Thin Air Barrier Sheets and Methods for Producing Thin Air Barrier Sheets

Abstract

The invention relates to a thin, gas-blocking film capable of exhibiting superior gas-blocking and aroma retention properties under high temperature and high humidity conditions, even after vacuum packaging, despite being a thinner film. The invention proposes a gas barrier thin film of total thickness of 100 μm or less, consisting of a plastic matrix (I) and a gas barrier layer (II) laminated onto a plastic matrix, the gas barrier thin film is characterized by (1) the plastic matrix (I) consisting of a metal-containing layer comprising a resin component and at least one of the metals and metal compounds, (2) the total content of metals and metal compounds in the metal-containing layer is between 0.1 and 20% by mass, (3) the gas barrier layer (II) containing a polycarboxylic acid, (4) the metal-containing layer and the gas barrier layer being laminated so that they are in direct contact with each other, and (5) the combined elastic modulus of the surface of the gas barrier layer (II) measured by nano-hardness measurement when the thin film is sterilized at 120°C for 30 minutes is between 9.0 and 12.5 GPa.

Description

Gas barrier laminate and method for producing the same

[0001] The present invention relates to a gas barrier laminate and a method for producing the same.

[0002] Plastic films such as polyamide films are widely used as packaging materials due to their excellent strength, transparency, formability, etc. However, these plastic films have high permeability to gases such as oxygen, so when used to package general foods, retort-processed foods, cosmetics, medical supplies, pesticides, etc., the contents may come into contact with the permeated oxygen and oxidize, causing discoloration and a deterioration in taste.

[0003] For this reason, plastic films used for these packaging applications are required to have oxygen barrier properties, and in the case of packaging foods and the like that contain moisture, gas barrier properties are also required under high humidity conditions.

[0004] As a method for imparting oxygen barrier properties to a plastic film, a method of laminating a gas barrier layer on the film has been proposed. Specifically, it is known to use a gas barrier layer composed of a polycarboxylic acid polymer, a polyalcohol polymer, and a metal compound. For example, Patent Document 1 proposes a gas barrier laminate having excellent oxygen barrier properties in a high-humidity environment close to room temperature.

[0005] JP 2017-185652 A JP 2007-276421 A International Publication WO2014 / 042133 JP 2019-151025 A

[0006] However, although the gas barrier laminate disclosed in Patent Document 1 and the like has excellent gas barrier properties at around room temperature, there is still room for improvement in gas barrier performance under high temperature and high humidity environments.

[0007] In recent years, as global warming progresses, the surrounding environment during cargo transport in the summer has become extremely hot and humid. From the perspective of suppressing oxidative deterioration of the contents, there is a strong demand for materials that can exhibit excellent gas barrier properties even in high-temperature, high-humidity environments, and there is increasing importance being placed on the ability to exhibit gas barrier properties in high-temperature, high-humidity environments of 40°C or higher in particular.

[0008] In particular, when the packaging material is used for vacuum packaging, there are still some points that need to be improved, such as gas barrier properties under high temperature and high humidity conditions in a state where local stretching or bending / bending occurs.

[0009] For example, as shown in Figure 3A, when a vacuum-packed product is produced by sealing food 31 (including processed foods) with packaging material 32, before vacuuming, packaging material 32 is placed in contact with part of the surface of food 31. In contrast, as shown in Figure 3B, vacuuming causes packaging material 32 to adhere closely to the unevenness of the surface of food 31. In this case, for example, in region A in Figure 3B, the packaging material conforms to the concave shape of the food surface, causing the packaging material to bend and flex locally. Also, for example, in region B in Figure 3B, the packaging material conforms to the convex shape of the food surface, causing the packaging material to be stretched locally.

[0010] In this way, the packaging material is locally bent, flexed, or locally stretched to conform to the shape of the surface of the contents, and these bent, flexed, or stretched portions are likely to develop fine cracks or to develop fine cracks over time. From this perspective, there is a need for the development of a packaging material that is durable against localized bending, flexing, and stretching.

[0011] Furthermore, packaging materials are required to prevent the leakage of odor components (aroma or odor) from the contents, even in high-temperature and high-humidity environments. In high-temperature and high-humidity environments, the vapor pressure of odor components increases, making them more likely to leak to the outside. Once odor components from the contents leak, not only will the scent of the contents be lost or diminished, but the odor may also transfer to other packaging materials, other products, etc. Therefore, packaging materials are also required to have the ability to block odor components (aroma retention).

[0012] Generally, increasing the thickness of the gas barrier film is considered as a method for improving the gas barrier properties. However, there is a demand for the development of thinner films, particularly from the viewpoints of the film's bag-forming properties and the weight reduction of film products, as well as from the viewpoint of reducing the volume of raw materials in light of recent environmental concerns.

[0013] Thus, there is a strong demand for the development of a material that can exhibit high gas barrier properties and the like in high-temperature and high-humidity environments, even though it is a thinner film (particularly a film with a total thickness of 100 μm or less). However, at present, such a material has not yet been developed.

[0014] Therefore, a main object of the present invention is to provide a gas barrier laminate that is a thinner film but can still exhibit excellent gas barrier properties and aroma retention properties in a high-temperature, high-humidity environment even after vacuum packaging.

[0015] The present inventors have conducted extensive research in light of these problems in the prior art, and as a result have found that a film obtained by a specific manufacturing method can achieve the above object, thereby completing the present invention.

[0016] That is, the present invention relates to the following gas barrier laminate and its manufacturing method: 1. A laminate having a total thickness of 100 μm or less, comprising a plastic substrate (I) and a gas barrier layer (II) laminated on the plastic substrate, wherein: (1) the plastic substrate (I) comprises a metal-containing layer containing at least one of a metal and a metal compound and a resin component; (2) the total content of the metal and metal compound in the metal-containing layer is 0.1 to 20 mass %; (3) the gas barrier layer (II) contains a polycarboxylic acid; (4) the metal-containing layer and the gas barrier layer are laminated so as to be in direct contact with each other; and (5) the composite elastic modulus of the surface of the gas barrier layer (II) after retorting the laminate at 120°C for 30 minutes is 9.0 to 12.5 GPa when measured by nanoindentation. 3. The gas barrier laminate according to Item 1, wherein the surface of the gas barrier layer (II) of the laminate is subjected to a retort treatment at 120°C for 30 minutes, and the surface has a hardness of 0.7 to 1.3 GPa when measured by nanoindentation. 4. The gas barrier laminate is subjected to a retort treatment at 120°C for 30 minutes, and is stretched by 7% simultaneously in both the MD and TD directions at a rate of 1.5% / s in an environment of a temperature of 35°C and a humidity of 50% RH, and then has an oxygen permeability of 100 ml / (m) in an environment of 40°C and 90% RH. ２Item 3. The gas barrier laminate according to any one of items 1 to 2, wherein the plastic substrate (I) is constituted by a multilayer film including a metal-containing layer. 5. The gas barrier laminate according to any one of items 1 to 4, wherein the gas barrier layer (II) further contains a polyalcohol. 6. The gas barrier laminate according to any one of items 1 to 5, wherein the gas barrier layer (II) has a thickness of 0.05 to 5.00 μm and the plastic substrate (I) has a thickness of 5 to 99.95 μm. 7. The gas barrier laminate according to any one of items 1 to 6, wherein the polycarboxylic acid comprises at least one of polyacrylic acid, an acrylic acid-maleic acid copolymer, and an olefin-maleic acid copolymer. 8. 8. The gas barrier laminate according to any one of items 1 to 7, wherein the resin component contained in the metal-containing layer comprises one or more thermoplastic resins, and the content of the resin component in the metal-containing layer is 99.9 to 80% by mass. 9. The gas barrier laminate according to any one of items 1 to 8, wherein the plastic substrate (I) is composed of one or more metal-containing layers and one or more other resin-containing layers, and the ratio [(Rt) / (Mt)] of the total thickness (Mt) of the metal-containing layers (M) to the total thickness (Rt) of the other resin-containing layers (R) is 1 / 10 to 10 / 1. 10. The gas barrier laminate according to any one of items 1 to 9, wherein the metal compound is at least one of lithium carbonate, sodium bicarbonate, magnesium oxide, magnesium carbonate, magnesium hydroxide, magnesium acetate, calcium oxide, calcium carbonate, calcium hydroxide, calcium chloride, calcium phosphate, calcium sulfate, calcium acetate, zinc acetate, zinc oxide, and zinc carbonate. 11. 11. The gas barrier laminate according to any one of items 1 to 10, wherein the gas barrier layer (II) comprises an olefin-maleic acid copolymer, and the content of maleic acid units in the olefin-maleic acid copolymer is 5 mol% or more. 12. The gas barrier laminate according to any one of items 1 to 11, wherein the metal and metal compound are in the form of powder, with an average particle size of 0.005 to 5.0 μm. 13. A packaging bag comprising the gas barrier laminate according to any one of items 1 to 12.14. A vacuum-packed product in which at least a solid material is contained and sealed in the packaging bag according to Item 13. 15. A method for producing a gas barrier laminate, comprising: (1) preparing a raw material liquid containing polycarboxylic acid, mineral oil, and an acetylene glycol-based nonionic surfactant, wherein the mass ratio of the mineral oil to the acetylene glycol-based nonionic surfactant is 80 / 20 to 40 / 60, and (2) applying the raw material liquid as a coating liquid for forming a gas barrier layer (II) onto at least the surface of a metal-containing layer of a plastic substrate (I) including the metal-containing layer containing at least one of a metal and a metal compound and a resin component. 16. The production method according to Item 15, further comprising the step of passing the raw material liquid through a filter with a filtration accuracy of 1.0 to 10.0 μm to prepare a coating liquid for forming a gas barrier layer (II) prior to coating the raw material liquid on the plastic substrate (I). 17. 17. The method for producing a gas barrier laminate according to any one of items 15 to 16, further comprising a step of applying the raw material liquid to a plastic substrate (I) and then subjecting the laminate coated with the raw material liquid to simultaneous biaxial stretching or sequential biaxial stretching.

