Gas barrier film, laminate, and packaging material

Abstract

To provide a gas barrier film capable of constituting a laminate in which a base material and a heat seal layer sufficiently adhere to each other and which is easily recycled.SOLUTION: The gas barrier film 10 includes a substrate 11 which is an unstretched film containing polyethylene, and an inorganic layer 13 formed on the 11a side of the first surface of the substrate 11. The first surface 11a is made of polyethylene, and the probe descent temperature on the first surface side of the substrate 11 is 150 °C or more and 180 °C or less. The proportion of polyethylene in the entire gas barrier film is 90% by mass or more, and the gas barrier film does not include a layer containing water-swelling mica.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a gas barrier film, and also to a laminate and a packaging material using the gas barrier film. [Background technology]

[0002] Packaging materials used for packaging foods, pharmaceuticals, etc. are required to have gas barrier properties, i.e., the ability to prevent the intrusion of gases (water vapor, oxygen, etc.) that denature the contents, in order to prevent deterioration and spoilage of the contents and maintain their functionality and quality. For this reason, film materials with gas barrier properties (gas barrier films) are used for these packaging materials.

[0003] Known gas barrier films include those in which a gas barrier layer made of a material with gas barrier properties is provided on the surface of a resin substrate. Known gas barrier layers include metal foils, metal vapor deposition films, and films formed by wet coating. Known films that exhibit oxygen barrier properties include resin films formed from coating agents containing water-soluble polymers, resins such as polyvinylidene chloride, and inorganic layered mineral composite resin films formed from coating agents containing water-soluble polymers and inorganic layered minerals (Patent Document 1). Other proposed gas barrier layers include a gas barrier layer formed by sequentially laminating a vapor-deposited thin film layer made of an inorganic oxide and a gas barrier composite coating containing a water-soluble polymer, an inorganic layered compound, and a metal alkoxide (Patent Document 2), and a gas barrier layer containing a polyvalent metal salt of a carboxylic acid, which is a reaction product of a carboxy group of a polycarboxylic acid polymer and a polyvalent metal compound (Patent Document 3).

[0004] In recent years, growing environmental awareness stemming from the problem of marine plastic waste has led to calls for more efficient sorting and recycling of plastic materials. Packaging laminates, which have traditionally been made high performance by combining a variety of different materials, are no exception, and there is now a demand for mono-materialization.

[0005] To achieve a mono-material laminate, the resin materials of the films that make up each layer must be of the same type. For example, polyethylene, a type of polyolefin, is widely used in packaging materials, so there are high hopes for a mono-material laminate using polyethylene.

[0006] To achieve mono-materialization, for example, Patent Document 4 proposes a laminate using a polyethylene film having a vapor deposition layer on at least one side of the substrate and heat seal layer, and discloses stretched polyethylene as the substrate from the viewpoint of printability and bag-making suitability. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Patent No. 6191221 [Patent Document 2] Japanese Patent Application Laid-Open No. 2000-254994 [Patent Document 3] Patent No. 4373797 [Patent Document 4] Japanese Patent Application Publication No. 2020-055157 Summary of the Invention [Problem to be solved by the invention]

[0008] However, the stretched polyethylene substrate proposed in Patent Document 4 has a problem in that the peel strength of the substrate surface layer is weak, and the heat seal layer bonded via the adhesive layer is easily peeled off. Therefore, it can only be used for light packaging materials that do not require high adhesive strength, and is not suitable for packaging materials for boiling treatment, etc., which require sufficient durability. The inventors have solved this problem while maintaining a mono-material structure.

[0009] In view of the above circumstances, an object of the present invention is to provide a gas barrier film that can form a laminate in which the substrate and the heat seal layer are sufficiently adhered to each other and which is easy to recycle. [Means for solving the problem]

[0010] A first aspect of the present invention is a gas barrier film comprising an unstretched film containing polyethylene and an inorganic oxide layer formed on a first surface side of the unstretched film. The first surface of the unstretched film is made of polyethylene. This gas barrier film has a probe drop temperature of 150°C or higher and 180°C or lower on the first surface side of the unstretched film. The proportion of polyethylene in the entire gas barrier film is 90 mass % or more. This gas barrier film does not include a layer containing water-swellable mica.

[0011] A second aspect of the present invention is a laminate comprising the gas barrier film according to the first aspect and a heat seal layer containing polyethylene and joined to the gas barrier film so as to sandwich an inorganic oxide layer between the gas barrier film and an unstretched film. The proportion of polyethylene in the entire laminate is 90% by mass or more. A third aspect of the present invention is a packaging material formed using the laminate according to the second aspect. [Effects of the Invention]

[0012] According to the present invention, a gas barrier film can be provided which allows for sufficient adhesion between the substrate and the heat seal layer and allows for the formation of a laminate which is easy to recycle. [Brief explanation of the drawings]

[0013] [Figure 1] 1 is a schematic cross-sectional view of a laminate according to one embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0014] Hereinafter, one embodiment of the present invention will be described with reference to FIG. 1 is a schematic cross-sectional view of a laminate 1 according to this embodiment. The laminate 1 includes a gas barrier film 10 and a heat seal layer 30. The gas barrier film 10 of this embodiment is one aspect of the gas barrier film according to the present invention. The gas barrier film 10 and the heat seal layer 30 are joined by an adhesive layer 20 . The proportion of polyethylene in the laminate 1 is 90% by mass or more, which makes the laminate 1 a highly recyclable mono-material.

[0015] The gas barrier film 10 comprises a sheet-like substrate 11, an inorganic oxide layer 13, and an oxygen barrier coating 14, which are formed in this order on a first surface 11a of the substrate 11. At least one of the inorganic oxide layer 13 and the oxygen barrier film 14 is sufficient, and both may be present as shown in FIG. The proportion of polyethylene in the gas barrier film 10 is 90% by mass or more, which makes the gas barrier film 10 a highly recyclable mono-material. Each component of the gas barrier film 10 will be described below.

[0016] The substrate 11 includes polyethylene (PE). The substrate 11 may be a single-layer film made of a single resin, or a single-layer or laminated film made of multiple resins. Alternatively, the substrate 11 may be one in which PE is laminated on another substrate (metal, wood, paper, ceramics, etc.). In other words, the substrate 11 may be a single layer, or two or more layers.

[0017] The substrate 11 may be a single-layer film made of a single resin, or a single-layer or laminated film made of multiple resins. Furthermore, the substrate 11 may be one in which the above-mentioned various resins are laminated on another substrate (metal, wood, paper, ceramics, etc.). In other words, the substrate 11 may be a single layer, or two or more layers.

[0018] The substrate 11 may be an unstretched film or a stretched film such as a uniaxially stretched or biaxially stretched film. The density of the PE contained in the substrate 11 is preferably 0.935 or more, and more preferably 0.940 or more. When the density of the PE is within the above range, the substrate 11 is easily prevented from being stretched and wrinkled during rolling, and the inorganic oxide layer 13 is easily prevented from being cracked. PE may be at least one type of polymer selected from homopolymer, random copolymer, and block copolymer. Homopolymer is polyethylene consisting only of polyethylene unit. Random copolymer is polyethylene in which the main monomer ethylene and a small amount of a comonomer different from ethylene (e.g., α-olefin) are randomly copolymerized to form a homogeneous phase. Block copolymer is polyethylene in which the main monomer ethylene and the comonomer (e.g., α-olefin) are copolymerized in blocks or polymerized in a rubber-like manner to form a heterogeneous phase.

