Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B32—LAYERED PRODUCTS
  • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
  • B32B27/00—Layered products comprising a layer of synthetic resin
  • B32B27/06—Layered products comprising a layer of synthetic resin as the main or only constituent of a layer, which is next to another layer of the same or of a different material
  • B32B27/10—Layered products comprising a layer of synthetic resin as the main or only constituent of a layer, which is next to another layer of the same or of a different material of paper or cardboard
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B32—LAYERED PRODUCTS
  • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
  • B32B27/00—Layered products comprising a layer of synthetic resin
  • B32B27/28—Layered products comprising a layer of synthetic resin comprising synthetic resins not wholly covered by any one of the sub-groups B32B27/30 - B32B27/42
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B32—LAYERED PRODUCTS
  • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
  • B32B9/00—Layered products comprising a layer of a particular substance not covered by groups B32B11/00 - B32B29/00

Definitions

• the present invention relates to a multi-layer structure and a paper container for liquids.
• Paper containers are widely used as containers for storing beverages such as milk and juice, liquid foods such as soup, alcoholic beverages such as sake and shochu, and various other non-food liquids.
• the materials used for paper containers are generally multilayer structures in which a resin layer, a vapor deposition layer, metal foil, etc. are laminated to a paper layer.
• Patent Document 1 describes a paper container formed from a multilayer structure in which a synthetic resin layer, etc. is laminated on one side of a base material mainly made of a paper layer, and an intermediate layer made of linear low-density polyethylene resin, a barrier layer, and a sealant layer are laminated in this order on the other side of the base material.
• the barrier layer of the multilayer structure in Patent Document 1 uses a vapor deposition film in which an inorganic substance is vapor-deposited on a polyethylene terephthalate resin film.
• Paper containers that hold beverages and other products are required to have high gas barrier properties in order to maintain quality.
• the gas barrier properties are easily reduced due to pinholes occurring at the bent parts.
• the containers must be strong enough to withstand vibrations, dropping, etc., and not leak from heat-sealed parts.
• packaging materials such as paper containers are desired to be materials that are easy to recover and reuse (high recyclability).
• the difference in the melting temperature of the resin, the crosslinking reaction of the resin, etc. may cause defects in the resulting recycled product (melt molded product), resulting in a deterioration in appearance and quality.
• the present invention was made based on these circumstances, and its purpose is to provide a multilayer structure that has high gas barrier properties both before and after folding, can be used to form a paper container with sufficient strength even in a low-temperature environment, and suppresses the occurrence of defects during recycling, and a liquid paper container using such a multilayer structure.
• a multilayer structure having 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 which the inorganic vapor deposition 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, the inorganic vapor deposition layer (B) has an average thickness of 5 nm or more and 200 nm or less, the barrier resin layer (C) contains, as a main component, an ethylene-vinyl alcohol copolymer (c) having an ethylene unit content of 20 mol % or more and 50 mol % or less and a saponification degree of 90 mol % or more, the adhesive resin layer (D) contains, as a main component, an adhesive resin (d), and the moisture-proof resin layer (E) contains, as a main component, polyethylene (e), and does not have a layer
• the present invention provides a multilayer structure that has high gas barrier properties both before and after folding, can be used to form a paper container with sufficient strength even in a low-temperature environment, and reduces defects during recycling, and can provide a paper container for liquids that uses such a multilayer structure.
• the multilayer structure of the present invention 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 deposition 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, the inorganic vapor deposition layer (B) has an average thickness of 5 nm to 200 nm, the barrier resin layer (C) contains as a main component an ethylene-vinyl alcohol copolymer (c) having an ethylene unit content of 20 mol % to 50 mol % and a saponification degree of 90 mol % or more, the adhesive resin layer (D) contains as a main component an adhesive resin (d), and the moisture-proof resin layer (E) contains as a main component polyethylene (e), and does not contain a layer containing as a main component a resin having a melting
• the multilayer structure of the present invention has high gas barrier properties both before and after folding, and can be used to form a paper container with sufficient strength even in a low-temperature environment, and the occurrence of defects during recycling is suppressed.
• the reason for this is unclear, but the following reasons are presumed.
• the multilayer structure has a structure in which an inorganic vapor deposition 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, and therefore has high gas barrier properties both before and after folding.
• the multilayer structure has a moisture-proof resin layer (E) mainly composed of polyethylene (e).
• a paper container with sufficient strength even in a low-temperature environment can be formed by heat-sealing this moisture-proof resin layer (E) to form a paper container. Furthermore, the occurrence of defects during recycling is suppressed in this multilayer structure because the thickness of the inorganic vapor deposition layer (B) is in a relatively thin range, the barrier resin layer (C) and the moisture-proof resin layer (E) are mainly composed of a specific resin, and the structure does not have a layer containing a resin with a melting point of 200°C or higher as a main component, or a metal layer with an average thickness of 1 ⁇ m or more.
• the term “main component” refers to the component that is contained in the greatest amount by mass.
• the "average thickness” of each layer, etc. refers to the average value of thicknesses measured at any five points.
• “ppm” means the content based on mass (ppm by mass).
• Polyethylene refers to a homopolymer of ethylene, a copolymer of 80 mol % or more ethylene and 20 mol % or less of an ⁇ -olefin monomer, and a copolymer of 90 mol % or more ethylene and less than 10 mol % of a non-olefin monomer whose functional group does not contain atoms other than carbon, oxygen, and hydrogen atoms.
• the term "acid-modified polyethylene” refers to a polymer obtained by modifying polyethylene with an acid.
• the acid-modified polyethylene may be a polymer in which at least one of an acid group and an acid anhydride group is introduced into polyethylene.
• polyethylene resin refers to polyethylene and modified polyethylene (such as acid-modified polyethylene).
• Modified polyethylene refers to a polymer obtained by modifying polyethylene.
• the "surface" of the multilayer structure does not mean to distinguish between the front and back, but refers to the exposed surface. In other words, the multilayer structure has two surfaces. Similarly, the multilayer structure has two outermost layers.
• the paper layer (A) is usually a base layer in the multilayer structure of the present invention.
• the paper layer (A) can be a general paper mainly composed of plant-derived pulp.
• the paper layer (A) may contain, in addition to pulp, a sizing agent, a filler, a paper strength agent, a retention agent, a pH adjuster, a drainage agent, a water resistance agent, a softener, an antistatic agent, an antifoaming agent, a slime control agent, a dye, a pigment, etc.
• Examples of the paper constituting the paper layer (A) include kraft paper, fine paper, medium-quality paper, alkaline paper, paperboard, glassine paper, semi-glassine paper, parchment paper, etc., with kraft paper or paperboard being preferred, and paperboard being more preferred.
• the basis weight (mass per unit area) of the paper layer (A) is not particularly limited, and can be, for example, 50 g/m 2 or more and less than 500 g/m 2 , but is preferably 100 g/m 2 or more and less than 450 g/m 2 , more preferably 200 g/m 2 or more and less than 400 g/m 2 , even more preferably 220 g/m 2 or more and less than 350 g/m 2 , and even more preferably 240 g/m 2 or more and less than 300 g/m 2.
• the basis weight of the paper layer (A) is the lower limit or more, the strength of the obtained paper container in a low-temperature environment can be further increased.
• the basis weight of the paper layer (A) is less than the upper limit, the moldability can be improved.
• the density of the paper layer (A) is, for example, preferably 0.5 g/cm 3 or more and 1.5 g/cm 3 or less, and more preferably 0.7 g/cm 3 or more and 1.3 g/cm 3 or less.
• the paper used in the paper layer (A) can be manufactured by a known method.