[0017] According to the present invention, it is possible to provide a gas barrier laminate that is a thinner film but is still able to exhibit excellent gas barrier properties and aroma retention properties even after vacuum packaging in a high-temperature, high-humidity environment.

[0018] In particular, the present invention employs a production method that uses a coating liquid containing a fixed ratio of mineral oil and an acetylene glycol-based nonionic surfactant (particularly a coating liquid containing a pre-dispersion in which mineral oil is thoroughly dispersed), thereby enabling the formation of a unique gas barrier layer whose surface has a relatively uniform, consistent composite modulus of elasticity (hereinafter simply referred to as "modulus of elasticity"). Such a unique gas barrier layer can more reliably provide a gas barrier laminate that exhibits excellent gas barrier properties and aroma retention under harsh conditions of high temperature and high humidity, even after being subjected to bending or deflection due to stretching or wrinkling that occurs during vacuum packaging.

[0019] As described above, the gas barrier laminate of the present invention is suitable for food applications where permeability to oxygen and other gases is undesirable. In particular, it can exhibit excellent gas barrier properties and aroma retention in high-temperature, high-humidity environments even after bending or flexing due to stretching or wrinkling that occurs during vacuum packaging. This makes it possible to ensure longer shelf lives and use-by dates, and ultimately enables product transportation over long periods of time and long distances.

[0020] 1 is a diagram showing an example of a layer structure of the gas barrier laminate of the present invention, and FIG. 2 is a diagram showing another example of a layer structure of the gas barrier laminate of the present invention, and FIG. 3 is a schematic diagram showing the state of the surface of the content and the packaging material when a vacuum-packed product is produced by sealing the content with the packaging material.

[0021] 1. Gas Barrier Laminate The gas barrier laminate of the present invention (laminate of the present invention) is a laminate comprising a plastic substrate (I) and a gas barrier layer (II) laminated on the plastic substrate, and having a total thickness of 100 μm or less, characterized in that: (1) the plastic substrate (I) comprises a metal-containing layer containing at least one of a metal and a metal compound and a resin component; (2) the total content of the metal and metal compound in the metal-containing layer is 0.1 to 20 mass %; (3) the gas barrier layer (II) contains a polycarboxylic acid; (4) the metal-containing layer and the gas barrier layer are laminated so as to be in direct contact with each other; and (5) the composite modulus of elasticity of the surface of the gas barrier layer (II) after retorting the laminate at 120°C for 30 minutes is 9.0 to 12.5 GPa when measured by a nanoindentation method.

[0022] An example of the layer structure of a laminate of the present invention is shown in Figure 1. In the laminate 10 of Figure 1A, a plastic substrate 11 is composed of a single layer of a metal-containing layer 11a containing a metal or metal compound (hereinafter, unless otherwise specified, both will be collectively referred to as "metal component"), and a gas barrier layer 12 is laminated on the surface of the metal-containing layer 11a. Direct contact between the metal-containing layer 11a and the gas barrier layer 12 causes a reaction between the metal component contained in the metal-containing layer 11a and the polycarboxylic acid contained in the gas barrier layer 12, thereby achieving better gas barrier properties. The reason why the gas barrier properties are enhanced by this reaction is thought to be that the metal component (metal ion) in the metal-containing layer (particularly in the coating film of the gas barrier layer-forming coating liquid described below) migrates to the gas barrier layer, and the carboxyl groups of the polycarboxylic acid react with the metal component in the gas barrier layer, forming a certain amount of crosslinked structures between the polycarboxylic acid molecules.

[0023] In the laminate 10' of Figure 1B, the plastic substrate 11 is composed of a multilayer structure including a metal-containing layer 11a containing a resin component and a metal component, and resin-containing layers 11b and 11c not containing a metal component (hereinafter also referred to as "other resin-containing layers"), with a gas barrier layer 12 laminated on the surface of the metal-containing layer 11a. In this case, too, direct contact between the metal-containing layer 11a and the gas barrier layer 12 causes a reaction between the metal component contained in the metal-containing layer 11a and the polycarboxylic acid contained in the gas barrier layer 12, thereby achieving superior gas barrier properties. While two other resin layers are shown in Figure 1B, one or more other resin layers may be used.

[0024] 1C , the plastic substrate 11 is composed of a single layer of a metal-containing layer 11a containing a metal component, and gas barrier layers 12, 12 are laminated on both surfaces of the metal-containing layer 11a. In this case as well, the metal-containing layer 11a and the gas barrier layers 12, 12 come into direct contact with each other, causing a reaction between the metal component contained in the metal-containing layer 11a and the polycarboxylic acid contained in the gas barrier layers 12, 12, thereby enabling the exhibiting of more excellent gas barrier properties.

[0025] 1A and 1B show only one metal-containing layer, but two or more layers may be formed. As shown in FIG. 2, the plastic substrate 11 may be composed of multiple layers in which metal-containing layers 11a, 11a containing a metal component are laminated on both sides of another resin-containing layer 11b, and a gas barrier layer 12, 12 is laminated on the surface of each metal-containing layer 11a, 11a. In other words, a layer structure in which another resin-containing layer 11b is sandwiched between two metal-containing layers 11a, 11a is also included in the present invention. In this way, a gas barrier layer (II) is laminated on at least one side of the plastic substrate (I), while a gas barrier layer (II) or another barrier layer may also be provided on the opposite side. In this way, by forming a double-sided coating with two metal-containing layers 11a, 11a, it is possible to further improve the gas barrier property in high-temperature and high-humidity environments. Note that a laminate having three or more metal-containing layers is also included in the present invention.

[0026] Each layer constituting the gas barrier laminate of the present invention will be specifically described below.

[0027] (1) Regarding Each Layer (1-1) Plastic Substrate The plastic substrate not only functions as a supporting member for the laminate of the present invention, but also serves as a source for supplying metal components to the gas barrier layer.

[0028] The plastic substrate includes a metal-containing layer (a layer containing a metal element) containing at least one of a metal and a metal compound and a resin component. Therefore, the plastic substrate may be a single layer consisting of one metal-containing layer, or may be a multi-layer including a metal-containing layer and another layer. Furthermore, the plastic substrate may have two or more metal-containing layers.

[0029] The at least one metal and metal compound may be any metal that can supply metal ions to the gas barrier layer to form the crosslinked structure described above. More specifically, the following metals or metal compounds can be used:

[0030] The metal (single metal) is not limited, but from the viewpoint of gas barrier properties, preferred are, for example, monovalent metals such as lithium, sodium, potassium, rubidium, and cesium, and divalent or higher metals such as magnesium, calcium, zirconium, zinc, copper, cobalt, iron, nickel, and aluminum. Among these, metals with a high ionization tendency are preferred from the viewpoint of ease of reaction with carboxylic acid. Specifically, at least one of lithium, sodium, potassium, magnesium, calcium, and zinc is preferred, and at least one of magnesium, calcium, and zinc is particularly preferred.

[0031] The metal constituting the metal compound is not particularly limited, but monovalent metals such as lithium, sodium, potassium, rubidium, and cesium, and divalent or higher metals such as magnesium, calcium, zirconium, zinc, copper, cobalt, iron, nickel, and aluminum are preferred from the viewpoint of gas barrier properties. The type of metal is not limited to one type, and two or more types may be used. Among these, metals with a high ionization tendency are preferred from the viewpoint of ease of reaction with carboxylic acid. Specifically, at least one of lithium, sodium, potassium, magnesium, calcium, and zinc is preferred, and at least one of magnesium, calcium, and zinc is particularly more preferred.

[0032] The metal compound may be any compound containing the above metals, and examples thereof include inorganic salts such as oxides, hydroxides, halides, carbonates, hydrogencarbonates, phosphates, and sulfates, carboxylates such as acetates, formates, stearates, citrates, malates, and maleates, and organic acid salts such as sulfonates. These may be used alone or in combination of two or more.

[0033] Specific examples of the metal compound that can be suitably used include at least one of lithium carbonate, sodium hydrogencarbonate, magnesium oxide, magnesium carbonate, magnesium hydroxide, magnesium acetate, calcium oxide, calcium carbonate, calcium hydroxide, calcium chloride, calcium phosphate, calcium sulfate, calcium acetate, zinc acetate, zinc oxide, zinc carbonate, etc. In the present invention, at least one of oxides, hydroxides, carbonates, hydrogencarbonates, acetates, etc. is preferred.

[0034] In particular, from the viewpoint of gas barrier properties, preferred are divalent metal compounds such as magnesium salts such as magnesium oxide, magnesium carbonate, magnesium hydroxide, and magnesium acetate; calcium compounds such as calcium carbonate and calcium acetate; and zinc compounds such as zinc oxide and zinc acetate.

[0035] In particular, from the viewpoint of ensuring the transparency of the plastic substrate (I), monovalent metal compounds such as lithium carbonate and sodium bicarbonate, and divalent metal compounds (particularly magnesium compounds) such as magnesium oxide, magnesium carbonate and magnesium hydroxide are preferred. These can be used alone or in combination of two or more. Among these, at least one of an oxide and a carbonate is particularly preferred.

[0036] In a preferred embodiment of the present invention, at least one magnesium compound can be suitably used as the metal component. More specifically, at least one of magnesium oxide, magnesium hydroxide, and magnesium carbonate can be suitably used.

[0037] The form of the metal component is not particularly limited, but is usually preferably powder-like. In this case, the average particle size is not particularly limited, but is usually within the range of about 0.001 to 10.0 μm, more preferably 0.005 to 5.0 μm, even more preferably 0.01 to 2.0 μm, and most preferably 0.05 to 1.0 μm. In terms of improving the transparency of the plastic substrate (I), a smaller average particle size of the metal component is preferable. On the other hand, metal components with an average particle size of less than 0.001 μm tend to aggregate due to their large surface area, and coarse aggregates may be scattered throughout the film, reducing the mechanical properties of the substrate. On the other hand, plastic substrates (I) containing metal components with an average particle size exceeding 10.0 μm tend to break more frequently during film formation, resulting in reduced productivity. In addition, an average particle size exceeding 10.0 μm may be unsuitable when the thickness of the plastic substrate (I) is thin.