[0019] The substrate 11 may have a multilayer structure including multiple layers (films) each containing PE of different densities. It is desirable to appropriately multilayer the substrate 11, taking into consideration the processability, rigidity, stiffness, heat resistance, and powder shedding during transport of the films constituting each layer. The films constituting the substrate 11 can be made using an appropriate selection of high-density polyolefin, medium-density polyolefin, low-density polyolefin, etc. In this case, too, it is preferable that the density of the substrate 11 as a whole be 0.935 or higher. Each layer of the substrate 11 may contain a slip agent, an antistatic agent, etc., and the content or content ratio of these may vary from layer to layer. The substrate 11 having multiple layers can be produced by extrusion coating, co-extrusion coating, sheet molding, co-extrusion blow molding, etc. The first surface 11a of the substrate 11 may be subjected to a surface treatment such as chemical treatment, solvent treatment, corona treatment, low-temperature plasma treatment, or ozone treatment in order to improve adhesion to the inorganic oxide layer 13. Furthermore, a similar surface treatment may be applied to the second surface 11b opposite to the first surface 11a in order to bond it to a printing substrate.

[0020] An undercoat layer may be provided on the first surface 11a. The undercoat layer is a layer containing an organic polymer as a main component and is sometimes called a primer layer. The provision of the undercoat layer can improve the film-forming properties and adhesion strength of the inorganic oxide layer 13 and the oxygen barrier coating 14. The content of the organic polymer in the undercoat layer may be, for example, 70% by mass or more, or 80% by mass or more. Examples of organic polymers include polyacrylic resin, polyester resin, polycarbonate resin, polyurethane resin, polyamide resin, polyolefin resin, polyimide resin, melamine resin, and phenolic resin. In consideration of the hot water resistance of the adhesive strength between the substrate 11 and the inorganic oxide layer 13, it is preferable that the undercoat layer contain at least one of the above polyacrylic resin, polyol resin, polyurethane resin, polyamide resin, or reaction products of these organic polymers. The undercoat layer may contain a silane coupling agent, an organic titanate, a modified silicone oil, or the like.

[0021] The organic polymer used in the undercoat layer is more preferably an organic polymer having a urethane bond formed by the reaction of a polyol having two or more hydroxyl groups at its terminal with an isocyanate compound, or an organic polymer containing a reaction product of a polyol having two or more hydroxyl groups at its terminal with an organic silane compound such as a silane coupling agent or its hydrolyzate. Either one or both of these may be used.

[0022] Examples of the polyols include at least one selected from acrylic polyol, polyvinyl acetal, polystyrene polyol, and polyurethane polyol. The acrylic polyol may be obtained by polymerizing an acrylic acid derivative monomer, or may be obtained by copolymerizing an acrylic acid derivative monomer with another monomer. Examples of the acrylic acid derivative monomer include ethyl methacrylate, hydroxyethyl methacrylate, hydroxypropyl methacrylate, and hydroxybutyl methacrylate. Examples of the monomer copolymerized with the acrylic acid derivative monomer include styrene. The isocyanate compound reacts with the polyol to form a urethane bond, thereby enhancing the adhesion between the substrate 11 and the inorganic oxide layer 13. In other words, the isocyanate compound functions as a crosslinking agent or a curing agent. Examples of the isocyanate compound include aromatic monomers such as tolylene diisocyanate (TDI), diphenylmethane diisocyanate (MDI), aliphatic monomers such as xylene diisocyanate (XDI), hexamethylene diisocyanate (HMDI), and isophorone diisocyanate (IPDI), as well as polymers and derivatives thereof. The above-mentioned isocyanate compounds may be used singly or in combination of two or more.

[0023] Examples of silane coupling agents include vinyltrimethoxysilane, γ-chloropropylmethyldimethoxysilane, γ-chloropropyltrimethoxysilane, glycidoxypropyltrimethoxysilane, γ-methacryloxypropyltrimethoxysilane, and γ-methacryloxypropylmethyldimethoxysilane. The organic silane compound may be a hydrolyzate of these silane coupling agents. The organic silane compound may contain one of the above-mentioned silane coupling agents and their hydrolyzates alone, or two or more of them in combination.

[0024] The undercoat layer can be formed using a mixture of the above-mentioned components in an organic solvent in any desired ratio. The mixture may contain, for example, a curing accelerator such as a tertiary amine, an imidazole derivative, a metal salt compound of a carboxylic acid, a quaternary ammonium salt, or a quaternary phosphonium salt; an antioxidant such as a phenol, sulfur, or phosphite; a leveling agent; a flow adjuster; a catalyst; a crosslinking accelerator; a filler; etc. The mixed liquid can be applied in the form of a layer on the substrate 11 by a known printing method such as offset printing, gravure printing, or silk screen printing, or a known coating method such as roll coating, knife edge coating, or gravure coating. After application, the mixture can be heated to, for example, 50 to 200°C to form an undercoat layer.

[0025] There are no particular limitations on the thickness of the undercoat layer, and it can be, for example, 0.005 to 5 μm. The thickness can be appropriately determined depending on the application and desired properties. The thickness of the undercoat layer is preferably 0.01 to 1 μm, and more preferably 0.01 to 0.5 μm. If the thickness of the undercoat layer is 0.01 μm or more, sufficient adhesion strength between the substrate 11 and the inorganic oxide layer 13 is obtained, and oxygen barrier properties are also good. If the thickness of the undercoat layer is 1 μm or less, it is easy to form a uniform coated surface, and drying load and production costs can be reduced.

[0026] The substrate 11 may contain additives such as fillers, antiblocking agents, antistatic agents, plasticizers, lubricants, antioxidants, etc. These additives may be used alone or in combination of two or more.

[0027] There is no particular limitation on the thickness of the substrate 11, and it can be appropriately determined according to the price and application, taking into consideration suitability as a packaging material and suitability for laminating other films. The thickness of the substrate 11 is preferably 3 μm to 200 μm in practice, more preferably 5 μm to 120 μm, even more preferably 6 μm to 100 μm, and particularly preferably 10 μm to 40 μm.

[0028] (Inorganic oxide layer 13) Examples of inorganic oxides constituting the inorganic oxide layer 13 include aluminum oxide, silicon oxide, magnesium oxide, titanium oxide, tin oxide, zinc oxide, and indium oxide. Aluminum oxide or silicon oxide is particularly preferred because of its excellent productivity and excellent oxygen barrier and water vapor barrier properties in heat resistance and moist heat resistance. The inorganic oxide layer 13 may be formed of one type of inorganic oxide, or may be formed of two or more appropriately selected inorganic oxides.

[0029] The thickness of the inorganic oxide layer 13 can be 1 nm or more and 200 nm or less. If the thickness is 1 nm or more, excellent oxygen barrier properties and water vapor barrier properties can be obtained. If the thickness is 200 nm or less, manufacturing costs can be kept low, cracks caused by external forces such as bending or pulling are less likely to occur, and deterioration of the barrier properties can be suppressed. The inorganic oxide layer 13 can be formed by a known film formation method such as vacuum deposition, sputtering, ion plating, or plasma vapor deposition (CVD).