• commercially available paper can be used in the paper layer (A).
• the inorganic vapor deposition layer (B) mainly ensures gas barrier properties in the multilayer structure of the present invention.
• the inorganic vapor deposition layer (B) can be formed by vapor deposition of an inorganic material.
• the inorganic vapor deposition layer (B) is formed by vapor deposition of an inorganic material onto the surface of the barrier resin layer (C).
• 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.), carbonitrides (e.g., silicon carbonitride, etc.), etc.
• the inorganic vapor deposition layer (B) is preferably a metal vapor deposition layer or an inorganic oxide vapor deposition layer.
• the inorganic vapor deposition layer (B) is more preferably a metal vapor deposition layer, preferably a metal vapor deposition layer mainly composed of aluminum, or may be an aluminum vapor deposition layer.
• the inorganic vapor deposition layer (B) is preferably an inorganic oxide vapor deposition layer, preferably an inorganic oxide vapor deposition layer mainly composed of alumina (aluminum oxide) or silica (silicon oxide).
• the metal vapor deposition layer mainly composed of aluminum (inorganic vapor deposition layer (B)) oxidation occurs irreversibly, and aluminum oxide may be partially contained.
• the molar ratio of the content of oxygen atoms to the content of aluminum atoms (O mol /Al mol ) is preferably 0.5 or less, more preferably 0.3 or less, and even more preferably 0.1 or less.
• the lower limit of the average thickness of the inorganic vapor deposition layer (B) is 5 nm, preferably 10 nm, more preferably 20 nm, and even more preferably 30 nm. By having the average thickness of the inorganic vapor deposition layer (B) be equal to or greater than the lower limit, it is possible to further improve the gas barrier properties, etc.
• the upper limit of the average thickness of the inorganic vapor deposition layer (B) is 200 nm, preferably 150 nm, more preferably 120 nm, and even more preferably 80 nm. By having the average thickness of the inorganic vapor deposition layer (B) be equal to or less than the upper limit, it is possible to suppress the occurrence of defects, coloration, etc. during recycling. Recycled products (melt-molded products) in which defects, coloration, etc. are suppressed are preferable because of their good appearance, etc.
• the inorganic vapor deposition layer (B) can be provided by a known physical vapor deposition method or chemical vapor deposition method. Specific examples include vacuum vapor deposition, sputtering, ion plating, ion beam mixing, plasma CVD, laser CVD, MO-CVD, and thermal CVD, with physical vapor deposition being preferred and vacuum vapor deposition being more preferred.
• the surface of the layer to be deposited may be plasma-treated.
• the plasma treatment may be performed by a known method, and atmospheric pressure plasma treatment is preferred.
• discharge gases used 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 reducing costs.
• the inorganic vapor deposition layer (B) may consist of a single layer or multiple layers.
• the barrier resin layer (C) contains, as a main component, EVOH (c) having an ethylene unit content of 20 mol% or more and 50 mol% or less and a saponification degree of 90 mol% or more. Since the multilayer structure of the present invention includes such a barrier resin layer (C), it can exhibit high gas barrier properties both in a state before and after folding treatment.
• 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 the ethylene-vinyl ester copolymer 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 versatate, and other vinyl esters of aliphatic carboxylic acids, with vinyl acetate being preferred.
• the lower limit of the ethylene unit content of EVOH (c) is 20 mol%, preferably 24 mol%, and in some cases 28 mol% or 30 mol% is even more preferable.
• the upper limit of the ethylene unit content of EVOH (c) is 50 mol%, preferably 46 mol%, and in some cases 42 mol% or 38 mol% is even more preferable.
• the lower limit of the saponification degree of EVOH (c) is 90 mol%, preferably 95 mol%, more preferably 99 mol%, and even more preferably 99.9 mol%.
• the upper limit of the saponification degree of EVOH (c) may be 100 mol%.
• EVOH (c) may have structural units other than ethylene units, vinyl alcohol units and vinyl ester units, to the extent that the object of the present invention is not impeded.
• a modifying group containing a primary hydroxyl group having a specific structure it may be possible to achieve a high level of both the 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 it is particularly preferable that they are substantially not contained.
• Examples of such other monomers include ⁇ -olefins such as propylene, n-butene, isobutylene, and 1-hexene; acrylic acid and its salts; unsaturated monomers having an acrylic acid ester group; methacrylic acid and its salts; unsaturated monomers having a methacrylic acid ester group; acrylamide, N-methylacrylamide, N-ethylacrylamide, N,N-dimethylacrylamide, diacetoneacrylamide, acrylamidopropanesulfonic acid and its salts, acrylamidopropyldimethylamine and its salts (e.g., quaternary salts); methacrylamide, N-methylmethacrylamide, N-ethylmethacrylamide, methacrylamidopropanesulfonic acid and its salts, methacrylamidopropyldimethylamine and its salts (e.g., quaternary salts); methyl vinyl ether, ethyl vinyl
• 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; vinylidene halides such as vinylidene chloride and vinylidene fluoride; allyl compounds such as allyl acetate, 2,3-diacetoxy-1-allyloxypropane, and allyl chloride; unsaturated dicarboxylic acids and their salts or esters such as maleic acid, itaconic acid, and fumaric acid; vinyl silane compounds such as vinyltrimethoxysilane; isopropenyl acetate, 1,3-diacetoxy-2-methylenepropane, 1,3-dipropionyloxy-2-
• the MFR of EVOH (c) (190°C, 2.16 kg load) is preferably 0.5 g/10 min or more and 12 g/10 min or less, more preferably 0.8 g/10 min or more and 8.0 g/min or less, and even more preferably 1.2 g/10 min or more and 4.0 g/min or less.
• EVOH (c) may be used alone or in combination of two or more types.
• EVOH (c) may contain two or more types of EVOH with different ethylene unit contents. In such a case, it is possible to improve the gas barrier properties after bending and the strength in a low-temperature environment in a more balanced manner.
• the two types of EVOH with different ethylene unit contents may be two types of EVOH with different melting points. For example, when the melting point is measured by DSC, a peak temperature corresponding to each EVOH may be confirmed. In measuring 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 in the second heating.
• the ethylene unit content of EVOH (c1) having the lower ethylene unit content is preferably 20 mol% or more and 40 mol% or less, and more preferably 24 mol% or more and 32 mol% or less.
• the ethylene unit content of EVOH (c2) having the higher ethylene unit content is preferably 32 mol% or more and 50 mol% or less, and more preferably 38 mol% or more and 48 mol% or less.
• the difference in ethylene unit content between EVOH (c2) and EVOH (c1) (c2-c1) i.e., the value obtained by subtracting the ethylene unit content of EVOH (c1) from the ethylene unit content of EVOH (c2), is preferably from 4 mol% to 40 mol%, more preferably from 8 mol% to 30 mol%, even more preferably from 12 mol% to 25 mol%, and even more preferably from 15 mol% to 20 mol%.
• the mass ratio (c1/c2) of EVOH (c1) to EVOH (c2) i.e., the mass ratio of the content of EVOH (c1) to the content of EVOH (c2), 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.
• the lower limit of the content of EVOH (c) in the barrier resin layer (C) is preferably 70 mass%, more preferably 80 mass%, and even more preferably 90 mass%, and may be 95 mass%, 99 mass%, or 99.9 mass%, from the viewpoint of gas barrier properties, etc.
• the upper limit of the content of EVOH (c) in the barrier resin layer (C) may be 100 mass%, or may be 99.99 mass%.