[0038] The metal component particles can be subjected to a surface treatment such as an inorganic treatment or an organic treatment to improve or enhance dispersibility, weather resistance, wettability with thermoplastic resins, heat resistance, transparency, etc. Examples of inorganic treatments include alumina treatment, silica treatment, titania treatment, zirconia treatment, tin oxide treatment, antimony oxide treatment, zinc oxide treatment, etc. Examples of organic treatments include treatments using fatty acid compounds, polyol compounds such as pentaerythritol and trimethylolpropane, amine compounds such as triethanolamine and trimethylolamine, silicone resins, and silicone compounds such as alkylchlorosilanes.

[0039] The content of metal components in the metal-containing layer (total content of simple metal and metal compound) is typically 0.1 to 20% by mass, preferably 0.2 to 10% by mass, more preferably 0.3 to 5% by mass, even more preferably 0.3 to 3% by mass, and most preferably 0.3 to 1% by mass. When the content of metal compounds in the metal-containing layer is 0.1 to 20% by mass, the resulting gas barrier laminate can exhibit excellent gas barrier properties and aroma retention. When the content of metal compounds is less than 0.1% by mass, the crosslinked structure formed by reaction with the polycarboxylic acid in the gas barrier layer (II) is reduced, resulting in a decrease in the gas barrier properties of the resulting gas barrier laminate, or the hardness of the gas barrier layer (II) may fall below the preferred range, resulting in a decrease in barrier properties after bending. On the other hand, when the content of the plastic substrate (I) exceeds 20% by mass, the plastic substrate (I) frequently breaks during stretching during film formation, which tends to reduce productivity. Furthermore, the mechanical properties and transparency also tend to decrease, and the hardness of the gas barrier layer (II) may exceed the preferred range, resulting in a decrease in the barrier properties after bending.

[0040] The method for incorporating a metal component into the metal-containing layer is not particularly limited, and the metal component can be incorporated at any time during the manufacturing process. Examples include a) a method in which the metal component is added when polymerizing the thermoplastic resin that constitutes the metal-containing layer, b) a method in which the thermoplastic resin and the metal component are kneaded together in an extruder, and c) a method in which a masterbatch containing a high concentration of the metal component is manufactured and then the resulting masterbatch is added to a thermoplastic resin for dilution (masterbatch method). In the present invention, the masterbatch method is preferably employed from the viewpoint of work efficiency.

[0041] In the present invention, the resin component constituting the metal-containing layer is not particularly limited, but usually one or more thermoplastic resins can be used.

[0042] Examples of thermoplastic resins include polyolefin resins such as polyethylene, polypropylene, and ionomer; polyamide resins such as nylon 6, nylon 66, nylon 46, nylon MXD6 (polymethaxylylene adipamide), and nylon 9T; polyester resins such as polyethylene terephthalate, polyethylene isophthalate, polyethylene naphthalate, polytrimethylene terephthalate, polytrimethylene naphthalate, polybutylene terephthalate, polybutylene naphthalate, and polylactic acid; vinyl chloride, polystyrene resin, polycarbonate resin, polyarylate resin, ethylene-vinyl acetate copolymer, and ethylene-vinyl alcohol copolymer. Among these thermoplastic resins, at least one of polyamide resin and polyester resin is preferred. In particular, polyamide resin (particularly nylon 6) is more preferred in terms of excellent puncture strength and impact resistance when used to form packaging bags. Furthermore, polyester resin (polyethylene terephthalate) is more preferred in terms of excellent heat resistance and economy. Therefore, these resin components can be appropriately selected depending on the application of the laminate of the present invention.

[0043] The thermoplastic resin constituting the metal-containing layer may contain any of the following components, or a combination of these components: a chemically recycled resin component polymerized using recycled monomers or recycled oligomers obtained by depolymerizing biomass-derived components, waste resin materials, etc. as starting materials; and a material recycled resin component obtained by crushing edge trimming scraps, slit scraps, etc. generated during film production, and melting and pelletizing the waste scraps or defective film again.

[0044] The content of the resin component in the metal-containing layer is usually the remainder excluding the metal component and any additives added as needed, and can be set, for example, from 99.9 to 80 mass %, or from 99.8 to 100 mass %, or from 99.7 to 95 mass %, or even from 99.7 to 99 mass %.

[0045] The metal-containing layer may contain, as necessary, at least one of various additives such as heat stabilizers, antioxidants, reinforcing materials, pigments, antidegradants, weathering agents, flame retardants, plasticizers, preservatives, UV absorbers, antistatic agents, antiblocking agents, etc., within a range that does not impair the effects of the present invention and does not adversely affect the performance of the plastic substrate (I). Furthermore, for the purpose of improving the slip properties of the plastic substrate (I), an inorganic or organic lubricant other than the metal component may be added to the metal-containing layer, and the addition of silica is particularly preferred.

[0046] The total content of these additives is usually about 5 mass % or less in the metal-containing layer, but is not limited to this. If these additives also fall under the category of "at least one of a metal and a metal compound" in the metal-containing layer, the content of the additive is counted as the content of the "at least one of a metal and a metal compound."

[0047] The thickness of the metal-containing layer (single layer) is not limited, but from the standpoint of thickness control, reactivity with the gas barrier layer, etc., it is usually sufficient to set it within a range of about 5 to 100 μm, and particularly preferably 10 to 30 μm.

[0048] As described above, the plastic substrate (I) may be composed of a single metal-containing layer, or may be composed of a multilayer structure including a metal-containing layer and one or more other resin-containing layers.

[0049] In this case, the other resin-containing layer may be a layer containing a thermoplastic resin. The thermoplastic resin may be at least one of the thermoplastic resins that can be used in the metal-containing layer. In this case, the thermoplastic resin contained in the metal-containing layer and the thermoplastic resin contained in the other resin-containing layer may be the same or different.

[0050] The other resin-containing layer may also contain at least one of the additives that can be used in the metal-containing layer, provided that the effects of the present invention are not impaired. In this case, the total content of the additives is typically about 5% by mass or less in the other resin-containing layer (or in each layer if there is one or more other resin-containing layers), but is not limited thereto. The other resin-containing layer may be either a layer containing a metal component or a layer not containing a metal component, although a layer not containing a metal component may be particularly preferred. Furthermore, the content of the resin component in the other resin-containing layer is typically the remainder excluding the additives. Therefore, it can be set to, for example, about 95 to 100% by mass, but is not limited thereto.

[0051] The plastic substrate (I) may be configured, as described above, not only from a metal-containing layer alone, but also from a multi-layer structure including other resin-containing layers. That is, the plastic substrate in the laminate of the present invention may be either (a) configured from one or more metal-containing layers, or (b) configured from one or more metal-containing layers and one or more other resin-containing layers.

[0052] In the case of (b) above, the thickness composition ratio of the metal-containing layer (M) to the other resin-containing layer (R) is not particularly limited, and the ratio [(Rt) / (Mt)] of the total thickness (Mt) of the metal-containing layer (M) to the total thickness (Rt) of the other resin-containing layer (R) is preferably 1 / 1000 to 1000 / 1, more preferably 1 / 100 to 100 / 1 in terms of facilitating control of the thickness of each layer, and most preferably 1 / 10 to 10 / 1.

[0053] The thickness of the plastic substrate (I) can be appropriately selected depending on the mechanical strength required for the gas barrier laminate to be obtained. In particular, for reasons of mechanical strength, ease of handling, etc., the thickness of the plastic substrate (I) can be set within a range of usually about 5 to 99.95 μm, and is particularly preferably 5 to 50 μm, further preferably 5 to 40 μm, and most preferably 10 to 30 μm.

[0054] (1-2) Gas Barrier Layer (II) The gas barrier layer (II) constituting the laminate of the present invention contains a polycarboxylic acid. The polycarboxylic acid in the gas barrier layer (II) can exhibit gas barrier properties by reacting with a metal component in the plastic substrate (I) (metal-containing layer).

[0055] The polycarboxylic acid may be a compound (including a polymer) having two or more carboxyl groups in the molecule, and these carboxyl groups may form an anhydride structure.

[0056] Specific examples of polycarboxylic acids include 1,2,3,4-butanetetracarboxylic acid, polyacrylic acid, polymethacrylic acid, acrylic acid-methacrylic acid copolymer, acrylic acid-maleic acid copolymer, polymaleic acid, olefin-maleic acid copolymers such as ethylene-maleic acid copolymer, polysaccharides having carboxyl groups in the side chains such as alginic acid, carboxyl group-containing polyamides, carboxyl group-containing polyesters, etc. The above polycarboxylic acids can be used alone or in combination of two or more.

[0057] When the polycarboxylic acid is a polymer, its weight average molecular weight is not limited, but is usually about 1,000 to 1,000,000, preferably 10,000 to 150,000, and more preferably 15,000 to 110,000.

[0058] Furthermore, as will be described later in connection with the production method, it is preferable that 0.1 to 20 mol % (particularly 5 to 15 mol %) of the carboxyl groups of the polycarboxylic acid be neutralized with an alkali compound, thereby achieving even better gas barrier properties.

[0059] In the present invention, among the above polycarboxylic acids, it is preferable to use at least one of polyacrylic acid, acrylic acid-maleic acid copolymer, and olefin-maleic acid copolymer. Among these, olefin-maleic acid copolymer is preferable. In particular, ethylene-maleic acid copolymer (hereinafter sometimes abbreviated as "EMA") can be preferably used from the viewpoint of gas barrier properties.

