and if paper was not detected on either side, it was considered a fail (NG). The results are shown in Table 2.

[0132] (12) Recyclability of parts other than the paper layer separated from the multilayer structure The multilayer structure obtained in (6) above was crushed to a size of 4 mm square or less, and stirred in a 90°C sodium hydroxide aqueous solution (1 mol / L) for 30 minutes to remove the paper layer (A) from the multilayer structure. The portion consisting of the parts other than the paper layer (A) that were suspended in the aqueous solution was recovered, washed with room temperature water, and dried at 60°C for 24 hours. This recovered material was mixed with low-density polyethylene resin (LDPE) "Novatec (trademark) LD LJ400" manufactured by Nippon Polyethylene Co., Ltd. (MFR (190°C, 2.16 kg load) 1.5 g / 10 min, density 0.921 g / cm³). 3 A single-layer film with a thickness of 50 μm was obtained by blending the two materials in a mass ratio (recovered material / low-density polyethylene resin) of 40 / 60 and performing single-layer film formation under the extrusion conditions shown below. As a control, a single-layer film with a thickness of 50 μm was similarly obtained using only the low-density polyethylene resin. The extruder was a single-screw extruder with D (mm) = 20, and a full-flight screw with L / D = 20 and a compression ratio of 3.5 was used. A 300 mm wide T-die was used as the die. The thickness of the single-layer film was adjusted by appropriately changing the screw rotation speed and the take-up roll speed. The temperature conditions at this time are shown below. Extrusion temperature: Feed unit / Compression unit / Measuring unit / Adapter = 175 / 220 / 220 / 220℃ Die temperature: 220℃ Cooling roll temperature: 80℃ The obtained single-layer films were visually evaluated for coloration and defects, and judged according to the following criteria. The results are shown in Table 2. In cases A to D, it was determined that the occurrence of coloration or defects during recycling was suppressed. Coloring judgment: Criteria A: Compared to the control, the degree of hue change was small. B: Mild discoloration was observed compared to the control. C: Moderate discoloration was observed compared to the control group. D: Significant discoloration was observed compared to the control group. E: Compared to the control group, significant discoloration was observed, and unevenness was also seen. Criteria for determining defects: A: The amount of substance remained almost unchanged compared to the control group. B: Compared to the control, there was a slightly larger amount of small particles. C: Compared to the control group, there was a greater quantity of small particles. D: There was a greater quantity of large objects compared to the control group. E: Compared to the control group, the amount of large particles was significantly higher.

[0133] [Example 2] Resin composition pellets, co-extruded films, composite films, and multilayer structures were prepared in the same manner as in Example 1, except that EVOH(c-2) (ethylene unit content 27 mol%, degree of saponification 99.99 mol%, MFR (210℃, 2.16 kg load) 4.0 g / 10 min, containing 220 ppm sodium acetate in terms of sodium ions, 30 ppm phosphate ions in terms of phosphate roots, and 150 ppm boric acid in terms of boron elements, and not containing polyvalent metal ions) was used instead of EVOH(c-1), and various measurements and evaluations were performed. The results are shown in Table 2.

[0134] [Example 3] Resin composition pellets, co-extruded films, composite films, and multilayer structures were prepared in the same manner as in Example 1, except that EVOH(c-3) (ethylene unit content 44 mol%, degree of saponification 99.99 mol%, MFR (190°C, 2.16 kg load) 5.7 g / 10 min, containing 220 ppm sodium acetate in terms of sodium ions, 30 ppm phosphate ions in terms of phosphate roots, and no polyvalent metal ions) was used instead of EVOH(c-1). Various measurements and evaluations were then performed. The results are shown in Table 2.

[0135] [Example 4] Resin composition pellets, co-extruded films, composite films, and multilayer structures were prepared in the same manner as in Example 1, except that EVOH(c-2) and EVOH(c-3) were mixed (dry blended) in a mass ratio of 75 / 25 instead of EVOH(c-1), and various measurements and evaluations were performed. The results are shown in Table 2.

[0136] [Example 5] Resin composition pellets, co-extruded films, composite films, and multilayer structures were prepared in the same manner as in Example 1, except that the average thickness of the aluminum metal vapor-deposited layer was changed to 100 nm. Various measurements and evaluations were then performed. The results are shown in Table 2.