[0030] (Oxygen barrier film 14) The oxygen barrier film 14 can be a known film formed by a wet coating method. The oxygen barrier film 14 is obtained by forming a coating film made of a coating agent on the substrate 11 or the inorganic oxide layer 13 by a wet coating method and drying the coating film. In this specification, the term "coating film" refers to a wet film, and the term "film" refers to a dry film.

[0031] The oxygen barrier film 14 may include a film containing at least one of a metal alkoxide, its hydrolysate, or its reaction product, and a water-soluble polymer (hereinafter, sometimes referred to as an "organic-inorganic composite film.") It is preferable that the film further includes at least one of a silane coupling agent and its hydrolysate.

[0032] Examples of metal alkoxides and their hydrolysates contained in the organic-inorganic composite coating include those represented by the general formula M(OR), such as tetraethoxysilane [Si(OC2H5)4] and triisopropoxyaluminum [Al(OC3H7)3]. n and hydrolysates thereof. Only one of these may be contained, or two or more of them may be contained in appropriate combination.

[0033] The total content of at least one of the metal alkoxide and its hydrolysate, or reaction product thereof in the organic-inorganic composite coating is, for example, 40 to 70 mass %. From the viewpoint of further reducing oxygen permeability, the lower limit of this total content may be 50 mass % and the upper limit of this total content may be 65 mass %.

[0034] The water-soluble polymer contained in the organic-inorganic composite coating is not particularly limited, and examples thereof include various polymers such as polyvinyl alcohol, polysaccharides such as starch, methyl cellulose, and carboxymethyl cellulose, and acrylic polyols. From the viewpoint of further improving oxygen gas barrier properties, it is preferable to include a polyvinyl alcohol polymer. The number-average molecular weight of the water-soluble polymer is, for example, 40,000 to 180,000.

[0035] A water-soluble polymer such as polyvinyl alcohol can be obtained by, for example, saponifying (including partial saponification) polyvinyl acetate. This water-soluble polymer may have several tens of percent or only a few percent of acetate groups remaining.

[0036] The content of the water-soluble polymer in the organic-inorganic composite film is, for example, 15 to 50 mass %. If the content of the water-soluble polymer is 20 to 45 mass %, the oxygen permeability of the organic-inorganic composite film can be further reduced, which is preferable.

[0037] Silane coupling agents and their hydrolysates contained in the organic-inorganic composite coating include silane coupling agents having an organic functional group. Examples of such silane coupling agents and their hydrolysates include ethyltrimethoxysilane, vinyltrimethoxysilane, γ-chloropropylmethyldimethoxysilane, γ-chloropropyltrimethoxysilane, glycidoxypropyltrimethoxysilane, γ-methacryloxypropyltrimethoxysilane, γ-methacryloxypropylmethyldimethoxysilane, and their hydrolysates. Only one of these may be contained, or two or more may be contained in appropriate combination.

[0038] At least one of the silane coupling agent and its hydrolysate preferably has an epoxy group as an organic functional group. Examples of silane coupling agents having an epoxy group include γ-glycidoxypropyltrimethoxysilane and β-(3,4-epoxycyclohexyl)ethyltrimethoxysilane. The silane coupling agent having an epoxy group and its hydrolysate may have an organic functional group other than the epoxy group, such as a vinyl group, an amino group, a methacryl group, or a ureyl group.

[0039] The silane coupling agent having an organic functional group and its hydrolysate can further improve the oxygen barrier properties of the oxygen barrier coating 14 and the adhesion to the substrate 11 or the inorganic oxide layer 13 through the interaction between the organic functional group and the hydroxyl group of the water-soluble polymer. In particular, the interaction between the epoxy groups of the silane coupling agent and its hydrolysate and the hydroxyl groups of the polyvinyl alcohol can form an oxygen barrier coating 14 that is particularly excellent in oxygen barrier properties and adhesion.

[0040] The total content of the silane coupling agent and its hydrolysate or reaction product thereof in the organic-inorganic composite coating is, for example, 1 to 15 mass %. If the total content of the silane coupling agent and its hydrolysate or reaction product thereof is 2 to 12 mass %, the oxygen permeability of the organic-inorganic composite coating can be further reduced, which is preferable.

[0041] The organic-inorganic composite coating may contain a crystalline inorganic layered compound having a layered structure. Examples of the inorganic layered compound include clay minerals such as kaolinite, smectite, and mica. These can be used alone or in appropriate combinations of two or more. The particle size of the inorganic layered compound is, for example, 0.1 to 10 μm. The aspect ratio of the inorganic layered compound is, for example, 50 to 5,000.

[0042] As the inorganic layered compound, a smectite clay mineral is preferred because it can form a film with excellent oxygen barrier properties and adhesive strength by allowing a water-soluble polymer to penetrate between the layers of the layered structure (intercalation).Specific examples of smectite clay minerals include montmorillonite, hectorite, saponite, and water-swellable synthetic mica.

[0043] Another preferred example of the oxygen barrier film 14 is a film containing a polyvalent metal salt of carboxylic acid, which is a reaction product between the carboxyl groups of a polycarboxylic acid polymer (A) and a polyvalent metal compound (B) (a polyvalent metal salt of polycarboxylic acid film). In this case, the film may be a polyvalent metal salt of polycarboxylic acid film formed by applying a coating agent containing a mixture of a polycarboxylic acid polymer (A) and a polyvalent metal compound (B) and drying it by heating, or a polyvalent metal salt of polycarboxylic acid film formed by applying a coating agent containing a polycarboxylic acid polymer (A) as the main component and drying it to form a film A, applying a coating agent containing a polyvalent metal compound (B) as the main component, and drying it to form a film B, and then causing a crosslinking reaction between the A and B layers.

[0044] [Polycarboxylic acid polymer (A)] A polycarboxylic acid polymer is a polymer having two or more carboxyl groups in the molecule. Examples of polycarboxylic acid polymers include (co)polymers of ethylenically unsaturated carboxylic acids, copolymers of ethylenically unsaturated carboxylic acids with other ethylenically unsaturated monomers, and acidic polysaccharides having carboxyl groups in the molecule, such as alginic acid, carboxymethylcellulose, and pectin. Examples of the ethylenically unsaturated carboxylic acid include acrylic acid, methacrylic acid, itaconic acid, maleic acid, fumaric acid, and crotonic acid. Examples of the ethylenically unsaturated monomer copolymerizable with the ethylenically unsaturated carboxylic acid include ethylene, propylene, saturated carboxylic acid vinyl esters such as vinyl acetate, alkyl acrylates, alkyl methacrylates, alkyl itaconates, vinyl chloride, vinylidene chloride, styrene, acrylamide, and acrylonitrile. These polycarboxylic acid polymers may be used singly or in combination of two or more.

[0045] Among the above, from the viewpoint of the gas barrier properties of the resulting gas barrier film, preferred components are polymers containing a structural unit derived from at least one polymerizable monomer selected from the group consisting of acrylic acid, maleic acid, methacrylic acid, itaconic acid, fumaric acid, and crotonic acid, and particularly preferred are polymers containing a structural unit derived from at least one polymerizable monomer selected from the group consisting of acrylic acid, maleic acid, methacrylic acid, and itaconic acid. In this polymer, the proportion of structural units derived from at least one polymerizable monomer selected from the group consisting of acrylic acid, maleic acid, methacrylic acid, and itaconic acid is preferably 80 mol % or more, and more preferably 90 mol % or more (where the total of all structural units constituting the polymer is 100 mol %). The polymer may be a homopolymer or a copolymer. When the polymer is a copolymer containing other structural units in addition to the above structural units, examples of the other structural units include structural units derived from ethylenically unsaturated monomers copolymerizable with the above-mentioned ethylenically unsaturated carboxylic acids.