[0060] EMA can be obtained, for example, by polymerizing maleic anhydride and ethylene by a known method such as solution radical polymerization. In a dry state, the maleic acid units in an olefin-maleic acid copolymer tend to form a maleic anhydride structure in which adjacent carboxyl groups are cyclodehydrated, but in a wet state or in an aqueous solution, they undergo ring-opening to form a maleic acid structure. Therefore, in the present invention, unless otherwise specified, maleic acid units and maleic anhydride units are collectively referred to as "maleic acid units."

[0061] The content of maleic acid units in EMA is not particularly limited, but is usually preferably 5 mol% or more, more preferably 20 mol% or more, even more preferably 30 mol% or more, and most preferably 35 mol% or more. The upper limit of the maleic acid unit content is not particularly limited, but is usually 90 mol% or less, and particularly preferably 80 mol% or less. The weight-average molecular weight of EMA is also not particularly limited, but is usually preferably about 1,000 to 1,000,000, more preferably 3,000 to 500,000, even more preferably 7,000 to 300,000, and most preferably 10,000 to 200,000.

[0062] The gas barrier layer (II) may contain 100% by mass or less (for example, 50 to 80% by mass, or for example, 60 to 75% by mass) of polycarboxylic acid, and may contain other components. In the present invention, it is particularly preferable to contain a polyalcohol as the other component. By containing a polyalcohol, the polycarboxylic acid in the gas barrier layer (II) not only reacts with the metal components in the plastic substrate (I), but also reacts with the polyalcohol, thereby further improving the gas barrier properties. Therefore, the gas barrier layer may contain, for example, about 20 to 50% by mass, and preferably 25 to 40% by mass, of polyalcohol.

[0063] The polyalcohol is not limited to, but may be, for example, a compound having two or more hydroxyl groups in one molecule. These compounds may be either low molecular weight compounds or high molecular weight compounds. These compounds may be used alone or in combination of two or more.

[0064] Examples of the low molecular weight compounds include sugar alcohols such as glycerin and pentaerythritol, monosaccharides such as glucose, disaccharides such as maltose, and oligosaccharides such as galactooligosaccharides.

[0065] Examples of the polymer compound include polyvinyl alcohol (PVA), vinyl alcohol polymers such as ethylene-vinyl alcohol copolymers, and polysaccharides such as starch. The saponification degree of the polyvinyl alcohol, ethylene-vinyl alcohol copolymer, etc. is not particularly limited, but is preferably 95 mol% or more, and more preferably 98 mol% or more. Furthermore, the average polymerization degree of the polyvinyl alcohol, ethylene-vinyl alcohol copolymer, etc. is not particularly limited, but is usually preferably about 50 to 2,000, and more preferably 200 to 1,000.

[0066] In the present invention, these polyalcohols can be used alone or in combination of two or more kinds, with polyvinyl alcohol being particularly preferred.

[0067] The ratio of polycarboxylic acid to polyalcohol in the gas barrier layer (II) is not limited as long as the desired effect is obtained, but the molar ratio of OH groups to COOH groups (OH groups / COOH groups) is usually preferably 0.01 to 20, more preferably 0.01 to 10, particularly preferably 0.02 to 5, and most preferably 0.04 to 2.

[0068] The gas barrier layer (II) may also contain at least one of polyacrylamide, polymethacrylamide, and polyamine (collectively referred to as "polyamine, etc."). By incorporating these compounds, the polycarboxylic acid in the gas barrier layer (II) not only reacts with the metal components in the plastic substrate (I) but also with these compounds, thereby further improving the gas barrier properties and aroma retention. Known or commercially available polyamines, etc., can be used.

[0069] In the present invention, it is particularly preferable to use polyamines. Polyamines having two or more amino groups of at least one type selected from primary and secondary amino groups in the molecule can be used. Specific examples include polyallylamine, polyvinylamine, branched polyethyleneimine, linear polyethyleneimine, polylysine, polysaccharides having amino groups in their side chains such as chitosan, and polyamides having amino groups in their side chains such as polyarginine. These can be used alone or in combination of two or more. Furthermore, the weight-average molecular weight of the polyamine is not limited, but is usually preferably 5,000 to 150,000.

[0070] The mass ratio of the polyamine or the like to the polycarboxylic acid (polyamine or the like / polycarboxylic acid) in the gas barrier layer (II) is not particularly limited, but from the viewpoint of improving the gas barrier property, it is usually preferably about 12.5 / 87.5 to 27.5 / 72.5.

[0071] The gas barrier layer (II) may contain a crosslinking agent. The inclusion of a crosslinking agent can enhance gas barrier properties. The content of the crosslinking agent in the gas barrier layer (II) is preferably 0.1 to 30 parts by mass, and more preferably 1 to 20 parts by mass, per 100 parts by mass of polycarboxylic acid. Examples of crosslinking agents include a) self-crosslinking compounds and b) compounds having multiple functional groups reactive with carboxyl groups within the molecule. When the gas barrier layer (II) contains a polyalcohol, a compound having multiple functional groups reactive with hydroxyl groups within the molecule may also be used. Preferred crosslinking agents include at least one of isocyanate compounds, melamine compounds, urea compounds, epoxy compounds, carbodiimide compounds, zirconium salt compounds such as ammonium zirconium carbonate, and metal alkoxides.

[0072] Metal alkoxides are compounds containing metals with alkoxy groups bonded thereto. Examples of metal alkoxides that can be used include a) metal alkoxides in which halogens are bonded in place of some of the alkoxy groups, and b) metal alkoxides in which alkyl groups substituted with functional groups reactive with carboxyl groups are bonded in place of some of the alkoxy groups.

[0073] Examples of the metal in the metal alkoxide include atoms of Si, Al, Ti, Zr, etc. Note that the metal in the present invention also includes metalloids such as Si.

[0074] Examples of the halogen include chlorine, iodine, and bromine. Examples of the functional group reactive with a carboxyl group include an epoxy group, an amino group, an isocyanate group, and a ureido group. Furthermore, examples of the alkyl group include a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, and an isobutyl group.

[0075] Specific examples of such metal alkoxides include at least one of alkoxysilane compounds such as tetramethoxysilane, tetraethoxysilane, chlorotriethoxysilane, 3-glycidoxypropyltrimethoxysilane, 3-glycidoxypropyltriethoxysilane, 3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, 3-ureidopropyltriethoxysilane, and 3-isocyanatopropyltriethoxysilane; alkoxytitanium compounds such as tetraisopropoxytitanium and tetraethoxytitanium; alkoxyaluminum compounds such as triisopropoxyaluminum; and alkoxyzirconium compounds such as tetraisopropoxyzirconium.

[0076] These metal alkoxides may be (a) partially or completely hydrolyzed, (b) partially hydrolyzed and condensed, (c) completely hydrolyzed and partially condensed, or (d) a combination thereof.

[0077] When the metal alkoxide and the polycarboxylic acid are mixed, they may react with each other, making it difficult to apply the coating, so it is preferable to form a hydrolysis-condensation product in advance before mixing. As a method for forming the hydrolysis-condensation product, any of the methods used in the known sol-gel method can be applied.

[0078] The gas barrier layer (II) may contain additives such as heat stabilizers, antioxidants, reinforcing materials, pigments, anti-degradants, weathering agents, flame retardants, plasticizers, release agents, lubricants, preservatives, wetting agents, viscosity modifiers, and antifoaming agents, as long as the gas barrier properties and adhesion to the plastic substrate (I) are not significantly impaired. Examples of heat stabilizers, antioxidants, and anti-degradants include hindered phenols, phosphorus compounds, hindered amines, sulfur compounds, copper compounds, and alkali metal halides. These may be used alone or in combination of two or more.

[0079] In particular, examples of the reinforcing material include inorganic fillers or carbon-based fillers such as clay, talc, wollastonite, silica, alumina, calcium silicate, sodium aluminate, sodium aluminosilicate, magnesium silicate, glass balloons, carbon black, zeolite, montmorillonite, hydrotalcite, fluorine mica, metal fibers, metal whiskers, ceramic whiskers, potassium titanate whiskers, boron nitride, graphite, glass fibers, carbon fibers, fullerenes (C60, C70, etc.), and carbon nanotubes.

[0080] The total content of these additives is usually about 5 mass % or less in the gas barrier layer, but is not limited to this. If any of these additives has a function similar to that of any of the polycarboxylic acids, polyalcohols, polyamines, etc. that constitute the gas barrier layer, the content of that additive is considered to be the content of the polycarboxylic acid, etc., and is not included in the "additive content."

[0081] In the present invention, the thickness of the gas barrier layer (II) laminated on the plastic substrate (I) is not particularly limited, but from the viewpoint of sufficiently enhancing the gas barrier properties of the gas barrier laminate particularly after stretching, it is preferably 0.05 μm or more, more preferably 0.10 μm or more, and most preferably 0.15 μm or more. Furthermore, from the viewpoint of suppressing a deterioration in the performance of the gas barrier layer (II) or from the viewpoint of economy, it is preferably 5.00 μm or less, more preferably 1.00 μm or less, and of these, most preferably 0.50 μm or less.

[0082] (2) Layer Structure and Properties of the Laminate of the Present Invention (2-1) Structure of the Laminate The laminate of the present invention basically comprises a plastic substrate (I) including a metal-containing layer and a gas barrier layer (II). However, as long as the metal-containing layer (M) and the gas barrier layer (II) are in contact with each other, they may each be composed of one layer or two or more layers as described above.

[0083] In particular, when the plastic substrate (I) is a multilayer film, the laminate of the present invention may contain another resin-containing layer (R), as long as the metal-containing layer (M) and the gas barrier layer (II) are in direct contact with each other, and is not particularly limited, for example, as follows: a. "(R) / (M) / (II)", b. "(M) / (R) / (M) / (II)", c. "(II) / (M) / (R) / (II)", d. "(II) / (M) / (R) / (M) / (II)".