[0137] [Example 6] Resin composition pellets, co-extruded films, composite films, and multilayer structures were prepared in the same manner as in Example 1, except that the aluminum metal vapor-deposited layer was replaced with an alumina (AlOx) vapor-deposited layer. Various measurements and evaluations were then performed. The results are shown in Table 2.

[0138] [Example 7] Resin composition pellets, co-extruded films, composite films, and multilayer structures were prepared in the same manner as in Example 1, except that the aluminum metal vapor-deposited layer was replaced with a silica (SiOx) vapor-deposited layer. Various measurements and evaluations were then performed. The results are shown in Table 2.

[0139] [Example 8] Resin composition pellets, co-extruded films, composite films, and multilayer structures were prepared in the same manner as in Example 1, except that magnesium stearate was not used, and various measurements and evaluations were performed. The results are shown in Table 2.

[0140] [Examples 9-10] Except for changing the amount of magnesium stearate mixed with EVOH(c-1) as shown in Table 1 in terms of magnesium ions, resin composition pellets, co-extruded films, composite films, and multilayer structures were prepared in the same manner as in Example 1, and various measurements and evaluations were performed. The results are shown in Table 2.

[0141] [Examples 11-12] Except for changing the magnesium stearate mixed with EVOH(c-1) to calcium stearate (Ca-St) (Example 11) and zinc stearate (Zn-St) (Example 12), resin composition pellets, co-extruded films, composite films, and multilayer structures were prepared in the same manner as in Example 1, and various measurements and evaluations were performed. The results are shown in Table 2.

[0142] [Example 13] Instead of polyethylene (e-1), use polyethylene (e-2) (linear low-density polyethylene (mLLDPE) "Evolu™ SP1510" polymerized with a metallocene catalyst manufactured by Prime Polymer Co., Ltd. (MFR (190℃, 2.16kg load) 1.0g / 10min, density 0.915g / cm³) 3 Resin composition pellets, co-extruded films, composite films, and multilayer structures were prepared in the same manner as in Example 1, except that ) was used, and various measurements and evaluations were performed. The results are shown in Table 2.

[0143] [Example 14] Instead of polyethylene (e-1), use polyethylene (e-3) (high-density polyethylene (HDPE) "Novatec (trademark) HD ​​HY540" manufactured by Nippon Polyethylene Co., Ltd. (MFR (190℃, 2.16kg load) 1.0g / 10min, density 0.960g / cm³) 3 Resin composition pellets, co-extruded films, composite films, and multilayer structures were prepared in the same manner as in Example 1, except that ) was used, and various measurements and evaluations were performed. The results are shown in Table 2.

[0144] [Example 15] Except for changing the average thickness of the barrier resin layer (C) to 12 μm, resin composition pellets, co-extruded films, composite films, and multilayer structures were prepared in the same manner as in Example 1, and various measurements and evaluations were performed. The results are shown in Table 2.

[0145] [Example 16] Except for changing the average thickness of the moisture-proof resin layer (E) to 52 μm, resin composition pellets, co-extruded films, composite films, and multilayer structures were prepared in the same manner as in Example 1, and various measurements and evaluations were performed. The results are shown in Table 2.

[0146] [Example 17] Resin composition pellets, co-extruded films, composite films, and multilayer structures were prepared in the same manner as in Example 1, except that the paper layer and composite film were laminated by a known dry lamination method instead of extrusion lamination, and various measurements and evaluations were performed. The results are shown in Table 2. A two-component reactive polyurethane adhesive was used as the adhesive for dry lamination, and it was used so that the average thickness after drying was 4 μm.

[0147] [Example 18] In the same procedure as in Example 1, a moisture-proof resin layer (F) was applied to the exposed surface of the paper layer (A) of the multilayer structure, using "LUMITAC® BL 600K" linear low-density polyethylene (LLDPE) manufactured by Tosoh Corporation (MFR (190℃, 2.16kg load) 21g / 10min, density 0.898g / cm³). 3 A multilayer structure was fabricated by extruding () at 300°C to laminate linear low-density polyethylene layers with an average thickness of 30 μm, and various measurements and evaluations were performed. The results are shown in Table 2.

[0148] [Example 19] For the preparation of the co-extruded film, a co-extruded film with a layer thickness and layer structure of C / D / E = 5 μm / 5 μm / 115 μm = EVOH5 / tie5 / PE115 was prepared, and then stretched five times in the longitudinal direction to produce a stretched co-extruded film of 1 μm / 1 μm / 23 μm = EVOH1 / tie1 / PE23. Except for using this co-extruded film, resin composition pellets, co-extruded films, composite films, and multilayer structures were prepared in the same manner as in Example 1, and various measurements and evaluations were performed. The results are shown in Table 2.