[0046] The number-average molecular weight of the polycarboxylic acid polymer is preferably within the range of 2,000 to 10,000,000, and more preferably 5,000 to 1,000,000. If the number-average molecular weight is less than 2,000, the resulting gas barrier film will not achieve sufficient water resistance, and moisture may deteriorate the gas barrier properties and transparency, or whitening may occur. On the other hand, if the number-average molecular weight exceeds 10,000,000, the viscosity of the coating agent used to form the oxygen barrier film may increase, impairing coatability. The number average molecular weight is determined by gel permeation chromatography (GPC) and is calculated as polystyrene.

[0047] When a coating agent containing a polycarboxylic acid polymer (A) as a main component is applied and dried to form a coating A, and then the coating B is formed, some of the carboxy groups of the polycarboxylic acid polymer may be neutralized in advance with a basic compound. By neutralizing some of the carboxy groups of the polycarboxylic acid polymer in advance, the water resistance and heat resistance of the coating A can be further improved. The basic compound is preferably at least one basic compound selected from the group consisting of polyvalent metal compounds, monovalent metal compounds, and ammonia. As the polyvalent metal compound, the compounds exemplified in the description of the polyvalent metal compound (B) below can be used. As the monovalent metal compound, for example, sodium hydroxide, potassium hydroxide, etc. can be mentioned.

[0048] Various additives can be added to the coating agent containing the polycarboxylic acid polymer (A) as the main component, and examples of such additives include crosslinking agents, curing agents, leveling agents, antifoaming agents, antiblocking agents, antistatic agents, dispersants, surfactants, softeners, stabilizers, film-forming agents, and thickeners, provided that the barrier performance is not impaired.

[0049] The solvent used in the coating agent containing the polycarboxylic acid polymer (A) as the main component is preferably an aqueous medium. Examples of the aqueous medium include water, a water-soluble or hydrophilic organic solvent, or a mixture thereof. The aqueous medium is usually water or a medium containing water as the main component. The water content in the aqueous medium is preferably 70% by mass or more, more preferably 80% by mass or more. Examples of water-soluble or hydrophilic organic solvents include alcohols such as methanol, ethanol, and isopropanol, ketones such as acetone and methyl ethyl ketone, ethers such as tetrahydrofuran, cellosolves, carbitols, and nitriles such as acetonitrile.

[0050] [Polyvalent metal compounds (B)] The polyvalent metal compound is not particularly limited as long as it is a compound that reacts with the carboxyl groups of the polycarboxylic acid polymer to form a polyvalent metal salt of polycarboxylic acid, and examples thereof include zinc oxide particles, magnesium oxide particles, magnesium methoxide, copper oxide, calcium carbonate, etc. These may be used alone or in combination. Zinc oxide is preferred from the viewpoint of the oxygen barrier properties of the oxygen barrier coating.

[0051] Zinc oxide is an inorganic material capable of absorbing ultraviolet light. The average particle size of the zinc oxide particles is not particularly limited, but from the viewpoints of gas barrier properties, transparency, and coating suitability, the average particle size is preferably 5 μm or less, more preferably 1 μm or less, and particularly preferably 0.1 μm or less.

[0052] When a coating agent containing a polyvalent metal compound (B) as a main component is applied and dried to form a B film, various additives may be added in addition to zinc oxide particles as needed, provided that the effects of the present invention are not impaired. Such additives may include a resin soluble or dispersible in the solvent used in the coating agent, a dispersant soluble or dispersible in the solvent, a surfactant, a softener, a stabilizer, a film-forming agent, a thickener, etc.

[0053] Among the above, it is preferable to contain a resin that is soluble or dispersible in the solvent used in the coating agent. This improves the coatability and film-forming properties of the coating agent. Examples of such resins include alkyd resins, melamine resins, acrylic resins, urethane resins, polyester resins, phenolic resins, amino resins, fluororesins, epoxy resins, and isocyanate resins.

[0054] It is also preferable to include a dispersant that is soluble or dispersible in the solvent used in the coating agent. This improves the dispersibility of the polyvalent metal compound. Anionic surfactants or nonionic surfactants can be used as the dispersant. Examples of such surfactants include (poly)carboxylates, alkyl sulfates, alkylbenzene sulfonates, alkylnaphthalene sulfonates, alkyl sulfosuccinates, alkyl diphenyl ether disulfonates, alkyl phosphates, aromatic phosphate esters, polyoxyethylene alkyl ethers, polyoxyethylene alkylphenol ethers, polyoxyethylene alkyl esters, alkyl allyl sulfates, polyoxyethylene alkyl phosphate esters, sorbitan alkyl esters, glycerin fatty acid esters, sorbitan fatty acid esters, sucrose fatty acid esters, polyethylene glycol fatty acid esters, polyoxyethylene sorbitan alkyl esters, polyoxyethylene alkyl allyl ethers, polyoxyethylene derivatives, polyoxyethylene sorbitol fatty acid esters, polyoxy fatty acid esters, and polyoxyethylene alkylamines. These surfactants may be used alone or in combination.

[0055] When an additive is contained in a coating agent containing a polyvalent metal compound (B) as a main component, the mass ratio of the polyvalent metal compound to the additive (polyvalent metal compound:additive) is preferably within a range of 30:70 to 99:1, and more preferably within a range of 50:50 to 98:2.

[0056] Examples of solvents used in coating agents containing polyvalent metal compound (B) as a main component include water, methyl alcohol, ethyl alcohol, isopropyl alcohol, n-propyl alcohol, n-butyl alcohol, n-pentyl alcohol, dimethyl sulfoxide, dimethylformamide, dimethylacetamide, toluene, hexane, heptane, cyclohexane, acetone, methyl ethyl ketone, diethyl ether, dioxane, tetrahydrofuran, ethyl acetate, and butyl acetate. These solvents may be used alone or in combination of two or more. Among these, methyl alcohol, ethyl alcohol, isopropyl alcohol, toluene, ethyl acetate, methyl ethyl ketone, and water are preferred from the viewpoint of coatability, and methyl alcohol, ethyl alcohol, isopropyl alcohol, and water are preferred from the viewpoint of manufacturability.

[0057] When a coating agent containing a polycarboxylic acid polymer (A) and a polyvalent metal compound (B) is applied and dried to form a polycarboxylic acid polyvalent metal salt film, the polycarboxylic acid polyvalent metal salt film can be formed by mixing the polycarboxylic acid polymer (A), the polyvalent metal compound (B), a resin or dispersant soluble or dispersible in water or an alcohol as a solvent, and additives as needed, and applying and drying the resulting coating agent by a known coating method. Examples of coating methods include casting, dipping, roll coating, gravure coating, screen printing, reverse coating, spray coating, kit coating, die coating, metaling bar coating, chamber doctor combined coating, and curtain coating.