• 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 content of the polyvalent metal ions in the barrier resin layer (C) is preferably 10 ppm, more preferably 30 ppm, and even more preferably 50 ppm. In some cases, 80 ppm may be even more preferable when emphasis is placed on suppressing defects in the recycled resin.
• the barrier resin layer (C) contains the polyvalent metal ions at or above the lower limit, the occurrence of defects during recycling is further suppressed.
• the upper limit of the content of the polyvalent metal ions in the barrier resin layer (C) may be, for example, 300 ppm, but is preferably 200 ppm, more preferably 150 ppm, and even more preferably 120 ppm. In some cases, 80 ppm may be even more preferable when emphasis is placed on suppressing coloring of the recycled resin.
• the content of the polyvalent metal ions in the barrier resin layer (C) is equal to or less than the upper limit, the occurrence of coloring during recycling is suppressed.
• the polyvalent metal ions preferably contain magnesium ions, and more preferably are magnesium ions. In such cases, the occurrence of defects during recycling is further suppressed.
• the polyvalent metal ion is preferably present in the barrier resin layer (C) as a cation constituting a salt, and more preferably present in the barrier resin layer (C) as a cation constituting a carboxylate.
• the polyvalent metal ion and the anion may be bonded or free.
• the carboxylate 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 is present in the form of such a higher fatty acid salt, the occurrence of coloring during recycling is further suppressed.
• carboxylic acids having 12 or more carbon atoms include lauric acid, lauric acid, tridecylic acid, myristic acid, pentadecylic acid, palmitic acid, heptadecylic 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 of the carboxylic acid may be 12 or more and 30 or less, 14 or more and 26 or less, or 16 or more and 22 or less.
• the polyvalent metal ions may be present in the barrier resin layer (C) as cations constituting fatty acid salts having 11 or less carbon atoms (acetates, propionates, etc.), salts other than fatty acid salts (nitrates, sulfates, etc.), etc.
• a part or all of the polyvalent metal ions may be present in a state coordinated to, for example, hydroxyl groups of EVOH (c).
• the barrier resin layer (C) may contain optional components other than EVOH (c) and the polyvalent metal ions or salts containing the polyvalent metal ions, such as boron compounds, carboxylic acids, phosphorus compounds, metal ions other than the polyvalent metal ions, antioxidants, UV absorbers, plasticizers, antistatic agents, lubricants, colorants, fillers, heat stabilizers, resins other than EVOH (c), etc.
• the barrier resin layer (C) may contain two or more of these optional components.
• 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 above boric acids, borate salts such as borax; and boron hydrides.
• the content of the boron compound in the barrier resin layer (C) is preferably 10 ppm or more and 1,000 ppm or less, and more preferably 50 ppm or more and 400 ppm or less. By setting the content of the boron compound within the above range, the melt moldability, appearance, etc. are improved.
• the content of the boron compound is the content converted to elemental boron.
• Carboxylic acids include formic acid, acetic acid, propionic acid, butyric acid, lactic acid, and salts thereof. Carboxylic acids are preferably carboxylic acids having 4 or less carbon atoms or saturated carboxylic acids, and more preferably acetic acid. Carboxylic acids may also include carboxylates containing the above-mentioned polyvalent metal ions.
• Examples of phosphorus compounds include phosphates such as phosphoric acid and phosphorous acid.
• the phosphates may be in the form of primary phosphates, secondary phosphates, or tertiary phosphates.
• the cationic species of the phosphates is not particularly limited, but is preferably an alkali metal salt or an alkaline earth metal salt, and among these, sodium dihydrogen phosphate, potassium dihydrogen phosphate, disodium hydrogen phosphate, or dipotassium hydrogen phosphate is more preferred.
• the content of the phosphorus compound in the barrier resin layer (C) is preferably 1 ppm or more and 200 ppm or less, and more preferably 10 ppm or more and 100 ppm or less. By setting the content of the phosphorus compound within the above range, the thermal stability is improved and defects and coloring during recycling are suppressed.
• the content of the phosphorus compound is the content converted into phosphate radical.
• metal ions other than the polyvalent metal ions include monovalent metal ions and polyvalent metal ions other than the polyvalent metal ions, with monovalent metal ions being preferred.
• monovalent metal ion an alkali metal ion is preferred.
• alkali metal ions include lithium ions, sodium ions, potassium ions, etc., and sodium ions or potassium ions are preferred from the viewpoint of industrial availability.
• 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 is preferred.
• the content of alkali metal ions in the barrier resin layer (C) is preferably 10 ppm or more and 1,000 ppm or less, and more preferably 100 ppm or more and 400 ppm or less.
• antioxidants examples 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.
• ultraviolet absorbers examples include ethylene-2-cyano-3,3'-diphenylacrylate, 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.
• Plasticizers include, for example, dimethyl phthalate, diethyl phthalate, dioctyl phthalate, wax, liquid paraffin, and phosphate esters.
• antistatic agents examples include pentaerythritol monostearate, sorbitan monopalmitate, sulfated polyolefins, polyethylene oxide, and polyethylene glycol (trade name: Carbowax).
• lubricants examples include ethylene bisstearamide and butyl stearate.
• Colorants include, for example, carbon black, phthalocyanine, quinacridone, indoline, azo pigments, red iron oxide, etc.
• Fillers include, for example, glass fiber, wollastonite, calcium silicate, talc, montmorillonite, etc.
• Heat stabilizers include, for example, hindered phenol compounds and hindered amine compounds.
• resins besides EVOH (c) include, for example, polyamides, polyolefins, etc.
• the barrier resin layer (C) may be a non-stretched layer or a stretched layer. When the barrier resin layer (C) is a stretched layer, it can exhibit good gas barrier properties even when the barrier resin layer (C) is relatively thin.
• the lower limit of the average thickness of the barrier resin layer (C) is preferably 0.1 ⁇ m, more preferably 0.2 ⁇ m, even more preferably 0.4 ⁇ m, even more preferably 0.5 ⁇ m, 0.6 ⁇ m, 0.8 ⁇ m or 1 ⁇ m, and may be 2 ⁇ m.
• the upper limit of the average thickness of the barrier resin layer (C) is preferably 30 ⁇ m, more preferably 20 ⁇ m, even more preferably 15 ⁇ m, even more preferably 10 ⁇ m or 5 ⁇ m, and may be 3 ⁇ m. By having the average thickness of the barrier resin layer (C) be equal to or less than the upper limit, it is possible to suppress the occurrence of coloration during recycling, etc.
• the barrier resin layer (C) may consist of a single layer or multiple layers.
• the adhesive resin layer (D) contains an adhesive resin (d) as a main component, and adheres the barrier resin layer (C) and the moisture-proof resin layer (E) to each other.
• the adhesive resin (d) is not particularly limited as long as it is a resin having adhesive properties, and examples thereof include acid-modified polyolefins (carboxylic acid-modified polyolefins, sulfonic acid-modified polyolefins, etc.), epoxy-modified polyolefins, etc.
• 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 an acid-modified polyethylene.
• the adhesive resin (d) is also preferably a carboxylic acid-modified polyolefin, and more preferably a carboxylic acid-modified polyethylene.
• Carboxylic acid-modified polyolefins may be polyolefins having a carboxy group or an anhydride group thereof.
• Carboxylic acid-modified polyolefins (polyolefins having a carboxy group or an anhydride group thereof) can be obtained, for example, by chemically bonding an ethylenically unsaturated carboxylic acid or an anhydride thereof to an unmodified polyolefin by an addition reaction, a grafting reaction, or the like.
• the unmodified polyolefin used in the production of carboxylic acid modified polyolefins is preferably polyethylene.