[0149] [Example 20] Instead of EVOH(c-1), EVOH(c-4) (ethylene unit content 44 mol%, degree of saponification 99.99 mol%, degree of epoxypropane modification 4.6 mol%, MFR (190℃, 2.16 kg load) 5.6 g / 10 min, containing sodium acetate at 220 ppm in sodium ion equivalent, phosphate ions at 30 ppm in phosphate root equivalent, boric acid at 150 ppm in boron element equivalent, and zinc acetate at 30 ppm in zinc ion equivalent) was used. Furthermore, as a co-extruded film, a co-extruded film with a layer thickness and layer structure of C / D / E = 32 μm / 32 μm / 736 μm = EVOH32 / tie32 / PE736 was prepared. This film was stretched four times in the longitudinal direction and then eight times in the shortening direction to produce a stretched co-extruded film of 1 μm / 1 μm / 32 μm = EVOH1 / tie1 / PE32, and this co-extruded film was used. Except for these points, resin composition pellets, co-extruded films, composite films, and multilayer structures were prepared in the same manner as in Example 1, and various measurements and evaluations were performed. The results are shown in Table 2.

[0150] [Example 21] In the same procedure as in Example 20, the moisture-proof resin layer (E) of the multilayer structure was prepared on the exposed surface of the moisture-proof resin layer (F) using linear low-density polyethylene (LLDPE) "LUMITAC™ BL 600K" manufactured by Tosoh Corporation (MFR (190℃, 2.16kg load) 21g / 10min, density 0.898g / cm³). 3 A multilayer structure was fabricated by extruding () at 300°C to laminate linear low-density polyethylene layers with an average thickness of 30 μm, and various measurements and evaluations were performed. The results are shown in Table 2.

[0151] [Example 22] Paper layer (A) with a basis weight of 50 g / m² 2 Except for using white paper, resin composition pellets, co-extruded films, composite films, and multilayer structures were prepared in the same manner as in Example 1, and various measurements and evaluations were performed. The results are shown in Table 2.

[0152] [Example 23] Paper layer (A) with a basis weight of 80 g / m² 2Except for using white paper, resin composition pellets, co-extruded films, composite films, and multilayer structures were prepared in the same manner as in Example 1, and various measurements and evaluations were performed. The results are shown in Table 2.

[0153] [Example 24] Paper layer (A) with a basis weight of 150 g / m² 2 Except for using white paper, resin composition pellets, co-extruded films, composite films, and multilayer structures were prepared in the same manner as in Example 1, and various measurements and evaluations were performed. The results are shown in Table 2.

[0154] [Example 25] Resin composition pellets, co-extruded films, composite films, and multilayer structures were prepared in the same manner as in Example 21, except that a moisture-proof resin layer (E) and a paper layer (A) of the composite film were laminated via a thermoplastic resin layer (X), and a moisture-proof resin layer (F) was provided on the exposed inorganic vapor-deposited layer (B) during the fabrication of the multilayer structure. Various measurements and evaluations were then performed. The results are shown in Table 2.

[0155] [Comparative Example 1] Resin composition pellets, composite films, and multilayer structures were prepared in the same manner as in Example 1, except that the following composite film was prepared and used instead of the composite film prepared in Example 1, and various measurements and evaluations were performed. A single-layer film of a moisture-proof resin layer (E) with an average thickness of 40 μm was used without laminating the barrier resin layer (C) and adhesive resin layer (D). Corona discharge treatment was performed on one side of the moisture-proof resin layer (E) using a known method, and an aluminum metal vapor deposition layer was laminated on the corona-discharged surface to prepare the composite film. The results are shown in Table 2.

[0156] [Comparative Example 2] Resin composition pellets and multilayer structures were prepared in the same manner as in Example 1, except that a single-layer film of a moisture-proof resin layer (E) with an average thickness of 40 μm was used instead of a composite film, without laminating the barrier resin layer (C), adhesive resin layer (D), and aluminum metal vapor deposition layer. Various measurements and evaluations were then performed. The results are shown in Table 2.

[0157] [Comparative Example 3] Resin composition pellets, co-extruded films, and multilayer structures were prepared in the same manner as in Example 1, except that an aluminum metal vapor deposition layer was not laminated. Various measurements and evaluations were then performed. The results are shown in Table 2.