[0084] In these configurations, at least the gas barrier layer (II) and the metal-containing layer (M) are in contact with each other, and the polycarboxylic acid in the gas barrier layer (II) and the metal component in the metal-containing layer (M) are likely to react with each other, so that gas barrier properties can be efficiently obtained. Among these, in consideration of the facilities for production, operability, etc., the above-mentioned "(R) / (M) / (II)" configuration is preferred.

[0085] (2-2) Properties of the Laminate The laminate of the present invention has the following gas barrier properties, etc. In measuring the gas barrier properties, the gas barrier laminate is subjected to a retort treatment at 120°C for 30 minutes and then used as a measurement sample.

[0086] More specifically, the retort treatment for measuring the gas barrier property can be carried out by treating the entire laminate for 30 minutes in a sealed container with a hot water spray at 120° C. As such a retort treatment apparatus, for example, a commercially available hot water spray type "RCS-100 / 10SPXG" manufactured by Hisaka Seisakusho Co., Ltd. can be used.

[0087] (2-2-1) Elastic Modulus (Composite Elastic Modulus) The laminate of the present invention is subjected to retort treatment at 120°C for 30 minutes, and the elastic modulus of the surface of the gas barrier layer (II) of the gas barrier laminate is measured by nanoindentation. The elastic modulus is 9.0 to 12.5 GPa, preferably 9.5 to 12.0 GPa, and more preferably 10.0 to 11.5 GPa. This allows the gas barrier layer (II) to exhibit excellent gas barrier properties and aroma retention properties in a high-temperature, high-humidity environment, even when stress such as bending is applied to the gas barrier layer (II), as in the case of vacuum packaging, for example. In other words, the laminate has high resistance (flexibility) to bending and other stresses applied during vacuum packaging, and therefore can exhibit excellent gas barrier properties and aroma retention properties in a high-temperature, high-humidity environment. If the elastic modulus is less than 9.0 GPa, the thickness or quality of the gas barrier layer (II) may become non-uniform, or there may be a high possibility of coating defects or the crosslinking reaction not being promoted (e.g., poor composition of the coating liquid for the gas barrier layer (II)). Therefore, when stress is applied to the gas barrier layer (II), the gas barrier layer (II) may not exhibit excellent gas barrier properties and aroma retention properties in a high-temperature, high-humidity environment. If the elastic modulus exceeds 12.5 GPa, for the same reason as above, when stress is applied to the gas barrier layer (II), such as in vacuum packaging, the gas barrier layer (II) may not exhibit excellent gas barrier properties and aroma retention properties in a high-temperature, high-humidity environment. The elastic modulus here is a value measured using a nanoindenter. The elastic modulus refers to the value measured when an indenter is pressed into the surface of the gas barrier layer (II) of the gas barrier laminate.

[0088] (2-2-2) Hardness When the laminate of the present invention is retorted at 120°C for 30 minutes and the surface of the gas barrier layer (II) is measured by nanoindentation, the hardness is preferably 0.7 to 1.3 GPa, more preferably 0.8 to 1.2 GPa, and most preferably 0.9 to 1.1 GPa. This allows the gas barrier layer (II) to exhibit excellent gas barrier properties and aroma retention properties under high temperature and high humidity conditions, even when physical stress is applied to the gas barrier layer (II), for example, during vacuum packaging. The hardness refers to the value measured when an indenter is pressed into the gas barrier layer (II) of the gas barrier laminate.

[0089] (2-2-3) Oxygen permeability after elongation (temperature 40°C and humidity 90% RH) The laminate of the present invention is subjected to a retort treatment at 120°C for 30 minutes, and then simultaneously elongated in both the MD and TD directions at a rate of 1.5% / s in an environment of a temperature of 35°C and a humidity of 50%. The oxygen permeability after elongation is 100 ml / (m ２ ·day·MPa) or less, and preferably 80 ml / (m ２ · day · MPa) or less, and ２ ·day·MPa) or less. This allows the product to exhibit excellent gas barrier properties and aroma retention even when subjected to physical stress, for example, by vacuum packaging. The lower limit of the oxygen permeability is, for example, 10 ml / (m ２ ·day·MPa), but is not limited to this.

[0090] The device used for stretching after retort treatment is not particularly limited, and for example, a biaxial stretching device for research and development "Karo IV" manufactured by BRUCKNER can be used, and simultaneous stretching in MD / TD can be performed by 7% at a rate of 1.5% / s. The size of the sample to be stretched is not particularly limited, and it is sufficient as long as it is a size (e.g., 10 cm x 10 cm) that allows oxygen permeability to be measured. The temperature and humidity during stretching should be 35°C and 50% RH, simulating the working environment of vacuum packaging.

[0091] For example, in retort products (vacuum-packed foods, etc.) in which solids such as corn are vacuum-packed, the corn is pre-cooked (raw corn is boiled) before packaging, then filled into a packaging bag and vacuum-packed. Retort processing is then performed for sterilization. During the retort processing step, heat and pressure are also applied to the packaging bag, resulting in a decrease in the base material strength or gas barrier properties of the packaging bag itself and a decrease in flexibility. To evaluate the gas barrier properties under such harsh processing conditions, the laminate of the present invention was also stretched after being subjected to stress due to heat and pressure caused by retort processing.

[0092] In particular, when the gas barrier layer (II) is non-uniform in thickness or quality, or when defects such as holes or crosslinking reactions occur, stretching and / or bending / refraction occur, which can cause defects such as cracks to occur locally in the gas barrier layer (II) or can lead to thinning of the layer, resulting in an extreme deterioration of gas barrier properties. In contrast, the product of the present invention can maintain excellent gas barrier properties and aroma retention properties under harsh conditions such as a temperature of 40°C and a humidity of 90% RH, even if the laminate is stretched, bent, or refracted after retort treatment. Furthermore, the product of the present invention is a gas barrier laminate that can exhibit excellent gas barrier properties and aroma retention properties under high-temperature and high-humidity conditions after vacuum packaging, even when used in hot water sterilization (boiling) treatments other than retort treatment.

[0093] (2-2-4) Oxygen permeability before elongation (temperature 40°C and humidity 90% RH) The laminate of the present invention, after being subjected to a retort treatment at 120°C for 30 minutes, has an oxygen permeability of typically 50 ml / (m) at a temperature of 40°C and a humidity of 90% RH before elongation. ２ ·day·MPa) or less, and preferably 40 ml / (m ２ The lower limit of the oxygen permeability is, for example, 1 ml / (m ２ ·day·MPa), but is not limited to this.

[0094] (2-2-5) Oxygen permeability after elongation (temperature 20°C and humidity 90% RH) The laminate of the present invention is subjected to a retort treatment at 120°C for 30 minutes, and then simultaneously elongated by 7% in both the MD and TD directions at a rate of 1.5% / s in an environment of a temperature of 35°C and a humidity of 50%. The oxygen permeability after elongation in an environment of a temperature of 20°C and a humidity of 90% is usually 70 ml / (m ２ ·day·MPa) or less, and preferably 50 ml / (m ２ The lower limit of the oxygen permeability is, for example, 1 ml / (m ２ ·day·MPa), but is not limited to this.

[0095] (2-2-6) Oxygen permeability before elongation (temperature 20°C and humidity 90% RH) The laminate of the present invention, after being subjected to a retort treatment at 120°C for 30 minutes, has an oxygen permeability of typically 40 ml / (m) at a temperature of 20°C and a humidity of 90% RH before elongation. ２ ·day·MPa) or less, and preferably 35 ml / (m ２ The lower limit of the oxygen permeability is, for example, 0 ml / (m ２ ·day·MPa), but is not limited to this.

[0096] (2-2-7) Oxygen Permeability After Bending (Temperature 20°C and Humidity 90% RH, Temperature 40°C and Humidity 90% RH) It is desirable that the laminate of the present invention has high gas barrier properties even after being bent. More specifically, as shown in Test Example 1 described later, a laminate film (test sample) obtained by laminating a 50 μm thick unstretched polypropylene film to the gas barrier layer of the laminate of the present invention via a 4 μm thick two-component curing polyurethane adhesive layer was subjected to repeated bending fatigue tests 10 times in accordance with ASTM F392 using a Gelbo Flex Tester under an environment of temperature 23°C and humidity 50% RH, and the oxygen permeability of the test sample under an environment of temperature 20°C and humidity 90% RH was usually 50 ml / (m ２ ·day·MPa) or less, and particularly 40 ml / (m ２ The lower limit of the oxygen permeability is, for example, 0 ml / (m ２ Furthermore, the oxygen permeability of the test sample after the above treatment under an environment of a temperature of 40°C and a humidity of 90% RH is usually set to about 100 ml / (m ２ ·day·MPa) or less, and particularly 80 ml / (m ２ ·day·MPa) or less, and ２ The lower limit of the oxygen permeability is, for example, 10 ml / (m ２ ·day·MPa), but is not limited to this.

[0097] (2-2-8) Oxygen Permeability Evaluated by Image Processing As shown in Test Example 1 below, the gas barrier properties of the laminate of the present invention can also be evaluated by image processing of a test sample after the same treatment as described above. More specifically, using a test sample processed 10 times with the Gelbo Flex Tester, a three-sided bag with external dimensions of 100 mm wide x 150 mm high, prepared so that the sealant layer faces the inner surface, is filled with a predetermined preparation liquid (blue) and then heat-sealed. The sealed three-sided bag is then subjected to a retort treatment at 120°C for 30 minutes. When the three-sided bag is then photographed on a white piece of paper, blue-colored areas are observed in the image. These areas represent areas through which oxygen has permeated due to defects in the gas barrier layer (II). The gas barrier properties are then evaluated based on the area ratio of the blue area to the total area of ​​the photographed three-sided bag. A smaller area ratio indicates higher gas barrier properties. In the gas barrier laminate of the present invention, the area ratio of the blue portion in the above evaluation method is usually preferably 0.3% or less, and more preferably less than 0.1%.