[0058] The thickness of the oxygen barrier film 14 is set according to the required oxygen barrier properties and can be, for example, 0.05 to 5 μm, preferably 0.05 to 1 μm, and more preferably 0.1 to 0.5 μm. If the thickness of the oxygen barrier film 14 is 0.05 μm or more, sufficient oxygen barrier properties are likely to be obtained. If the thickness of the oxygen barrier film 14 is 1 μm or less, it is easy to form a uniform coated surface, and drying load and production costs can be reduced.

[0059] The oxygen barrier film 14, which is made of an organic-inorganic composite film or a polyvalent metal salt film of polycarboxylic acid, maintains excellent oxygen barrier properties even after boiling or retort sterilization. The laminate 1, in which a sealant film is bonded to a gas barrier film 10, has sufficient adhesion and sealing strength for use as a packaging material for boiling or retort treatment. It also offers transparency, flex resistance, and stretch resistance not found in metal foils or metal-deposited films. Another advantage is that it poses no risk of generating harmful substances such as dioxins.

[0060] (adhesive layer 20) A known dry laminating adhesive can be used as the adhesive layer 20. There are no particular restrictions on the dry laminating adhesive that can be used, and specific examples include two-component curing ester-based adhesives, ether-based adhesives, and urethane-based adhesives.

[0061] A gas barrier adhesive that exhibits gas barrier properties after curing can also be used for the adhesive layer 20. By using a gas barrier adhesive, the gas barrier properties of the laminate 1 can be improved. The oxygen permeability of the gas barrier adhesive is 150 cc / m 2 ·day·atm or less is preferable, and 100cc / m 2 ·day·atm or less is more preferable, and 80cc / m 2 ·day·atm or less is more preferable, and 50cc / m 2By having the oxygen permeability within the above range, the gas barrier properties of the laminate 1 can be sufficiently improved, and even if minor cracks or the like occur in the inorganic oxide layer 13 or the oxygen barrier film 14, the gas barrier adhesive can penetrate into the gaps, thereby preventing a decrease in the gas barrier properties. Examples of gas barrier adhesives include epoxy adhesives, polyester / polyurethane adhesives, etc. Specific examples of gas barrier adhesives include "Maxieve" manufactured by Mitsubishi Gas Chemical Company, Inc. and "Paslim" manufactured by DIC Corporation.

[0062] When the adhesive layer 20 is made of a gas barrier adhesive, its thickness is preferably at least 50 times the thickness of the inorganic oxide layer 13. By having a thickness within the above range, cracking of the inorganic oxide layer 13 can be more sufficiently suppressed, and the gas barrier properties of the laminate 1 can be further improved. Furthermore, the adhesive layer 20 can be imparted with cushioning properties that absorb external impacts, preventing the inorganic oxide layer 13 from cracking due to impact. From the viewpoints of maintaining the flexibility of the laminate 1, processability, and cost, the thickness is preferably no more than 300 times the thickness of the inorganic oxide layer 13. When expressed numerically, such thickness is, for example, 0.1 to 20 μm, preferably 0.5 to 10 μm, and more preferably 1 to 5 μm.

[0063] The adhesive forming the adhesive layer 20 can be applied by, for example, bar coating, dipping, roll coating, gravure coating, reverse coating, air knife coating, comma coating, die coating, screen printing, spray coating, gravure offset, or the like. The temperature for drying the adhesive coating can be, for example, 30 to 200°C, and preferably 50 to 180°C. The temperature for curing the coating can be, for example, room temperature to 70°C, and preferably 30 to 60°C. By keeping the drying and curing temperatures within the above ranges, it is possible to further suppress the occurrence of cracks in the inorganic oxide layer 13 and the adhesive layer 20, and to achieve excellent gas barrier properties.

[0064] From the viewpoint of preventing cracking of the inorganic oxide layer 13, it is preferable that the adhesive layer 20 and the inorganic oxide layer 13 are in direct contact with each other, but another layer may be present between the adhesive layer 20 and the inorganic oxide layer 13.

[0065] (heat seal layer 30) The heat seal layer 30 is a layer containing polyolefin, and functions as a sealant when a packaging bag or the like is produced using the laminate 1. A polyolefin film can be used as the heat seal layer 30. By using a polyethylene film as the heat seal layer 30, the laminate 1 can be made into a mono-material.

[0066] Examples of polyolefin resins that can be used for the heat seal layer 30 include ethylene resins such as low-density polyethylene resin (LDPE), medium-density polyethylene resin (MDPE), linear low-density polyethylene resin (LLDPE), ethylene-vinyl acetate copolymer (EVA), ethylene-α-olefin copolymer, and ethylene-(meth)acrylic acid copolymer, as well as blends of polyethylene and polybutene, and polypropylene resins such as homopolypropylene resin (PP), propylene-ethylene random copolymer, propylene-ethylene block copolymer, and propylene-α-olefin copolymer. These thermoplastic resins can be selected appropriately depending on the intended use and temperature conditions such as boiling treatment.

[0067] The heat seal layer 30 may contain various additives such as a flame retardant, a slip agent, an antiblocking agent, an antioxidant, a light stabilizer, and a tackifier. The thickness of the heat seal layer 30 can be appropriately set in consideration of the shape of the packaging bag to be manufactured, the mass of the contents to be contained, etc., and can be, for example, 30 to 150 μm.

[0068] When using a polyolefin film to produce a laminate 1 having an adhesive layer 20 and a heat seal layer 30, either a dry lamination method in which the films are bonded together using an adhesive such as a one-component curing or two-component curing urethane adhesive, or a non-solvent dry lamination method in which the films are bonded together using a solvent-free adhesive can be used. Alternatively, the heat seal layer 30 can be formed by extrusion lamination, in which a thermoplastic resin is heated and melted, extruded into a curtain shape, and laminated together. In this case, the adhesive layer 20 may be omitted.

[0069] The above is the basic structure of the laminate 1. In the laminate 1, the inorganic oxide layer 13 or the oxygen barrier film 14 is located between the substrate 11 and the heat seal layer 30. The gas barrier film 10 can be used alone for various packaging materials that require gas barrier properties, but by preparing one or more laminates in which the gas barrier film 10 is provided with a heat seal layer 30, and then placing the heat seal layers 30 opposite each other and heat-sealing the edges, various packaging materials such as packaging bags and standing pouches can be formed using the laminate 1.

[0070] The inventors have conducted various studies to find polyethylene substrates that have good adhesion to a heat seal layer, and have found that polyethylene substrates that have good adhesion can be identified by the probe descent temperature. The tip drop temperature is a parameter related to localized thermal analysis of materials using a probe and can be obtained by measuring the tip's rise and fall behavior. To measure the tip drop temperature, an atomic force microscope (AFM) equipped with a cantilever (probe) with a heating mechanism and a nanothermal microscope is used. The cantilever is placed in contact with the surface of a solid sample fixed to a sample stage. When a voltage is applied to the cantilever in contact mode to heat the sample, the sample surface thermally expands, causing the cantilever to rise. Further heating of the cantilever softens the sample surface, significantly changing its hardness. As a result, the cantilever descends and penetrates the sample surface. The point at which the sudden displacement detected at this point is the tip drop start point, and the voltage is converted into temperature to obtain the tip drop temperature. This method allows us to determine the tip drop temperature locally in the nanoscale region, near the surface.