[0158] [Comparative Example 4] Resin composition pellets, composite films, and multilayer structures were prepared in the same manner as in Example 21, except that Toray Industries, Inc.'s biaxially oriented polyethylene terephthalate film "Lumirror (trademark) P60" (PET, melting point 256°C, average thickness 12 μm) was used instead of co-extruded film, corona discharge treatment was performed on both sides of the PET using a known method, an aluminum metal vapor deposition layer was laminated onto one side of the corona discharge-treated PET, and a moisture-proof resin layer (F) was laminated onto the non-vapor-deposited side of the PET. Various measurements and evaluations were then performed. The results are shown in Table 2.

[0159] [Comparative Example 5] Instead of adhesive resin (d-1), use maleic anhydride-modified polypropylene "Admer (trademark) QF551" manufactured by Mitsui Chemicals, Inc. (MFR (230℃, 2.16kg load) 5.7g / 10min, density 0.89g / cm³) 3 ) is replaced with polypropylene "Novatec (trademark) PP EA7AD" manufactured by Nippon Polypropylene Co., Ltd. (MFR (230℃, 2.16kg load) 1.4g / 10min, density 0.90g / cm³) instead of polyethylene (e-1). 3 Instead of linear low-density polyethylene, the thermoplastic resin layer (X) uses polypropylene "Novatec (trademark) PP FL03H" manufactured by Nippon Polypropylene Co., Ltd. (MFR (230℃, 2.16kg load) 26g / 10min, density 0.90g / cm³) 3 Except for the use of ), resin composition pellets, co-extruded films, composite films, and multilayer structures were prepared in the same manner as in Example 1, and various measurements and evaluations were performed. The results are shown in Table 2.

[0160] [Comparative Example 6] On the exposed surface of the moisture-proof resin layer (E), a moisture-proof resin layer (F) made of linear low-density polyethylene (LLDPE) "LUMITAC (trademark) BL 600K" manufactured by Tosoh Corporation is used (MFR (190℃, 2.16kg load) 21g / 10min, density 0.898g / cm³). 3 Resin composition pellets, co-extruded films, composite films, and multilayer structures were prepared in the same manner as in Comparative Example 5, except that the material was extruded at 300°C to laminate a linear low-density polyethylene layer with an average thickness of 30 μm. Various measurements and evaluations were then performed. The results are shown in Table 2.

[0161] Table 1 shows the type and basis weight of the paper layer (A) in each multilayer structure, the type and average thickness of the material constituting the inorganic vapor deposition layer (B), the type and ethylene unit content of the resin constituting the barrier resin layer (C), and the type and content of polyvalent metal ions, the type and density of the resin constituting the moisture-proof resin layer (E), and the type and density of the resin constituting the moisture-proof resin layer (F). Table 2 shows the layer composition and average thickness of each layer in each multilayer structure, the stretching ratio of the co-extruded film (MD×TD), the paper layer ratio (mass ratio of the paper layer to the entire multilayer structure), and the PE ratio other than the paper layer (total average thickness ratio of layers mainly composed of polyethylene resin in the parts other than the paper layer), along with the evaluation results.

[0162] [Table 1]

[0163] [Table 2]

[0164] As shown in Table 2, each of the multilayer structures in Examples 1 to 25 exhibited high gas barrier properties both before and after bending, enabling the formation of paper containers with sufficient strength even in low-temperature environments, and confirming that the occurrence of defects during recycling was suppressed. [Industrial applicability]

[0165] The multilayer structure of the present invention can be suitably used as a molding material for paper containers such as liquid paper containers.

Claims

1. It has a paper layer (A), an inorganic vapor deposition layer (B), a barrier resin layer (C), an adhesive resin layer (D), and a moisture-proof resin layer (E), The inorganic vapor-deposited layer (B), barrier resin layer (C), adhesive resin layer (D), and moisture-proof resin layer (E) are all directly laminated in this order. The average thickness of the inorganic vapor-deposited layer (B) is between 5 nm and 200 nm. The barrier resin layer (C) mainly contains an ethylene-vinyl alcohol copolymer (c) with an ethylene unit content of 20 mol% to 50 mol% and a degree of saponification of 90 mol% or more. The adhesive resin layer (D) contains adhesive resin (d) as its main component, The moisture-proof resin layer (E) contains polyethylene (e) as its main component. It does not have a layer containing a resin with a melting point of 200°C or higher as its main component, nor a metal layer with an average thickness of 1 μm or more. The paper layer (A) was folded into quarters so that it faced outward from the moisture-proof resin layer (E), and a 5 kg load was applied from above and left undisturbed for 1 minute to perform the bending treatment. After that, the oxygen permeation rate under conditions of 20°C and 65% RH, as measured by the method described in JIS K 7126-2:2006, was 1.0 cc / (m³). ２ A multilayer structure that is less than ・day・atm.