• 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. Specific examples include maleic acid, fumaric acid, itaconic acid, maleic anhydride, itaconic anhydride, maleic acid monomethyl ester, maleic acid monoethyl ester, maleic acid diethyl ester, and fumaric acid monomethyl ester. Among these, dicarboxylic acid anhydrides such as maleic anhydride and itaconic anhydride are preferred, and maleic anhydride is more preferred.
• the adhesive resin (d) is also preferably a maleic anhydride-modified polyolefin, and more preferably a maleic anhydride-modified polyethylene.
• Carboxylic acid-modified polyolefins are obtained by introducing an ethylenically unsaturated carboxylic acid or its anhydride into an unmodified polyolefin through an addition reaction or a 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 to the unmodified polyolefin or the graft amount (degree of modification) is preferably 0.01% by mass, more preferably 0.02% by mass, based on the unmodified polyolefin.
• the upper limit of the amount of addition or graft amount (degree of modification) is preferably 15% by mass, more preferably 10% by mass, based on the unmodified polyolefin.
• the acid value of the acid-modified polyolefin is preferably 0.3 mgKOH/g or more and 5.0 mgKOH/g or less, and more preferably 1.0 mgKOH/g or more and 3.0 mgKOH/g or less.
• the MFR (190°C, 2.16 kg load) of the adhesive resin (d) is preferably 0.5 g/10 min or more and 12 g/10 min or less, and more preferably 1.0 g/10 min or more and 8.0 g/min or less.
• the adhesive resin (d) may be used alone or in combination of two or more types.
• the content of adhesive resin (d) in 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 contain components other than adhesive resin (d), such as antioxidants, ultraviolet absorbers, plasticizers, antistatic agents, lubricants, colorants, fillers, heat stabilizers, and other resins other than adhesive resin (d).
• the adhesive resin layer (D) may be a non-stretched layer or a stretched layer.
• the lower limit of the average thickness of the adhesive resin layer (D) is preferably 0.1 ⁇ m, more preferably 0.5 ⁇ m, even more preferably 1 ⁇ m, and may be 2 ⁇ m. By having the average thickness of the adhesive resin layer (D) be equal to or greater than the lower limit, sufficient adhesion can be exhibited. In addition, defects and coloring during recycling can be further suppressed.
• the upper limit of the average thickness of the adhesive resin layer (D) is preferably 20 ⁇ m, more preferably 10 ⁇ m, even more preferably 5 ⁇ m, and may be 3 ⁇ m. By having the average thickness of the adhesive resin layer (D) be equal to or less than the upper limit, defects and coloring during recycling can be further suppressed.
• the adhesive resin layer (D) may consist of a single layer or multiple layers.
• the moisture-proof resin layer (E) contains polyethylene (e) as a main component.
• polyethylene (e) as a main component of the moisture-proof resin layer (E)
• the multilayer structure of the present invention can exhibit sufficient moisture-proofing.
• the multilayer structure of the present invention can be molded into a paper container having sufficient strength even in a low-temperature environment, and the occurrence of defects during recycling is also suppressed.
• the moisture-proof resin layer (E) may be a heat-sealing layer for bonding the moisture-proof resin layers (E) to each other or the moisture-proof resin layer (E) to another layer by heat sealing. From the viewpoint of further increasing the strength of the obtained paper container in a low-temperature environment, the moisture-proof resin layer (E) may be the outermost layer in the multilayer structure.
• the type of polyethylene (e) is not particularly limited, and examples thereof include high-density polyethylene, low-density polyethylene, and linear low-density polyethylene. Of these, linear low-density polyethylene, low-density polyethylene, or a mixture thereof is preferred.
• Linear low-density polyethylene is a resin obtained by polymerizing ethylene with an ⁇ -olefin having 3 or more carbon atoms. Examples of ⁇ -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.
• linear low-density polyethylene is preferably linear low-density polyethylene obtained by polymerizing ethylene with an ⁇ -olefin having 6 or more carbon atoms, and more preferably linear low-density polyethylene obtained by polymerizing ethylene with an ⁇ -olefin having 8 or more carbon atoms.
• various mechanical strengths such as puncture strength and tensile strength may be particularly improved.
• the linear low-density polyethylene polymerized using a metallocene catalyst is produced by copolymerizing ethylene and an ⁇ -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 necessary.
• the linear low-density polyethylene polymerized using a metallocene catalyst has excellent melt moldability, and the resulting multilayer film has an excellent balance of heat resistance, flexibility, and mechanical strength. By using such polyethylene, it is possible to further increase the strength of the molded paper container in a low-temperature environment.
• One or more types of polyethylene (e) can be used.
• the upper limit of the density of the polyethylene (e) can be, for example, 0.96 g/cm 3 , preferably 0.940 g/cm 3 , and more preferably 0.930 g/cm 3.
• the lower limit of the density of the polyethylene (e) is preferably 0.880 g/cm 3 , more preferably 0.890 g/cm 3 , and may be 0.900 g/cm 3 or 0.910 g/cm 3.
• the MFR of the polyethylene (e) (190°C, 2.16 kg load) is preferably 0.4 g/10 min or more and 4.0 g/10 min or less, and more preferably 0.8 g/10 min or more and 2.0 g/min or less.
• the content of polyethylene (e) in the moisture-proof resin layer (E) 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 moisture-proof resin layer (E) may contain components other than polyethylene (e), such as antioxidants, ultraviolet absorbers, plasticizers, antistatic agents, lubricants, colorants, fillers, heat stabilizers, and other resins other than polyethylene (e).
• the moisture-proof resin layer (E) may be a non-stretched layer or a stretched layer.
• the lower limit of the average thickness of the moisture-proof resin layer (E) is preferably 1 ⁇ m, more preferably 5 ⁇ m, even more preferably 10 ⁇ m, even more preferably 20 ⁇ m, and may be 30 ⁇ m, 40 ⁇ m, or 45 ⁇ m.
• the upper limit of the average thickness of the moisture-proof resin layer (E) is preferably 200 ⁇ m, more preferably 100 ⁇ m, and may be 50 ⁇ m.
• the moisture-proof resin layer (E) may consist of a single layer or multiple layers.
• the multilayer structure of the present invention preferably further has a thermoplastic resin layer (X) interposed between the paper layer (A) and the inorganic vapor deposition layer (B) or the moisture-proof resin layer (E).
• the multilayer structure of the present invention preferably has a layer structure in which the paper layer (A) and the inorganic vapor deposition layer (B) or the moisture-proof resin layer (E) are laminated via the thermoplastic resin layer (X).
• the paper layer (A) is laminated via the thermoplastic resin layer (X) on one side of a laminate (composite film) of the inorganic vapor deposition layer (B), the barrier resin layer (C), the adhesive resin layer (D) and the moisture-proof resin layer (E).
• thermoplastic resin layer (X) By the multilayer structure having such a thermoplastic resin layer (X), it is possible to increase the adhesion between the paper layer (A) and the inorganic vapor deposition layer (B) or the moisture-proof resin layer (E).
• the thermoplastic resin layer (X) defects and coloring during recycling can be further suppressed.
• the thermoplastic resin layer (X) is mainly composed of a thermoplastic resin.
• the thermoplastic resin there are no particular limitations on the thermoplastic resin as long as it is a thermoplastic resin with a melting point of less than 200°C, and examples of the thermoplastic resin include polyolefin, polystyrene, polycarbonate, acrylic resin, and the adhesive resins described above (such as acid-modified polyolefin). Among these, polyolefin or acid-modified polyolefin is preferred, polyolefin is more preferred, and polyethylene is even more preferred.