[0098] (2-2-9) Aroma Retention The laminate of the present invention also has excellent aroma retention. That is, when the laminate of the present invention is used to seal contents, it is possible to effectively prevent or inhibit leakage of aromatic components contained in the contents to the outside. As a result, when food or the like is used as the contents, the aroma of the food or the like can be maintained for a relatively long period of time. The aroma retention in the present invention can be evaluated by the method shown in Test Example 1 below. In terms of aroma retention using this method, it is preferable that the concentration of leaked ethanol is 0.1% by mass or less, and more preferably less than 0.5% by mass.

[0099] (2-2-10) Tensile Strength The laminate of the present invention preferably has a tensile strength of 150 MPa or more, more preferably 180 MPa or more, in a tensile test measured in accordance with Japanese Industrial Standard "JIS K7127" at a temperature of 23°C and a humidity of 50% RH. If the tensile strength is less than 150 MPa, the mechanical strength is insufficient and the puncture strength tends to decrease. Therefore, the tensile strength can be set to, for example, about 150 to 300 MPa, but is not limited thereto.

[0100] (2-2-11) Tensile Elongation The laminate of the present invention preferably has a tensile elongation of 60% or more, more preferably 80% or more, in a tensile test measured in accordance with Japanese Industrial Standard "JIS K7127" at a temperature of 23°C and a humidity of 50% RH, from the same viewpoint as for tensile strength. Therefore, the tensile elongation can be set to, for example, about 60 to 95%, but is not limited thereto.

[0101] (2-2-12) Transparency The transparency of the laminate of the present invention is preferably such that the haze measured in accordance with Japanese Industrial Standard "JIS K7136" at a temperature of 23°C and a humidity of 50% RH is 70% or less, more preferably 50% or less, even more preferably 30% or less, particularly preferably 15% or less, and most preferably 10% or less. However, this is not limited to the above, as transparency may not be required depending on the application. The lower limit of the haze can be, for example, 1%, but is not limited thereto.

[0102] (2-2-13) Pinhole Resistance The pinhole resistance of the laminate of the present invention is preferably such that the number of pinholes generated in a 500-cycle repeated bending fatigue test in an atmosphere at 5°C is 100 or less, and more preferably 20 or less. The pinhole resistance is evaluated in accordance with ASTM F392 by measuring the number of pinholes generated after 500 cycles of bending at 5°C using a Gelbo Flex Tester (for example, manufactured by Tester Sangyo Co., Ltd.). The lower limit of the number of pinholes generated is preferably as close to 0 as possible, and can be set to 0, for example, but is not limited to this. The laminate sample (measurement area) used for pinhole resistance evaluation is 27 cm x 20 cm.

[0103] (2-2-14) Thickness The total thickness (total thickness) of the laminate of the present invention is 100 μm or less, and can be set appropriately within that range depending on the application, etc. From the viewpoints of reducing the amount of material used and bag formability, the thinner the total thickness, the more preferable, and 50 μm or less is particularly preferable, and 30 μm or less is most preferable. Furthermore, from the viewpoint of barrier properties, the thicker the total thickness, the more preferable, and 5 μm or more is particularly preferable, and 10 μm or more is more preferable. Therefore, for example, the thickness can be set within the range of 5 to 100 μm.

[0104] 2. Method for Producing Gas Barrier Laminate The laminate of the present invention can be produced by any method as long as it has the above-mentioned characteristics. In particular, the laminate of the present invention can be suitably produced by the following method: a method for producing a gas barrier laminate, comprising: (1) a step of preparing a raw material solution containing a polycarboxylic acid, a mineral oil, and an acetylene glycol-based nonionic surfactant, wherein the mass ratio of the mineral oil to the acetylene glycol-based nonionic surfactant is 80 / 20 to 40 / 60 (raw material solution preparation step), and (2) a step of applying the raw material solution as a coating liquid for forming a gas barrier layer (II) onto at least the surface of a metal-containing layer of a plastic substrate (I) including the metal-containing layer containing at least one of a metal and a metal compound and a resin component (coating step).

[0105] In the raw material liquid preparation step, a raw material liquid is prepared which contains a polycarboxylic acid, a mineral oil, and an acetylene glycol-based nonionic surfactant, and in which the mass ratio of the mineral oil to the acetylene glycol-based nonionic surfactant is 80 / 20 to 40 / 60.

[0106] From the viewpoint of workability, the raw material liquid is preferably aqueous (a liquid in which the solvent is a water-based solvent). Therefore, the polycarboxylic acid, and further the optional components such as polyalcohol and polyamine, are preferably water-soluble or water-dispersible, and more preferably water-soluble.

[0107] As the polycarboxylic acid, various polycarboxylic acids listed in "1. Gas barrier laminate" above can be used. In addition, as the polyalcohol, etc., those listed in "1. Gas barrier laminate" above can also be used.

[0108] The raw material liquid may be an aqueous solution or dispersion of polycarboxylic acid obtained by mixing a polycarboxylic acid or the like with water. In this case, the concentration of the polycarboxylic acid in the raw material liquid may be, but is not limited to, about 5 to 30% by mass.

[0109] Furthermore, when preparing an aqueous raw material solution using a polyalcohol in combination, the type of polyalcohol used, the ratio of polycarboxylic acid to polyalcohol, additives, etc. may follow the description in "1. Gas Barrier Laminate" above. In this case, it is preferable to add an alkali compound in an amount of 0.1 to 20 equivalent percent relative to the carboxyl groups of the polycarboxylic acid. Since polycarboxylic acids have high carboxyl group content, they become highly hydrophilic, and can be made into an aqueous solution without the addition of an alkali compound. In this case, adding an appropriate amount of an alkali compound can significantly improve the gas barrier properties of the resulting gas barrier laminate.

[0110] The alkaline compound may be any compound capable of neutralizing the carboxyl groups of the polycarboxylic acid. Examples include at least one of sodium hydroxide, potassium hydroxide, calcium hydroxide, sodium carbonate, aqueous ammonia, and sodium bicarbonate. From the viewpoint of enhancing gas barrier properties, the amount of the alkaline compound added (degree of neutralization) is usually preferably 0.1 to 20 mol % relative to the carboxyl groups of the polycarboxylic acid.

[0111] In the present invention, when preparing an aqueous coating liquid by mixing a polycarboxylic acid and a polyamine, it is preferable to add a base to the polycarboxylic acid in advance in order to suppress gelation.

[0112] The base may be any base that does not impair the gas barrier properties of the resulting gas barrier laminate. Examples include inorganic compounds such as sodium hydroxide, calcium hydroxide, and ammonia, and organic compounds such as methylamine and diethanolamine. These may be used alone or in combination of two or more. Among these, ammonia is preferred because it is easily volatilized during drying and heat treatment. From the viewpoint of suppressing gelation of the coating liquid, the amount of base added is usually preferably 0.6 equivalents or more, more preferably 0.7 equivalents or more, and most preferably 0.8 equivalents or more, relative to the carboxyl groups of the polycarboxylic acid.

[0113] In the production method of the present invention, the mineral oil has the function of homogenizing the coating liquid for forming the gas barrier layer (II) described below, in particular, and its uniform distribution can contribute to improving gas barrier properties and aroma retention.

[0114] The mineral oil is not particularly limited as long as it is a petroleum-derived hydrocarbon mixture composed of hydrocarbons, and at least one hydrocarbon mineral oil such as aromatic hydrocarbons, paraffinic hydrocarbons, and naphthenic hydrocarbons can be suitably used. Among these, it is preferable that the mineral oil has an average carbon number of 20 to 35 and is liquid at room temperature and normal pressure. Commercially available products can also be used. Examples of commercially available products that can be used include "AGITAN 282" (manufactured by MUNZING CHEMIE GmbH) and "SN DEFORMER 154S" (manufactured by SAN NOPCO).

[0115] When adding the mineral oil, water, silica particles, a polyoxyalkylene compound, a (meth)acrylic acid / (meth)acrylate alkyl copolymer (salt), an emulsifier, as well as known additives (antifreezing agents, water repellents, film-forming regulators, etc.), solvents, etc. may be used in combination, if necessary.

[0116] The amount of mineral oil added is not limited, but is preferably 0.005 to 0.15 parts by mass, more preferably 0.007 to 0.050 parts by mass, and most preferably 0.010 to 0.020 parts by mass, per 100 parts by mass of the total (solids) of polycarboxylic acid and polyalcohol in the raw material liquid.

[0117] The acetylene glycol-based nonionic surfactant also has the function of homogenizing the coating liquid for forming the gas barrier layer (II), and its uniform distribution can contribute to improving the gas barrier properties and aroma retention properties.

[0118] As the acetylene glycol-based nonionic surfactant, at least one of an acetylene glycol-based compound and its polyethylene oxide adduct can be suitably used. This is a nonionic surfactant that basically has an acetylene group located at the center of the molecule and has a bilaterally symmetrical structure with the acetylene group at the center, and for example, is represented by the following general formula (1): (wherein, R １ and R ２ are the same or different and represent a methyl group, a propyl group, or an isopropyl group. ３ and R ４ are the same or different and represent a hydroxy group or a polyethylene oxide group.

[0119] More specifically, at least one of 3,6-dimethyl-4-decyne-3,6-diol, 2,4,7,9-tetramethyl-5-decyne-diol, and 2,4,7,9-tetramethyl-5-decyne-diol-dipolyoxyethylene ether can be exemplified. Among these compounds, ethylene oxide (EO) adducts are preferred. The content of the ethylene oxide moiety in the EO adduct is not limited, but is usually about 20 to 85% by mass, and preferably 40 to 65% by mass.

[0120] Commercially available acetylene glycol-based nonionic surfactants may also be used, such as "Olfine E1004," "Olfine E1004C," "Olfine E1006," "Olfine E1010," "Olfine E1020," "Surfynol 420," and "Surfynol 440" (all manufactured by Nissin Chemical Industry Co., Ltd.).