2. The multilayer structure according to claim 1, further comprising a thermoplastic resin layer (X) interposed between a paper layer (A) and an inorganic vapor-deposited layer (B) or a moisture-proof resin layer (E).

3. A multilayer structure according to claim 1 or 2, comprising a paper layer (A), an inorganic vapor deposition layer (B), a barrier resin layer (C), an adhesive resin layer (D), and a moisture-proof resin layer (E) in this order.

4. The multilayer structure according to claim 1 or 2, wherein the adhesive resin (d) is acid-modified polyethylene.

5. The multilayer structure according to claim 1 or 2, wherein the inorganic vapor deposition layer (B) is a metal vapor deposition layer mainly composed of aluminum or an inorganic oxide vapor deposition layer mainly composed of alumina or silica.

6. The multilayer structure according to claim 1 or 2, wherein the ethylene-vinyl alcohol copolymer (c) comprises two or more ethylene-vinyl alcohol copolymers with different ethylene unit content.

7. The density of polyethylene (e) is 0.880 g / cm³. ３ 0.940g / cm or more ３ The following: The multilayer structure according to claim 1 or 2, wherein polyethylene (e) is linear low-density polyethylene, low-density polyethylene, or a mixture thereof.

8. The laminate of the barrier resin layer (C), adhesive resin layer (D), and moisture-proof resin layer (E) is a co-extruded film. The average thickness of the co-extruded film is 8 μm or more and 120 μm or less. The multilayer structure according to claim 1 or 2, wherein an inorganic vapor deposition layer (B) is provided on the barrier resin layer (C) side of the co-extruded film.

9. The multilayer structure according to claim 8, wherein the average thickness of the barrier resin layer (C) is 0.2 μm or more and less than 30 μm, and the ratio of the average thickness of the barrier resin layer (C) to the average thickness of the co-extruded film is less than 25%.

10. The multilayer structure according to claim 8, wherein the co-extruded film is substantially unstretched.

11. The multilayer structure according to claim 8, wherein the co-extruded film is stretched by at least three times and less than twelve times in at least one axial direction.

12. The multilayer structure according to claim 8, wherein the co-extruded film is stretched by three times or more but less than twelve times in each of the two axial directions.

13. The multilayer structure according to claim 8, further comprising a moisture-proof resin layer (F) mainly composed of polyethylene (f).

14. The density of polyethylene (f) is 0.880 g / cm³. ３ 0.940g / cm or more ３ The following: The multilayer structure according to claim 13, wherein polyethylene (f) is linear low-density polyethylene, low-density polyethylene, or a mixture thereof.

15. The multilayer structure according to claim 13, wherein a moisture-proof resin layer (F) is directly laminated onto the co-extruded film.

16. A multilayer structure according to claim 1 or 2, which does not have an adhesive layer made of a curing type adhesive.

17. The basis weight of the paper layer (A) is 200 g / m². ２ More than 400g / m ２ A multilayer structure according to claim 1 or 2, wherein the multilayer structure is less than [amount missing].

18. The multilayer structure according to claim 1 or 2, wherein the mass ratio of the paper layer (A) is 0.60 or more of the total mass of the multilayer structure.

19. The multilayer structure according to claim 1 or 2, wherein the total average thickness ratio of the layers mainly composed of polyethylene resin in the portion other than the paper layer (A) is 0.75 or more.

20. The multilayer structure according to claim 1 or 2, wherein the total average thickness ratio of layers mainly composed of resin having ethylene units in the portion other than the paper layer (A) is 0.95 or more.

21. A multilayer structure according to claim 1 or 2, having a paper layer (A) on its surface.

22. The oxygen permeation rate measured under conditions of 20°C and 65% RH by the method described in JIS K 7126-2:2006 was 0.5 cc / (m³). ２ A multilayer structure according to claim 1 or 2, wherein the temperature is less than 1 / day atm.

23. A liquid paper container formed by molding a multilayer structure according to claim 1 or 2.

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