[0071] Examples of AFMs that can be used include the MPF-3D-SA and Ztherm systems from Oxford Instruments, and the Nano Thermal Analysis series and nanoIR series from Bruker Japan. Measurements can also be performed on AFMs from other manufacturers by attaching a Nano Thermal Analysis. An example of a cantilever is the AN2-200 manufactured by Anasys Instruments, Inc. Other cantilevers can also be used as long as they can sufficiently reflect laser light and allow voltage to be applied.

[0072] The temperature range for the probe drop temperature measurement varies depending on the material to be measured, but for example, it can start from room temperature of about 25° C. and end at about 400° C. For the substrate 11 of this embodiment, it is preferable to measure in the range of 25° C. or higher and 300° C. or lower. The spring constant of the cantilever is preferably 0.1 to 3.5 N / m, and in order to perform measurements in both tapping mode and contact mode, it is preferable to use a cantilever with a spring constant of 0.5 to 3.5 N / m. In AFM, the deflection of the cantilever is often measured in voltage units, and in contact mode, the deflection of the cantilever changes before and after contact with the sample. By keeping this change within the range of 0.1 to 3.0 V, it is possible to keep the cantilever in contact with the sample while preventing damage to the sample surface.

[0073] The temperature rise rate of the cantilever varies depending on the heating mechanism, etc., but can be 0.1 V / sec or more and 10 V / sec or less, and preferably 0.2 V / sec or more and 5 V / sec or less. When the sample surface softens, the tip of the cantilever sinks into the sample and descends. The amount of cantilever sinking affects the detection sensitivity of the peak top of the softening curve and can be set to 3 to 500 nm. A sinking amount of 5 to 100 nm is more preferable because it prevents damage to the cantilever.

[0074] In order to calculate the probe drop temperature, it is necessary to create a calibration curve. In the examples described below, a calibration curve was created using four types of calibration samples: polycaprolactone, low-density polyethylene, polypropylene, and polyethylene terephthalate. Details of the creation of the calibration curve will be described later. The material of the calibration sample is not limited to the above, and it is sufficient to use a material whose thermal conductivity is not significantly different from that of a general polymer, and whose melting point is at least one of around 60°C, around 250°C, and somewhere in between. For example, the calibration sample can be made of any of the above four materials, excluding polypropylene.

[0075] The inventors' investigations have revealed that when the probe drop temperature is 180°C or less, sufficient adhesion strength between the substrate 11 and the heat seal layer 30 can be ensured, and when it is 165°C or less, this effect becomes even stronger. In this specification, "sufficient adhesion strength" means that the lamination strength between the substrate 11 and the heat seal layer 30 measured in accordance with JIS K6854 is 2N or more. As will be shown later using examples, in the laminate 1 according to this embodiment, sufficient adhesion strength between the substrate 11 and the heat seal layer 30 is ensured.

[0076] The probe drop temperature does not show a fixed relationship with the melting point or glass transition point, which are general parameters related to the softening of resins. The probe drop temperature shows a fixed correlation with the degree of molecular orientation of the resin film, and the value tends to be smaller for unstretched films. However, the inventors' investigations have shown that only a small number of biaxially stretched films have probe drop temperatures within the above range and exhibit sufficient adhesion strength with the heat seal layer. In other words, the probe drop temperature is a parameter independent of the general distinction between stretched and unstretched resin films, and the relationship with adhesion strength with the heat seal layer 30 was discovered for the first time by the inventors. When the substrate is made up of a plurality of layers made of different materials, it is sufficient that the probe drop temperature of the layer that constitutes the first surface is 180° C. or less.

[0077] An example of a procedure for producing the gas barrier film 10 and the laminate 1 will be described. First, a substrate 11 is selected that has a probe drop temperature of 180° C. or less. The substrate 11 may be a commercially available product or may be produced by a known method. The substrate 11 may be one in which a plurality of resin films are laminated together. In this case, a layer to be described later is formed on the surface of the resin film having a probe drop temperature of 180° C. or less as the first surface.

[0078] Next, on the substrate 11, an undercoat layer (if necessary) and one or both of the inorganic oxide layer 13 and the oxygen barrier film 14 are formed. When forming an undercoat layer, for example, a mixed liquid for forming the undercoat layer may be applied to the first surface 11a to form a coating film, and the coating film may be dried (to remove the solvent). The mixed solution can be applied by a known wet coating method, such as roll coating, gravure coating, reverse coating, die coating, screen printing, or spray coating. The coating film made from the mixed liquid can be dried by known drying methods such as hot air drying, hot roll drying, infrared irradiation, etc. The drying temperature for the coating film can be, for example, 50 to 200° C. The drying time varies depending on the thickness of the coating film, the drying temperature, etc., but can be, for example, 1 second to 5 minutes.

[0079] The inorganic oxide layer 13 can be formed by the above-mentioned vacuum deposition method, sputtering method, ion plating method, plasma vapor deposition (CVD) method, or the like. The oxygen barrier film 14 can be formed, for example, by applying a mixed liquid for forming the oxygen barrier film 14 to form a coating film, and then drying the coating film. The mixed solution can be applied and dried using the same methods as those described in the step of forming the undercoat layer 12. The oxygen barrier film 14 may be formed by a single application and drying, or by repeated application and drying of the same or different mixed liquids multiple times.

[0080] The laminate 1 may further be provided with a printed layer, a protective layer, a light-shielding layer, other functional layers, etc., as needed. The printed layer can be provided in a position visible from the outside of the laminate or packaging material in order to display information about the contents, identify the contents, or improve the design of the packaging bag. The printing method and printing ink are not particularly limited, and can be appropriately selected from known printing methods and printing inks in consideration of printability on the film, design such as color tone, adhesion, safety as a food container, etc. Examples of printing methods include gravure printing, offset printing, gravure offset printing, flexographic printing, and inkjet printing. Among these, gravure printing is preferred from the viewpoints of productivity and high definition of the image. To improve the adhesion of the printed layer, the surface of the layer on which the printed layer is formed may be subjected to various pretreatments such as corona treatment, plasma treatment, and flame treatment, or a coating layer such as an easy-adhesion layer may be provided. The printed layer can be provided between the inorganic oxide layer and the adhesive layer, between the oxygen barrier film and the adhesive layer, etc. Furthermore, as will be described later, when the substrate has a multi-layer structure, the printed layer can also be provided within the substrate.

[0081] The gas barrier film of this embodiment will be further described using examples and comparative examples, but the present invention is not limited to the specific contents of the examples and comparative examples.