• the thermoplastic resin layer (X) mainly composed of such a thermoplastic resin, it is possible to suppress the occurrence of coloring during recycling, etc.
• the content of the thermoplastic resin in the thermoplastic resin layer (X) 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 thermoplastic resin layer (X) may 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.
• the lower limit of the average thickness of the thermoplastic resin layer (X) is preferably 1 ⁇ m, more preferably 3 ⁇ m, even more preferably 5 ⁇ m, and even more preferably 10 ⁇ m.
• the upper limit of the average thickness of the thermoplastic resin layer (X) is preferably 100 ⁇ m, more preferably 50 ⁇ m, and may be 30 ⁇ m.
• the thermoplastic resin layer (X) is preferably an extruded resin layer. That is, the paper layer (A) and the inorganic vapor deposition layer (B) (or a coextruded film having an inorganic vapor deposition layer (B) described later on one side) or the moisture-proof resin layer (E) (or a coextruded film having an inorganic vapor deposition layer (E) described later on one side) are preferably laminated by sandwich lamination.
• the paper layer (A) and the inorganic vapor deposition layer (B) (or a coextruded film having an inorganic vapor deposition layer (B) described later on one side) or the moisture-proof resin layer (E) (or a coextruded film having an inorganic vapor deposition layer (E) described later on one side) may be laminated by other methods, such as dry lamination.
• the layer interposed between the paper layer (A) and the inorganic vapor deposition layer (B) or the moisture-proof resin layer (E) may be an adhesive layer other than the thermoplastic resin layer (X).
• the laminate of the barrier resin layer (C), the adhesive resin layer (D) and the moisture-proof resin layer (E) is preferably a coextruded film. That is, the barrier resin layer (C), the adhesive resin layer (D) and the moisture-proof resin layer (E) are preferably formed by coextrusion. This makes it possible to achieve a high level of balance between film properties such as barrier properties and flexibility, and processability and economic efficiency. Furthermore, it is preferable that an inorganic vapor deposition layer (B) is provided on the surface of the barrier resin layer (C) side of the coextruded film.
• the inorganic vapor deposition layer (B) may be provided by vapor deposition on the surface of the barrier resin layer (C) side of the coextruded film.
• the lower limit of the average thickness of the coextruded film is preferably 8 ⁇ m, more preferably 15 ⁇ m, and even more preferably 25 ⁇ m. By having the average thickness of the coextruded film be equal to or greater than the lower limit, the gas barrier properties and strength of the resulting paper container in a low-temperature environment can be improved.
• the upper limit of the average thickness of the coextruded film is preferably 120 ⁇ m, more preferably 80 ⁇ m, and even more preferably 60 ⁇ m. By having the average thickness of the coextruded film be equal to or less than the upper limit, it is possible to reduce the thickness of the multilayer structure.
• the average thickness of the coextruded film is equal to the sum of the average thicknesses of all layers of the coextruded film.
• the average thickness of the barrier resin layer (C) of the coextruded film is preferably 0.2 ⁇ m or more and less than 30 ⁇ m. It is also preferable that the ratio of the average thickness of the barrier resin layer (C) to the average thickness of the coextruded film is less than 25%.
• the average thickness of the barrier resin layer (C) is more preferably 0.4 ⁇ m or more and less than 15 ⁇ m, even more preferably 0.6 ⁇ m or more and less than 10 ⁇ m, and even more preferably 0.8 ⁇ m or more and less than 5 ⁇ m.
• the ratio of the average thickness of the barrier resin layer (C) to the average thickness of the coextruded film is more preferably less than 20%, and even more preferably less than 15%.
• the coextruded film may be a non-stretched film that is not substantially stretched, or a uniaxially or biaxially stretched film. If it is a non-stretched film, the strength of the resulting paper container in a low-temperature environment tends to be increased. If it is a stretched film, the gas barrier properties tend to be improved.
• the coextruded film is preferably stretched, for example, at least uniaxially by 3 times to less than 12 times, and more preferably stretched at least uniaxially by 4 times to less than 10 times.
• the coextruded film is also preferably stretched in each of two axial directions by 3 times to less than 12 times, and more preferably stretched in each of two axial directions by 3.5 times to less than 10 times.
• the multilayer structure of the present invention preferably further comprises a moisture-proof resin layer (F) other than the moisture-proof resin layer (E).
• the moisture-proof resin layer (F) contains polyethylene (f) as a main component.
• the moisture-proof resin layer (F) may be a heat-sealing layer for bonding the moisture-proof resin layers (F) to each other or to the moisture-proof resin layer (F) and another layer by heat sealing.
• the moisture-proof resin layer (F) may be the outermost layer in the multilayer structure.
• the moisture-proof resin layer (F) mainly composed of polyethylene (f) defects and coloring during recycling are suppressed.
• the moisture-proof resin layer provided on the side opposite to the side on which the inorganic vapor deposition layer (B) and the like of the paper layer (A) are provided (hereinafter also referred to as the "exposed surface side") is the moisture-proof resin layer (F).
• the moisture-proof resin layer different from the moisture-proof resin layer (E) constituting the coextruded film is a moisture-proof resin layer (F).
• the coextruded film comprises a plurality of moisture-proof resin layers
• all of these moisture-proof resin layers are moisture-proof resin layers (E).
• the multilayer structure does not have the coextruded film and has a plurality of moisture-proof resin layers (excluding the case where the moisture-proof resin layer is on the exposed surface side of the paper layer (A))
• all of these moisture-proof resin layers are moisture-proof resin layers (E).
• the type, physical properties, and specific and preferred forms of the polyethylene (f) are the same as those of the polyethylene (e) except for the MFR.
• the density of the polyethylene (f) is preferably 0.880 g/cm 3 or more and 0.940 g/cm 3 or less.
• the polyethylene (f) is preferably a linear low-density polyethylene, a low-density polyethylene, or a mixture thereof.
• the MFR (190° C., 2.16 kg load) of the polyethylene (f) is preferably 0.4 g/10 min or more and 30.0 g/10 min or less, more preferably 0.8 g/10 min or more and 20.0 g/min or less, and even more preferably 1.0 g/10 min or more and 10.0 g/min or less.
• the moisture-proof resin layer (F) is preferably a non-stretched layer.
• the moisture-proof resin layer (F) may be a stretched layer.
• 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 laminated directly onto the coextruded film.
• 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 coextruded film.
• 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.).
• another layer e.g., an adhesive resin layer, another adhesive layer, etc.
• the moisture-proof resin layer (F) can be laminated by dry lamination, sandwich lamination, etc. between the co-extruded film and a single-layer film of the moisture-proof resin layer (F).
• the moisture-proof resin layer (F) may be laminated directly or via another layer on the surface of the paper layer (A) opposite the inorganic vapor deposition layer (B).
• 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 a multilayer structure including the paper layer (A) with a monolayer film of the moisture-proof resin layer (F), sandwich lamination, etc.
• 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).
• Examples of other layers that the multilayer structure of the present invention may have include other thermoplastic resin layers, adhesive layers, printed layers, etc.
• the multilayer structure does not have a layer containing a resin having a melting point of 200° C. or more as a main component and a metal layer having an average thickness of 1 ⁇ m or more. When the multilayer structure contains a layer containing a resin having a melting point of 200° C.
• a main component e.g., a layer containing polyethylene terephthalate as a main component
• a metal layer having an average thickness of 1 ⁇ m or more e.g., a metal foil layer having an average thickness of 1 ⁇ m or more
• the multilayer structure of the present invention does not have an adhesive layer made of a curing adhesive. By not having such an adhesive layer, defects during recycling are further suppressed.