[0121] The content of the acetylene glycol-based nonionic surfactant is preferably added so as to be 0.005 to 0.100 parts by mass, more preferably 0.007 to 0.050 parts by mass, and most preferably 0.010 to 0.020 parts by mass, relative to 100 parts by mass of the total (solid content) of the polycarboxylic acid and polyalcohol in the raw material liquid.

[0122] Depending on the type, the acetylene glycol-based nonionic surfactant in the coating solution for forming the gas barrier layer (II) may volatilize during heat treatment after application to the plastic substrate (I), and may not remain in the formed gas barrier layer (II).

[0123] When the raw material liquid contains mineral oil and an acetylene glycol-based nonionic surfactant, one of the most important conditions is the blending ratio of the mineral oil to the acetylene glycol-based nonionic surfactant.

[0124] From the viewpoint of improving resistance to elongation or bending / refraction, the blending ratio (mass ratio) of mineral oil to acetylene glycol-based nonionic surfactant is preferably in the range of 80 / 20 to 40 / 60, particularly preferably 75 / 25 to 45 / 55, even more preferably 70 / 30 to 50 / 50, and most preferably 65 / 35 to 55 / 45.

[0125] The blending ratio of the mineral oil to the acetylene glycol-based nonionic surfactant also affects the elastic modulus of the gas barrier layer (II), and when the blending ratio of the mineral oil exceeds 80, the elastic modulus of the gas barrier layer (II) tends to increase, and in some cases may exceed 12.5 GPa, which is the upper limit of the elastic modulus specified in the present invention. On the other hand, when the blending ratio of the mineral oil is less than 40, the elastic modulus of the gas barrier layer (II) tends to decrease, and may not satisfy the lower limit of 9.0 GPa of the elastic modulus specified in the present invention.

[0126] The raw material liquid may also contain other additives within the range that does not impair the effects of the present invention. Examples of additives include the various additives listed above in "1. Gas barrier laminate."

[0127] The raw material solution can be suitably prepared by using at least an aqueous solvent as a solvent and then mixing these components. In this case, mixing can be carried out using a dissolving kettle equipped with a stirrer or the like. As the aqueous solvent, 1) water or 2) a mixed solvent of water and a water-soluble organic solvent can be used. As the water-soluble organic solvent, there is no limitation, and examples thereof include monohydric alcohols such as methanol and ethanol, and polyhydric alcohols such as diethylene glycol and glycerin.

[0128] The mixing procedure is not limited, but when a polyalcohol is added, it is preferable to prepare aqueous solutions of the polycarboxylic acid and the polyalcohol separately and mix them before coating. In this case, adding the above-mentioned alkali compound to the aqueous solution of the polycarboxylic acid can improve the stability of the aqueous solution.

[0129] In the present invention, a method of preparing a preliminary dispersion and using it to prepare a raw material liquid can be suitably employed as a method for incorporating mineral oil into the raw material liquid (coating liquid for forming the gas barrier layer (II)). For example, a preliminary dispersion in which mineral oil is diluted with an aqueous solution or dispersion containing a polycarboxylic acid can be used. This allows the mineral oil (and the acetylene glycol-based nonionic surfactant) to be dispersed more uniformly in the coating liquid for forming the gas barrier layer (II), making it possible to provide a gas barrier laminate that can exhibit better gas barrier properties and aroma retention.

[0130] The method for preparing the preliminary dispersion is not limited, and examples thereof include: (a) a method in which a mixed liquid (mixed liquid a') containing polycarboxylic acid and not containing mineral oil and acetylene glycol-based nonionic surfactant is prepared separately from a mixed liquid (mixed liquid a) containing polycarboxylic acid and not containing mineral oil and acetylene glycol-based nonionic surfactant, and a preliminary dispersion is prepared by adding mineral oil (or mineral oil and acetylene glycol-based nonionic surfactant) to mixed liquid a', and then the mixed liquid a and the preliminary dispersion are mixed; and (b) a method in which a part of mixed liquid a is collected, a preliminary dispersion is prepared using the collected mixed liquid a2, and then the remaining mixed liquid a1 of the mixed liquid a is mixed with the preliminary dispersion.

[0131] From the viewpoint of more reliably dispersing the mineral oil, the proportion of the mixed liquid used to prepare the preliminary dispersion is preferably about 0.05 to 15 mass%, and more preferably 0.1 to 5 mass%, in both cases (a) and (b) above, where the total amount of the mixed liquid contained in the raw material liquid is 100 mass%. In the case of (a) above, the total amount is the total amount of mixed liquid a and mixed liquid a'. In the case of (b) above, the total amount is the total amount of mixed liquid a1 and mixed liquid a2.

[0132] In the present invention, the method (b) is preferred from the standpoints of ease of controlling the composition of the mixed liquid, production efficiency, and the like. More specifically, a method including the steps of: 1) collecting a portion (mixed liquid a2) of a mixed liquid (mixed liquid a) containing a polycarboxylic acid but not containing mineral oil or an acetylene glycol-based nonionic surfactant, and adding mineral oil (or mineral oil and an acetylene glycol-based nonionic surfactant) to the collected mixed liquid a2 to prepare a preliminary dispersion; and 2) mixing the remaining portion (mixed liquid a1) of the mixed liquid with the preliminary dispersion to prepare a coating liquid for forming a gas barrier layer (II). In this case, the mixed liquid a1 may contain mineral oil and an acetylene glycol-based nonionic surfactant, but preferably does not contain mineral oil or an acetylene glycol-based nonionic surfactant. Alternatively, two or more portions of mixed liquid a2 may be collected, and preliminary dispersions may be prepared from each portion. For example, the mixture can be divided into mixed liquid a2(1), mixed liquid a2(2), mixed liquid a2(3), . . . mixed liquid a2(n).

[0133] The content of mineral oil in the preliminary dispersion is not limited as long as it is 0.005 to 0.15 parts by mass per 100 parts by mass of the total (solid content) of polycarboxylic acid and polyalcohol in the raw material liquid (or coating liquid for forming the gas barrier layer (II)). However, from the viewpoint of avoiding content errors or improving dispersibility, it may be adjusted so that the content is 0.1 to 15 parts by mass (preferably 0.5 to 13 parts by mass, more preferably 1 to 12 parts by mass) per 100 parts by mass of the total (solid content) of polycarboxylic acid and polyalcohol in the preliminary dispersion.

[0134] The agitator used for pre-dispersion is not particularly limited, but examples include a blade agitator, a high-speed rotation homomixer, a high-pressure homogenizer, a dissolver, etc. In particular, a high-speed rotation homomixer, a high-pressure homogenizer, a dissolver, etc. are preferred, and among these, a high-speed rotation homomixer is more preferred. The device and agitation conditions used for dispersion are not particularly limited as long as they fall within the range of the median diameter in particle size distribution measurement described below, but for example, pre-dispersion is preferably performed for 5 to 30 minutes at a rotation speed of 2000 to 8000 rpm using a high-speed rotation homomixer.

[0135] Furthermore, the method for incorporating an acetylene glycol-based nonionic surfactant into the coating liquid for forming the gas barrier layer (II) is not particularly limited, but by blending and dispersing the acetylene glycol-based nonionic surfactant together with a mineral oil, the dispersion of the mineral oil can be improved. Therefore, it is preferable to blend the acetylene glycol-based nonionic surfactant when dispersing the mineral oil. Therefore, even when blending the mineral oil by the above-mentioned pre-dispersion, it is preferable to blend the acetylene glycol-based nonionic surfactant together with the mineral oil.

[0136] The content of the acetylene glycol-based nonionic surfactant in the preliminary dispersion is not particularly limited, as long as it is 0.005 to 0.100 parts by mass per 100 parts by mass of the total (solid content) of the polycarboxylic acid and polyalcohol in the raw material liquid (or coating liquid for forming the gas barrier layer (II)). However, from the viewpoint of improving resistance to elongation or bending / refraction, it may be adjusted so that the content is 0.01 to 20 parts by mass (preferably 0.05 to 15 parts by mass, more preferably 0.1 to 10 parts by mass) per 100 parts by mass of the total (solid content) of the polycarboxylic acid and polyalcohol in the preliminary dispersion.

[0137] The pre-dispersion liquid prepared as described above can be mixed with the entire mixed liquid containing, for example, polycarboxylic acid and not containing mineral oil or acetylene glycol-based nonionic surfactant to obtain a raw material liquid. In the case of (a) above, this mixed liquid corresponds to mixed liquid a. In the case of (b) above, this mixed liquid corresponds to mixed liquid a1. The method for mixing the two is not particularly limited, and can be carried out, for example, using the equipment and conditions that can be used for the pre-dispersion described above.

[0138] The resulting raw material liquid can be used as is to coat a plastic substrate with a coating liquid for forming a gas barrier layer (II), or it can be subjected to a filtration process prior to coating. Preferably, the coating liquid for forming a gas barrier layer (II) can be prepared by passing the raw material liquid through a filter with a filtration accuracy (absolute filtration accuracy) of 1.0 to 10.0 μm. Surprisingly, the above-described coating liquid preparation process can produce a film that exhibits high gas barrier properties, especially under high-temperature and high-humidity environments such as a temperature of 40°C and a humidity of 90% RH. The reason for this has yet to be clarified, but the applicant's post-hoc speculation suggests the following: Passing the raw material liquid through a filter enables the fragmentation of air bubbles contained in the raw material liquid and the removal of coarse particles. Furthermore, aggregates of polycarboxylic acid and / or polyalcohol in the raw material liquid are fragmented, facilitating more intensive reactions between the polycarboxylic acid and polyalcohol, and between the polycarboxylic acid and metal components, during gas barrier layer formation. As a result, the gas barrier layer (II) is formed to be homogeneous as a whole and free from defects such as pores and cracks.