[0082] The resin films used in the examples and comparative examples are shown below. α1: Unstretched polyethylene film (HD manufactured by Tamapoly Co., Ltd., thickness 40 μm, density 0.949 g / cm 3 , one side corona treated) α2: Unstretched polyethylene film (HS31 manufactured by Tamapoly Co., Ltd., thickness 30 μm, density 0.947 g / cm 3 , one side corona treated) α3: Unstretched polyethylene film (GAP manufactured by Charter NEX Films, Inc., thickness 25 μm, density 0.950 g / cm 3 , one side corona treated) α4: Unstretched polyethylene film (WINPAK Limited, thickness 25 μm, density 0.952 g / cm 3 , one side corona treated) α5: Unstretched polyethylene film (Poly Expert, Inc., thickness 25 μm, density 0.948 g / cm 3 , one side corona treated) α6: Uniaxially oriented polyethylene film (Tokyo Ink Co., Ltd., SMUQ, thickness 25 μm, density 0.950 g / cm 3 , one side corona treated) α7: Uniaxially oriented polyethylene film (Futamura Chemical Co., Ltd. PE3K-H, thickness 25 μm, density 0.950 g / cm 3 , one side corona treated) α8: Uniaxially oriented polyethylene film (PE3M manufactured by Futamura Chemical Co., Ltd., thickness 25 μm, density 0.950 g / cm 3 , one side corona treated) α9: Biaxially oriented polyethylene film (HD200 manufactured by Jindal Films, Inc., thickness 25 μm, density 0.950 g / cm 3 , one side corona treated)

[0083] The mixture used for layer formation was as follows: (Mixture for undercoat layer) Acrylic polyol, Acrydic CL-1000 manufactured by DIC Corporation, and TDI type curing agent, Coronate 2030 manufactured by Tosoh Corporation, were used as the acrylic polyol and the isocyanate compound, respectively, and the solids weight ratio of the acrylic polyol to the isocyanate compound was 6:4. Ethyl acetate was added to dilute the solids content to 2% by mass. In this way, a mixed solution for forming an undercoat layer was obtained.

[0084] (Mixture for organic-inorganic composite coating) Aqueous solutions of polyvinyl alcohol resin (Poval PVA-105 manufactured by Kuraray, saponification degree 98-99%, polymerization degree 500), tetraethoxysilane (TEOS), and γ-glycidoxypropyltrimethoxysilane (GPTMS, KBM-403 manufactured by Shin-Etsu Chemical Co., Ltd.) were prepared by hydrolyzing each solution with 0.02 mol / L hydrochloric acid. The three solutions were mixed so that the weight ratio of PVA:TEOS:GPTMS before hydrolysis was 40:50:10. The mixed solution was then diluted with a solvent so that the mass ratio of water to isopropyl alcohol in the solvent components was 90:10. As a result of the above, a mixed solution (5 mass %) for forming an organic-inorganic composite film was obtained.

[0085] (A coating mixture) 20 parts by mass of an aqueous solution of polyacrylic acid (Aron A-10H, manufactured by Toagosei Co., Ltd., solids concentration 25% by mass) with a number average molecular weight of 200,000 was diluted with 58.9 parts by mass of distilled water, followed by addition of 0.44 parts by mass of aminopropyltrimethoxysilane (APTMS, manufactured by Aldrich Chemical Co.), and stirring to obtain a uniform solution. As a result of the above, a mixed solution for coating A containing a polycarboxylic acid polymer as a main component was obtained.

[0086] (B film mixture) 100 parts by mass of zinc oxide fine particle aqueous dispersion (ZE143 manufactured by Sumitomo Osaka Cement Co., Ltd.) and 2 parts by mass of hardener (Liofol HAERTER UR 5889-21 manufactured by Henkel) were mixed to obtain a mixed solution for coating B containing a polyvalent metal compound as the main component.

[0087] The two types of adhesive used in the adhesive layer are shown below. (urethane adhesive) An adhesive made by mixing 100 parts by mass of Mitsui Chemicals' Takelac A525, 11 parts by mass of Mitsui Chemicals' Takenate A52, and 84 parts by mass of ethyl acetate. (gas barrier adhesive) An adhesive made by mixing 23 parts by mass of a solvent made by mixing ethyl acetate and methanol in a mass ratio of 1:1, with 16 parts by mass of Maxieve C93T manufactured by Mitsubishi Gas Chemical Company, Inc. and 5 parts by mass of Maxieve M-100 manufactured by Mitsubishi Gas Chemical Company, Inc.

[0088] (Examples 1 to 5, 11 to 12, and Comparative Examples 1 to 4) The mixed solution for the undercoat layer was applied to the corona-treated surface of any of the resin films α1 to α9 using a gravure printing machine to form a coating film, and the coating film was then passed through a 60°C oven for 10 seconds to dry, forming an undercoat layer with a thickness of 0.1 μm. Next, a 30 nm thick inorganic oxide layer made of silicon oxide was formed on the undercoat layer using a vacuum deposition apparatus using an electron beam heating method and a mixed material containing two or more of metallic silicon, silicon monoxide, and silicon dioxide. The mixed solution for the organic-inorganic composite coating was applied onto the inorganic oxide layer using a gravure printing machine to form a coating film, and the coating film was dried by passing it through an oven at 60°C for 10 seconds to form an oxygen barrier coating made of an organic-inorganic composite coating having a thickness of 0.3 μm, thereby obtaining the gas barrier films according to Examples 1 to 5, 11 to 12, and Comparative Examples 1 to 4. The resin films used in each example are shown in Table 1.

[0089] Example 6 A gas barrier film according to Example 6 was obtained in the same manner as in Example 3, except that no undercoat layer was provided.

[0090] (Examples 7 to 9 and Comparative Examples 5 to 6) The mixed solution for the undercoat layer was applied to the corona-treated surface of any of the resin films α1 to α9 using a gravure printing machine to form a coating film, and the coating film was then passed through a 60°C oven for 10 seconds to dry, forming an undercoat layer with a thickness of 0.1 μm. Next, deposition was carried out using an electron beam heating vacuum deposition apparatus and metallic aluminum under the introduction of oxygen gas to form an inorganic oxide layer of aluminum oxide having a thickness of 20 nm on the undercoat layer. A coating A mixture was applied to the inorganic oxide layer using a gravure printer to form a coating, and the coating was then dried in a 60°C oven for 10 seconds to form a 0.2µm thick coating A. A coating B mixture was then applied to the inorganic oxide layer using a gravure printer to form a coating, and the coating was then dried in a 60°C oven for 10 seconds to form a 0.2µm thick coating B. This resulted in the formation of an oxygen barrier coating made of a polyvalent metal salt of polycarboxylic acid, and the gas barrier films of Examples 7 to 9 and Comparative Examples 5 and 6 were obtained. The resin films used in each example are shown in Table 1.

[0091] Example 10 The mixed solution for the undercoat layer was applied to the corona-treated surface of resin film α4 using a gravure printing machine to form a coating film, and the coating film was then dried in a 60°C oven for 10 seconds to form an undercoat layer with a thickness of 0.1 μm. Next, a coating A mixture was applied using a gravure printing machine to form a coating, and the coating was dried in an oven at 60°C for 10 seconds to form a 0.2 μm thick coating A. Further, a coating B mixture was applied using a gravure printing machine to form a coating, and the coating was dried in an oven at 60°C for 10 seconds to form a 0.2 μm thick coating B. In this way, an oxygen barrier coating made of a polyvalent metal salt of polycarboxylic acid was formed, and the gas barrier film of Example 10 was obtained.

[0092] (Examples 13 to 15 and Comparative Examples 7 and 8) Gas barrier films according to Examples 13 to 15 and Comparative Examples 7 and 8 were obtained in the same manner as in Example 1, etc., except that no oxygen barrier film was formed. The resin films used in each example are shown in Table 1.

[0093] Example 16 A gas barrier film according to Example 16 was obtained in the same manner as in Example 8, except that no oxygen barrier coating was formed.