• the multilayer structure of the present invention 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 deposition 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.
• the multilayer structure preferably has the paper layer (A), the inorganic vapor deposition layer (B), the barrier resin layer (C), the adhesive resin layer (D), and the moisture-proof resin layer (E) in this order, particularly from the viewpoint of increasing the strength in a low-temperature environment.
• the multilayer structure may have the paper layer (A), the moisture-proof resin layer (E), the adhesive resin layer (D), the barrier resin layer (C), and the inorganic vapor deposition layer (B) in this order.
• the paper layer (A) and the inorganic vapor deposition layer (B) or the moisture-proof resin layer (E) may be directly laminated, but are usually laminated via another layer.
• the layer interposed between the paper layer (A) and the inorganic vapor deposition layer (B) or the moisture-proof resin layer (E) may be a thermoplastic resin layer (X) or another adhesive layer.
• the multilayer structure may further have a moisture-proof resin layer (F).
• 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 the paper layer (A). However, when a paper container is formed from the multilayer structure, it is preferable that the surface on which the paper layer (A) is exposed becomes the outer surface. When the multilayer structure has the paper layer (A) on its surface, it becomes easier to detect the paper, specifically, to detect the paper by measuring the infrared spectrum using, for example, a total reflection measurement method. Therefore, in such a multilayer structure, the paper recycling rate can be increased.
• the multilayer structure of the present invention has a moisture-proof resin layer (E) or a moisture-proof resin layer (F) on one surface. That is, in the multilayer structure, it is preferable that one of the outermost layers is the moisture-proof resin layer (E) or the moisture-proof resin layer (F).
• the surface on which the moisture-proof resin layer (E) or the moisture-proof resin layer (F) is exposed becomes the inner surface.
• these layers are bonded by heat sealing, and a paper container having higher strength in a low-temperature environment can be formed.
• the multilayer structure has a moisture-proof resin layer (E) or a moisture-proof resin layer (F) on the surface, it becomes easy to detect polyethylene, specifically, to detect polyethylene by measuring an infrared spectrum using, for example, a total reflection measurement method. Therefore, in such a multilayer structure, the recycling rate of polyethylene can be increased.
• 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.
• a paper container is formed from the multilayer structure, it is preferable that the surface on which the paper layer (A) is exposed becomes the outer surface, and the surface on which the moisture-proof resin layer (E) or the moisture-proof resin layer (F) is exposed becomes the inner surface.
• the layer configuration of the multilayer structure of the present invention is not limited to the following configuration.
• “/” indicates that the layers are directly laminated.
• Ad indicates an optional 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)).
• 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/F (15) A/Ad/E/D/C/B/F (16) A/
• the lower limit of the total average thickness ratio of the layers mainly composed of polyethylene resin in the parts other than the paper layer (A) of the multilayer structure of the present invention is preferably 0.75, more preferably 0.80, even more preferably 0.85, and even more preferably 0.90.
• the upper limit of the total average thickness ratio of the layers mainly composed of polyethylene resin in the parts other than the paper layer (A) is preferably 0.995, more preferably 0.99, and may be 0.98.
• 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 a polyethylene resin (polyethylene or modified polyethylene).
• the lower limit of the total average thickness ratio of layers mainly composed of resin having ethylene units in the parts other than the paper layer (A) of the multilayer structure of the present invention is preferably 0.95, more preferably 0.98, and even more preferably 0.99.
• the upper limit of the total average thickness ratio of layers mainly composed of resin having ethylene units in the parts other than the paper layer (A) may be, for example, 0.9999.
• layers mainly composed of resin having ethylene units include the above-mentioned layer mainly composed of polyethylene-based resin, as well as the barrier resin layer (C).
• the lower limit of the total average thickness ratio of layers mainly composed of a thermoplastic resin having a melting point of less than 200°C in the parts other than the paper layer (A) of the multilayer structure of the present invention is preferably 0.95, more preferably 0.98, and even more preferably 0.99.
• the upper limit of the total average thickness ratio of layers mainly composed of a thermoplastic resin having a melting point of less than 200°C in the parts other than the paper layer (A) may be, for example, 0.9999.
• the lower limit of the average thickness of the multilayer structure of the present invention is preferably 150 ⁇ m, more preferably 200 ⁇ m, even more preferably 250 ⁇ m, and even more preferably 300 ⁇ m.
• the upper limit of the average thickness of the multilayer structure is preferably 1,000 ⁇ m, and may be 700 ⁇ m or 500 ⁇ m.
• the oxygen transmission rate measured by the method described in JIS K 7126-2:2006 under conditions of 20°C and 65% RH is preferably less than 0.5 cc/( m2 ⁇ day ⁇ atm), more preferably less than 0.1 cc/( m2 ⁇ day ⁇ atm).
• the upper limit of this oxygen transmission rate may be 0.001 cc/( m2 ⁇ day ⁇ atm) or 0.01 cc/( m2 ⁇ day ⁇ atm).
• the sheet is folded in four so that the paper layer (A) is on the outside relative to the moisture-proof resin layer (E), and then a load of 5 kg is applied from above and left to stand for 1 minute to perform folding treatment.
• the oxygen transmission rate measured under 20°C and 65% RH conditions by the method described in JIS K 7126-2:2006 is preferably less than 1.0 cc/( m2 ⁇ day ⁇ atm), more preferably less than 0.2 cc/( m2 ⁇ day ⁇ atm). Since the oxygen transmission rate after folding treatment is less than the upper limit, the sheet can be particularly suitably used as a molding material for paper containers in which folding treatment is usually performed.
• the lower limit of the oxygen transmission rate after folding treatment may be 0.002 cc/( m2 ⁇ day ⁇ atm) or 0.02 cc/( m2 ⁇ day ⁇ atm).
• the multilayer structure of the present invention can be pulverized for reuse, separated into the paper layer (A) and the portion other than the paper layer (A), and the portion other than the paper layer (A) can be used as a melt molding material.
• a melt molded product (recycled product) with fewer defects can be obtained.
• the portion of the multilayer structure other than the paper layer (A) can be mixed with other melt molding materials (other recycled resins, unused resins, etc.).
• the separated paper layer (A) can also be reused.
• the method for producing the multilayer structure of the present invention is not particularly limited.
• a coextruded film of a barrier resin layer (C), an adhesive resin layer (D), and a moisture-proof resin layer (E) is produced by coextrusion.
• An inorganic vapor deposition layer (B) is provided on the barrier resin layer (C) side of the coextruded film to produce a composite film.
• a multilayer structure is obtained by laminating the paper layer (A), which is the paper layer, and the composite film by known means such as sandwich lamination or dry lamination so that the paper layer (A) faces the inorganic vapor deposition layer (B) or the moisture-proof resin layer (E).
• 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.
• a composite film may be produced by providing an inorganic vapor deposition 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).
• a two-layer film of an inorganic vapor deposition layer (B) and a barrier resin layer (C) may be laminated with a paper layer, and then an adhesive resin layer (D) and a moisture-proof resin layer (E) may be laminated.
• the multilayer structure of the present invention is suitable for use as a molding material for paper containers.
• the use of the paper container is not particularly limited, and it may be a container for storing solids such as food, but it is preferable that it is a container for storing liquids.
• the multilayer structure may be used for purposes other than as a molding material for paper containers.
• the paper container for liquids of the present invention is a paper container formed from the multilayer structure of the present invention.
• the paper container has high gas barrier properties even in the folded portion, has sufficient strength even in a low-temperature environment, and suppresses the occurrence of defects during recycling.
• the paper container for liquids is suitably used as a container for storing beverages such as milk and juice, liquid foods such as soup, alcoholic beverages such as sake and shochu, and various liquids other than food.
• the paper container for liquids 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 parts by heat sealing or the like.
• the paper layer (A) is located on the outer surface.
• the moisture-proof resin layer (E) or the moisture-proof resin layer (F) is located on the inner surface.
• the shape of the paper container for liquid of the present invention is not limited to a box shape, and may be other shapes (e.g., bag shape, etc.).
• the paper container for liquid may be bonded by a method other than heat sealing, and may have parts bonded by heat sealing and parts bonded by other methods.
• the paper container for liquid may further have a member other than the multilayer structure of the present invention.
• Example 1 (1) Preparation of EVOH (c)-containing resin composition for barrier resin layer (C) EVOH (c-1) (ethylene unit content 32 mol%, saponification degree 99.99 mol%, MFR (190°C, 2.16 kg load) 1.6 g/10 min, sodium acetate 220 ppm calculated as sodium ion, phosphate ion 30 ppm calculated as phosphate radical, boric acid 150 ppm calculated as boron element, no polyvalent metal ion) and magnesium stearate (Mg-St) were melt-kneaded so that the magnesium ion content in the resulting resin composition was 50 ppm, to obtain resin composition pellets for the barrier resin layer (C).
• the resin temperature was set to 220°C.
• Adhesive resin (d-1) was prepared using maleic anhydride modified polyethylene "ADMER (trademark) NF518" manufactured by Mitsui Chemicals, Inc. (MFR (190°C, 2.16 kg load) 3.1 g/10 min, density 0.91 g/cm 3 , acid value 1.8 mgKOH/g). Pellets of this adhesive resin (d-1) were used as they were as the resin composition pellets for the adhesive resin layer (D).
• Extrusion temperature of moisture-proof resin layer (E): feeding section/compression section/metering section/adapter 175/220/220/220° C. Die temperature: 220°C Chill roll temperature: 80°C
• thermoplastic resin layer (X) thermoplastic resin layer having an average thickness of 20 ⁇ m
• 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 specified MFR at 190°C. Therefore, it is clear that the melting points of these resins are less than 200°C. The same applies to the other examples described below.
• Oxygen transmission rate (OTR) of the multilayer structure was measured in accordance with the method described in JIS K 7126-2 (isobaric method; 2006) with the paper layer as the oxygen supply side and the composite film as the carrier gas side.
• the oxygen transmission rate (unit: cc/(m2 ⁇ day ⁇ atm)) was measured under the conditions of a temperature of 20°C, a humidity of 65% RH on the oxygen supply side, a humidity of 65% RH on the carrier gas side, an oxygen pressure of 1 atm, and a carrier gas pressure of 1 atm, and the evaluation was made according to the following criteria. Nitrogen gas containing 2% by volume of hydrogen gas was used as the carrier gas. The results are shown in Table 2. In the cases of A to D, it was determined that the gas barrier property was high in a state in which folding treatment was not performed.
• Oxygen transmission rate after folding treatment of multilayer structure OTR after folding
• the multilayer structure obtained in (6) was cut into a 10 cm square, folded in four so that the paper layer (A) was on the outside of the moisture-proof resin layer (E), and in that state, a load of 5 kg was applied from above and left to stand for 1 minute, thereby performing a folding treatment.
• the load of 2 kg was removed, and the multilayer structure was opened with the folds, and the oxygen transmission rate was measured in accordance with 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.
• the oxygen transmission rate (unit: cc/( m2 ⁇ day ⁇ atm)) was measured under the conditions of a temperature of 20°C, a humidity of 65% RH on the oxygen supply side, a humidity of 65% RH on the carrier gas side, an oxygen pressure of 1 atm, and a carrier gas pressure of 1 atm, and the evaluation was performed according to the following criteria. Nitrogen gas containing 2% by volume of hydrogen gas was used as the carrier gas. The results are shown in Table 2. In the cases of A to D, it was determined that the gas barrier properties were high after the folding treatment.
• LDPE low-density polyethylene resin
• Novatec (trademark) LD LJ400 MFR (190°C, 2.16 kg load) 1.5 g/10 min, density 0.921 g/cm 3 ) manufactured by Japan Polyethylene Co., Ltd. in a mass ratio (collected material/low-density polyethylene resin) of 40/60, and a monolayer film was formed under the extrusion conditions shown below to obtain a monolayer film having a thickness of 50 ⁇ m.
• a monolayer film having a thickness of 50 ⁇ m was obtained similarly using only the low-density polyethylene resin.
• a T-die with a width of 300 mm 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: feeding section/compression section/metering section/adapter 175/220/220/220°C Die temperature: 220°C Chill roll temperature: 80°C
• the obtained monolayer films were visually evaluated for coloration and defects, and judged according to the following criteria. The results are shown in Table 2.
• Criterion A The degree of change in hue was small compared to the control.
• B Slight coloring was observed compared to the control.
• C Moderate coloring was observed compared to the control.
• D Significant coloring was observed compared to the control.
• E Significant coloring was observed compared to the control, and unevenness was also observed.
• Criterion A The amount of lumps was almost the same compared to the control.
• B The amount of small lumps was slightly more than the control.
• C The amount of small lumps was more than the control.
• D The amount of large lumps was more than the control.
• E The amount of large lumps was significantly more than the control.
• Example 2 Resin composition pellets, coextruded films, composite films and multilayer structures were produced in the same manner as in Example 1, except that EVOH (c-2) (ethylene unit content 27 mol%, saponification degree 99.99 mol%, MFR (210°C, 2.16 kg load) 4.0 g/10 min, sodium acetate 220 ppm calculated as sodium ions, phosphate ions 30 ppm calculated as phosphate radicals, boric acid 150 ppm calculated as boron element, no polyvalent metal ions) was used instead of EVOH (c-1), and various measurements and evaluations were performed. The results are shown in Table 2.
• EVOH (c-2) ethylene unit content 27 mol%, saponification degree 99.99 mol%, MFR (210°C, 2.16 kg load) 4.0 g/10 min
• Example 3 Resin composition pellets, a coextruded film, a composite film and a multilayer structure were prepared in the same manner as in Example 1, except that EVOH (c-3) (ethylene unit content 44 mol%, saponification degree 99.99 mol%, MFR (190°C, 2.16 kg load) 5.7 g/10 min, containing 220 ppm of sodium acetate calculated as sodium ions, 30 ppm of phosphate ions calculated as phosphate radicals, and containing no polyvalent metal ions) was used instead of EVOH (c-1), and various measurements and evaluations were carried out. The results are shown in Table 2.
• EVOH (c-3) ethylene unit content 44 mol%, saponification degree 99.99 mol%, MFR (190°C, 2.16 kg load) 5.7 g/10 min, containing 220 ppm of sodium acetate calculated as sodium ions, 30 ppm of phosphate ions calculated as phosphate radicals, and containing no polyvalent metal ions
• Example 4 Except for using a mixture (dry blend) of EVOH (c-2) and EVOH (c-3) in a mass ratio of 75/25 instead of EVOH (c-1), resin composition pellets, coextruded films, composite films and multilayer structures were produced in the same manner as in Example 1, and various measurements and evaluations were carried out. The results are shown in Table 2.
• Example 5 Except for changing the average thickness of the aluminum metal vapor deposition layer to 100 nm, resin composition pellets, coextruded films, composite films, and multilayer structures were produced in the same manner as in Example 1, and various measurements and evaluations were carried out. The results are shown in Table 2.