[0094] The gas barrier films of the examples and comparative examples were evaluated for the following items. (Measurement of probe drop temperature of substrate) Before producing the gas barrier film, the probe drop temperature of each resin film was measured in the following manner. The atomic force microscope used was an Oxford Instruments MPF-3D-SA, and the nanothermal microscope used was an Oxford Instruments Ztherm. The cantilever used was an Anasys Instruments AN2-200. After measuring the shape of the sample with a 10 μm field of view in AC mode, the cantilever was separated from the sample by 5 to 10 μm in the Z direction (normal to the sample surface). In this state, the detrend correction function of the instrument was performed in contact mode under conditions of a maximum applied voltage of 6 V and a heating rate of 0.5 V / s to correct for changes in the cantilever deflection due to the applied voltage. The cantilever was then brought into contact with the sample in contact mode so that the change in deflection between the cantilever and the sample was 0.2 V. While maintaining a constant deflection, the sample was heated by applying a voltage of 6 V maximum and a heating rate of 0.5 V / s to the cantilever. The cantilever's Z-direction displacement was recorded, and the measurement was stopped when the Z-displacement changed from rising to falling and fell 50 nm from the point of change. If the Z-displacement reached the maximum applied voltage without falling 50 nm from the point of change, the maximum applied voltage during detrend correction and measurement was increased by 0.5 V and the measurement was repeated. The applied voltage at which the recorded Z-displacement reached its maximum was converted to temperature. This measurement was performed at 10 points within a 10 μm field of view, and the average of the 10 points was taken as the tip drop temperature. A calibration curve was used to convert the applied voltage to temperature. Polycaprolactone (melting point 60°C), low-density polyethylene (112°C), polypropylene (166°C), and polyethylene terephthalate (255°C) were measured as calibration samples, and calibration curves for applied voltage and temperature were constructed. The melting point was the peak melting temperature measured by differential scanning calorimetry (DSC) at a heating rate of 5°C / min. The calibration sample measurement method was the same as for the sample measurements, except that the maximum applied voltage during detrend correction and measurement was 3.5 V for polycaprolactone, 5.5 V for low-density polyethylene, 6.5 V for polypropylene, and 7.8 V for polyethylene terephthalate. The relationship between the applied voltage at which the Z displacement was maximized during measurement of each calibration sample and the melting point was approximated by a cubic function using the least-squares method. The calibration curves were then constructed.

[0095] (Production of packaging materials) An LLDPE film (TUX MC-S, manufactured by Mitsui Chemicals Tocello, Inc., thickness 60 μm) that would serve as a heat seal layer was dry laminated onto the inorganic oxide layer or oxygen barrier coating surface of each gas barrier film using an adhesive. This was then cured at 40°C for 3 days to produce a laminate according to each example. The adhesive used was one of the following: Urethane adhesive: Mitsui Chemicals Polyurethanes Takelac A525 / Takenate A52 Gas barrier adhesive: Mitsubishi Gas Chemical Company, Inc., Maxive C93T / M-100 A5 size sealed pouches were prepared using the laminates of each example, and 150 ml of tap water was filled in and sealed. In this manner, packaging materials according to the respective examples were obtained.

[0096] The packaging material according to each example was subjected to a boiling treatment for 30 minutes in hot water at 90° C. Before and after the boiling treatment, the oxygen permeability and the lamination strength between the substrate and the heat seal layer were measured. (oxygen permeability) The laminate before and after the boiling treatment was measured for oxygen permeability under conditions of 30° C. and 70% RH (relative humidity) using an oxygen permeability measuring device (OXTRAN-2 / 20 manufactured by MOCON). (Lamination strength between substrate and heat seal layer) In accordance with JIS Z1707, 15 mm wide rectangular test pieces were cut out from the laminates of each example, and the lamination strength between the substrate and the heat seal layer was measured using an Orientec Tensilon universal testing machine RTC-1250 under the following four conditions. 180° peeling normal state (Dry 180°) T-type peeling normal (DryT) 180° peeling, wet measurement area (Wet180°) T-type peeling, wet measurement site (WetT) The results are shown in Tables 1 and 2.

[0097] [Table 1]

[0098] [Table 2]

[0099] In all of the Examples and Comparative Examples, the polyethylene content was 90% by mass or more in both the gas barrier film and the laminate, and the recyclability was good. In all of the Examples, the probe drop temperature on the first surface of the substrate was 180°C or less, and the laminate strength between the substrate and the heat-seal layer was sufficient both before and after boiling, regardless of the layer configuration between the substrate and the heat-seal layer. The oxygen permeability varied slightly depending on the layer configuration between the substrate and the heat-seal layer and the adhesive layer, but it was confirmed that the oxygen barrier properties were maintained without any problems even after boiling. On the other hand, the gas barrier films of the comparative examples had no problems with oxygen barrier properties, but the probe drop temperatures of the substrates were all 180°C or higher, and the laminate strength between the substrate and the heat seal layer was less than 2N / 15mm even before boiling, which was insufficient. The laminate strength tended to decrease further after boiling. From the above, it was shown that in gas barrier films and laminates using polyethylene, by setting the probe drop temperature of the substrate to 180°C or less, it is possible to achieve both good recyclability through mono-materialization and sufficient adhesive strength between the substrate and the heat seal layer.

[0100] The above describes one embodiment of the present invention and examples, but the specific configuration is not limited to this embodiment, and includes modifications and combinations of configurations within the scope that does not deviate from the gist of the present invention. [Industrial Applicability]

[0101] The laminate of the present invention exhibits excellent oxygen barrier properties and sufficient adhesive strength between the substrate and the heat seal layer, and since the polyethylene content is 90% by mass or more, it is highly recyclable as a polyethylene material. The laminate of the present invention can be suitably used as a variety of packaging materials, and is particularly suitable as a packaging material that is subjected to a boiling treatment, and is capable of maintaining the quality of the contents for a long period of time.

[0102] The gas barrier film of the present invention exhibits excellent oxygen barrier properties and exhibits sufficient adhesive strength when bonded to a heat seal layer. The laminate and gas barrier film of the present invention can also be used for applications other than packaging materials, such as electronic device-related films, solar cell films, various functional films for fuel cells, and substrate films. [Explanation of symbols]

[0103] 1. Laminate 10 Gas barrier film 11 Base material 11a Front page 13 Inorganic oxide layer 14 Oxygen barrier coating 20 Adhesive layer 30 Heat seal layer

Claims

1. an unstretched film containing polyethylene; an inorganic oxide layer formed on the first surface side of the unstretched film; Equipped with the first surface of the unstretched film is made of polyethylene; a probe drop temperature on the first surface side of the unstretched film is 150°C or higher and 180°C or lower; The proportion of the polyethylene in the whole is 90 mass% or more, does not include a layer containing water-swellable mica; Gas barrier film.

2. The density of the polyethylene is 0.94 g / cm ３ That's all. The gas barrier film according to claim 1 .

3. The gas barrier film according to claim 1 or 2; a heat seal layer containing polyethylene and joined to the gas barrier film so as to sandwich the inorganic oxide layer between the unstretched film and the heat seal layer; Equipped with The proportion of the polyethylene in the whole is 90 mass% or more, Laminate.

4. the gas barrier film and the heat seal layer are bonded together by an adhesive layer; The laminate according to claim 3 .

5. The adhesive layer is made of a gas barrier adhesive. The laminate according to claim 4.

6. A packaging material formed using the laminate according to any one of claims 3 to 5.

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