• Example 6 Except for changing the aluminum metal deposition layer to an alumina (AlOx) deposition layer, resin composition pellets, coextruded films, composite films, and multilayer structures were produced in the same manner as in Example 1, and various measurements and evaluations were carried out. The results are shown in Table 2.
• Example 7 Except for changing the aluminum metal deposition layer to a silica (SiOx) deposition layer, resin composition pellets, coextruded films, composite films, and multilayer structures were produced in the same manner as in Example 1, and various measurements and evaluations were carried out. The results are shown in Table 2.
• Example 8 Except for not using magnesium stearate, resin composition pellets, a co-extruded film, a composite film and a multi-layer structure were produced in the same manner as in Example 1, and various measurements and evaluations were carried out. The results are shown in Table 2.
• Example 9 to 10 Resin composition pellets, coextruded films, composite films and multilayer structures were prepared in the same manner as in Example 1, except that the amount of magnesium stearate kneaded with EVOH (c-1), calculated as magnesium ions, was changed as shown in Table 1, and various measurements and evaluations were carried out. The results are shown in Table 2.
• Example 11 Except for changing the magnesium stearate kneaded with EVOH (c-1) to calcium stearate (Ca-St) (Example 11) or zinc stearate (Zn-St) (Example 12), resin composition pellets, co-extruded films, composite films and multilayer structures were produced in the same manner as in Example 1, and various measurements and evaluations were carried out. The results are shown in Table 2.
• Example 13 Resin composition pellets, coextruded films, composite films and multilayer structures were prepared in the same manner as in Example 1, except that polyethylene (e-2) (linear low density polyethylene (mLLDPE) "Evolue (trademark) SP1510" (MFR (190°C, 2.16 kg load) 1.0 g/10 min, density 0.915 g/cm 3 ) polymerized with a metallocene catalyst, manufactured by Prime Polymer Co., Ltd.) was used instead of polyethylene (e-1), and various measurements and evaluations were performed. The results are shown in Table 2.
• polyethylene e-2
• mLLDPE linear low density polyethylene
• Example 14 Resin composition pellets, coextruded films, composite films and multilayer structures were prepared in the same manner as in Example 1, except that polyethylene (e-3) (high density polyethylene (HDPE) "Novatec (trademark) HD HY540" (MFR (190°C, 2.16 kg load) 1.0 g/10 min, density 0.960 g/cm 3 ) manufactured by Japan Polyethylene Corporation) was used instead of polyethylene (e-1), and various measurements and evaluations were carried out. The results are shown in Table 2.
• polyethylene e-3
• HDPE high density polyethylene
• HD HY540 MFR (190°C, 2.16 kg load) 1.0 g/10 min, density 0.960 g/cm 3
• e-1 high density polyethylene
• Example 15 Except for changing the average thickness of the barrier resin layer (C) to 12 ⁇ m, resin composition pellets, a coextruded film, a composite film, and a multilayer structure were produced in the same manner as in Example 1, and various measurements and evaluations were carried out. The results are shown in Table 2.
• Example 16 Except for changing the average thickness of the moisture-proof resin layer (E) to 52 ⁇ m, resin composition pellets, coextruded films, composite films, and multilayer structures were prepared in the same manner as in Example 1, and various measurements and evaluations were carried out. The results are shown in Table 2.
• Example 17 Except for laminating the paper layer and the composite film by a known dry lamination instead of extrusion lamination, resin composition pellets, co-extruded film, composite film, and multilayer structure were produced in the same manner as in Example 1, and various measurements and evaluations were carried out. The results are shown in Table 2. A two-liquid reactive polyurethane adhesive was used as the adhesive for dry lamination, and was used so that the average thickness after drying would be 4 ⁇ m.
• Example 18 A multilayer structure was produced by laminating a linear low-density polyethylene layer having an average thickness of 30 ⁇ m as a moisture-proof resin layer (F) on the exposed surface of the paper layer (A) of the multilayer structure obtained by the same procedure as in Example 1, by extruding linear low-density polyethylene (LLDPE) "LUMITAC (trademark) BL 600K” (MFR (190°C, 2.16 kg load) 21 g/10 min, density 0.898 g/ cm3 ) manufactured by Tosoh Corporation at 300°C. The results are shown in Table 2.
• LLDPE linear low-density polyethylene
• EVOH (c-4) (ethylene unit content 44 mol%, saponification degree 99.99 mol%, epoxypropane modification degree 4.6 mol%, MFR (190° C., 2.16 kg load) 5.6 g/10 min, containing 220 ppm of sodium acetate calculated as sodium ions, 30 ppm of phosphate ions calculated as phosphate radicals, 150 ppm of boric acid calculated as boron element, and 30 ppm of zinc acetate calculated as zinc ions) was used in place of EVOH (c-1).
• Example 21 A multilayer structure was produced by laminating a linear low-density polyethylene layer having an average thickness of 30 ⁇ m as a moisture-proof resin layer (F) on the exposed surface of the moisture-proof resin layer (E) of the multilayer structure obtained by the same procedure as in Example 20, which was obtained by extruding linear low-density polyethylene (LLDPE) "LUMITAC (trademark) BL 600K” (MFR (190°C, 2.16 kg load) 21 g/10 min, density 0.898 g /cm3) manufactured by Tosoh Corporation at 300°C. The results are shown in Table 2.
• LLDPE linear low-density polyethylene
• Example 22 Except for using white paper having a basis weight of 50 g/ m2 as the paper layer (A), resin composition pellets, coextruded films, composite films, and multilayer structures were prepared in the same manner as in Example 1, and various measurements and evaluations were carried out. The results are shown in Table 2.
• Example 23 Except for using white paper having a basis weight of 80 g/ m2 as the paper layer (A), resin composition pellets, coextruded films, composite films, and multilayer structures were prepared in the same manner as in Example 1, and various measurements and evaluations were carried out. The results are shown in Table 2.
• Example 24 Except for using white paper having a basis weight of 150 g/ m2 as the paper layer (A), resin composition pellets, coextruded films, composite films, and multilayer structures were prepared in the same manner as in Example 1, and various measurements and evaluations were carried out. The results are shown in Table 2.
• Example 25 In producing the multilayer structure, the moisture-proof resin layer (E) and the paper layer (A) of the composite film were laminated via the thermoplastic resin layer (X), and a moisture-proof resin layer (F) was further provided on the exposed inorganic vapor deposition layer (B).
• resin composition pellets, co-extruded film, composite film and multilayer structure were produced and various measurements and evaluations were carried out. The results are shown in Table 2.
• Example 1 Resin composition pellets, composite films and multilayer structures were produced in the same manner as in Example 1, except that the following composite films were produced and used instead of the composite film produced in Example 1, and various measurements and evaluations were carried out. Without laminating the barrier resin layer (C) and adhesive resin layer (D), a single-layer film of a moisture-proof resin layer (E) having an average thickness of 40 ⁇ m was used, one side of the moisture-proof resin layer (E) was subjected to a corona discharge treatment by a known method, and an aluminum metal vapor deposition layer was laminated on the corona discharge treated side to produce a composite film. The results are shown in Table 2.
• 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), the metal species and content of the 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 also shows the layer structure and average thickness of each layer in each multilayer structure, the stretch ratio (MD x TD) of the coextruded film, 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 parts other than the paper layer), together with the evaluation results.
• each of the multilayer structures of Examples 1 to 25 had high gas barrier properties both before and after folding, and it was possible to form paper containers with sufficient strength even in low-temperature environments, and it was confirmed that the occurrence of defects during recycling was suppressed.
• the multilayer structure of the present invention can be suitably used as a molding material for paper containers such as liquid paper containers.

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