[0139] As the filter, a filter having a filtration accuracy of 1.0 to 10.0 μm is used from the viewpoint of repelling the coating liquid or preventing its removal and forming a homogeneous gas barrier layer (II), and a filter having a filtration accuracy of 2.0 to 5.0 μm is particularly preferred.

[0140] In the present invention, in order to improve filtration efficiency and filtration performance, it is preferable to pass the raw material liquid through the filter while applying pressure. The pressure is usually in the range of 0.1 to 0.3 MPa, and particularly preferably 0.15 to 0.25 MPa. If the pressure is less than 0.1 MPa, the filtration efficiency is low. On the other hand, if the pressure is greater than 0.3 MPa, there is a risk of the filter breaking. In the present invention, a normal pressure device (e.g., a pump) can be used as the pressurizing means.

[0141] The filter device is not particularly limited as long as it has a filtration accuracy in the range of 1.0 to 10.0 μm. For example, a filter device including (a) a filter housing, (b) a filter installed in the filter housing, and (c) a pump for pressurizing and injecting the raw material liquid into the filter can be used.

[0142] As the filter (cartridge filter), a filter made of any material such as a metal mesh, filter cloth, nonwoven fabric laminate, resin molded body, or ceramic molded body can be suitably used. The shape is also not limited, and a cylindrical (chikuwa-shaped) filter can be used, for example. The size of the cylindrical filter can be, for example, but is not limited to, an outer diameter of about 50 to 100 mm, an inner diameter of about 10 to 30 mm, and a length of about 200 to 1000 mm. These devices can also be publicly known or commercially available.

[0143] The filter treatment method may be either a continuous method or a circulation method. The number of times the material is passed through the filter may be one or two or more times (multi-stage method). Therefore, for example, a method may be employed in which the material is passed through a first filter having a filtration accuracy of 1.0 to 10.0 μm, and then passed through a second filter having a filtration accuracy of 1.0 to 10.0 μm but smaller than the first filter.

[0144] In the present invention, the viscosity of the coating liquid when passed through the filter is not particularly limited, but it is preferable that the viscosity be within the range of 5.0 to 50.0 mPa·s when measured at a liquid temperature of 25°C using a Brookfield viscometer. By setting the liquid viscosity before passing through the filter within this range, the fragmentation of bubbles can be further promoted. In addition, the effect of promoting the fragmentation of aggregates of polycarboxylic acid and / or polyalcohol can also be expected. Therefore, if the viscosity of the coating liquid before passing through the filter is outside the above range, the viscosity of the coating liquid can be adjusted as necessary.

[0145] In the present invention, the coating liquid for forming the gas barrier layer (II) is typically in the form of an aqueous dispersion (emulsion or dispersion) using an aqueous solvent. In this case, the droplet size is not limited, but from the viewpoint of the homogeneity of the gas barrier layer (II), the median diameter (D50) is preferably 0.1 to 0.6 μm, more preferably 0.15 to 0.55 μm, and most preferably 0.2 to 0.5 μm. If the median diameter is less than 0.1 μm, there is a high possibility that the mineral oil or acetylene glycol-based nonionic surfactant will be removed or adsorbed to the filter when the raw material liquid is passed through a filter, which may prevent the formation of a homogeneous gas barrier layer (II). As a result, high gas barrier properties will not be achieved under an environment of 40°C and 90% RH after elongation, and further gas barrier properties may be further reduced due to localized elongation and / or bending / refraction. Furthermore, if the median diameter exceeds 0.6 μm, even if the raw material liquid is passed through a filter, aggregates or undissolved polycarboxylic acid and / or polyalcohol and aggregates of mineral oil in the raw material liquid will pass through the filter, causing repellency of the coating liquid or coating loss due to these. In such cases, a homogeneous gas barrier layer (II) cannot be obtained, and therefore high gas barrier properties cannot be obtained after elongation under an environment of a temperature of 40° C. and a humidity of 90% RH.

[0146] Coating Step In the coating step, the gas barrier layer-forming coating liquid is applied onto at least the surface of the metal-containing layer of the plastic substrate (I) that includes a metal-containing layer that contains at least one of a metal and a metal compound and a resin component.

[0147] The plastic substrate (I) includes a metal-containing layer containing at least one of a metal and a metal compound and a resin component, and the configuration described above in "1. Gas barrier laminate" can be adopted. In particular, a plastic substrate arranged so that the metal-containing layer is exposed can be preferably used. For example, a film preformed from a resin-containing raw material can be used as such a substrate. In addition, the manufacturing method of the plastic substrate (I) is not particularly limited, and for example, a plastic substrate (I) manufactured as follows can also be used.

[0148] In the case of a plastic substrate (I) consisting of a single-layer film, for example, a thermoplastic resin mixed with a metal component is heated and melted in an extruder, extruded into a film form from a T-die, and cooled and solidified on a rotating cooling drum by a known casting method such as air knife casting or electrostatic casting, to obtain an unstretched film, which can be used as the plastic substrate (I).

[0149] In addition, in the case of a plastic substrate (I) made of a multilayer film, for example, a thermoplastic resin mixed with a metal component is heated and melted in an extruder A, and a thermoplastic resin is heated and melted in an extruder B, and the two melted resins are superimposed in a die, and for example, a film that can be a two-layer structure of a metal-containing layer (M) / a resin layer (R) is extruded from a T-die, and similarly to the above, it can be obtained as an unstretched film by cooling and solidifying.The film thus obtained can be used as the plastic substrate (I).By using each of these methods, by incorporating metal into the plastic substrate (I), it is also possible to omit the step of laminating a layer containing a metal component on the substrate.

[0150] The plastic substrate (I) may be subjected to a surface treatment such as corona discharge treatment, if necessary, before the application of the coating liquid for forming the gas barrier layer (II). These treatment methods themselves can be carried out according to known methods.

[0151] The method for applying the coating liquid for forming the gas barrier layer (II) to the plastic substrate (I) is not particularly limited, and for example, a method using one or a combination of two or more of an air knife coater, kiss roll coater, metalling bar coater, gravure roll coater, reverse roll coater, dip coater, die coater, etc. can be used.

[0152] After the coating liquid for forming the gas barrier layer (II) has been applied to the plastic substrate (I), a drying step for drying the coating film can be carried out as necessary.

[0153] The drying method is not particularly limited, and examples thereof include a) a method in which a heat treatment is carried out immediately after application, and the formation of a dry film and the heat treatment are carried out simultaneously; and b) a method in which, after application, water and the like are evaporated by blowing hot air from a dryer or the like, irradiating with infrared rays, or the like, to form a dry film, and then the heat treatment is carried out.

[0154] In the present invention, it is preferred to carry out a heat treatment immediately after coating, unless this will cause any particular damage to the state of the gas barrier layer (II) or its physical properties such as gas barrier properties.

[0155] The heat treatment method is not particularly limited, and examples thereof include a method of performing heat treatment in a dry atmosphere such as an oven. In consideration of shortening the process, it is preferable to stretch the plastic substrate (I) after applying the coating liquid for forming the gas barrier layer (II). In either of the above cases, it is preferable to perform heat treatment on the plastic substrate (I) on which the gas barrier layer (II) has been formed in a heated atmosphere of 100°C or higher for 5 minutes or less.

[0156] Furthermore, when the gas barrier layer (II) contains a polycarboxylic acid and a polyalcohol, the heat treatment temperature after application of the coating liquid cannot be generalized because it can be affected by the ratio between them, the presence or absence of additional components, the content of the additives, etc., but is usually preferably 100 to 300° C., more preferably 120 to 250° C., even more preferably 140 to 240° C., and most preferably 160 to 220° C. If the heat treatment temperature is less than 100° C., the crosslinking reaction between the polycarboxylic acid and the polyalcohol cannot proceed sufficiently, making it difficult to obtain a laminate with sufficient gas barrier properties, whereas if the heat treatment temperature exceeds 300° C., the gas barrier layer (II) etc. may become embrittled.

[0157] The heat treatment time is usually preferably 5 minutes or less, more preferably 1 second to 5 minutes, even more preferably 3 seconds to 2 minutes, and most preferably 5 seconds to 1 minute. If the heat treatment time is too short, the crosslinking reaction cannot proceed sufficiently, making it difficult to obtain a laminate with gas barrier properties. On the other hand, if the heat treatment time is too long, productivity decreases.

[0158] The coating liquid for forming the gas barrier layer (II) applied to the plastic substrate (I) may be subjected to a high-energy ray irradiation treatment such as ultraviolet rays, X-rays, electron beams, etc., before or after the drying, as necessary. In such cases, a component that crosslinks or polymerizes upon high-energy ray irradiation may be blended.

[0159] Stretching Step In the present invention, the stretching step preferably further comprises a step of subjecting the laminate coated with the gas barrier layer-forming coating liquid to simultaneous biaxial stretching or sequential biaxial stretching.

[0160] The stretching method may be either simultaneous biaxial stretching or sequential biaxial stretching, with simultaneous biaxial stretching being particularly preferred. Simultaneous biaxial stretching generally provides practical properties such as mechanical properties, optical properties, thermal dimensional stability, and pinhole resistance. In addition, sequential biaxial stretching, in which longitudinal stretching is followed by transverse stretching, tends to increase the frequency of film breakage when the blending amount of metal components is high, as orientation crystallization of the film progresses during longitudinal stretching, reducing the stretchability of the thermoplastic resin during transverse stretching. For this reason, in the present invention, it is preferable to perform a water absorption treatment and then use the simultaneous biaxial stretching method.

[0161] In the case of simultaneous biaxial stretching, for example, a coating liquid for forming a gas barrier layer (II) is applied to a plastic substrate (I) to form a gas barrier layer (II), and then simultaneous biaxial stretching is carried out in the machine direction (MD) and the transverse direction (TD) using a tenter-type simultaneous biaxial stretching machine, thereby obtaining a simultaneously biaxially stretched gas barrier laminate.

[0162] In the case of sequential biaxial stretching, for example, the resulting unstretched film is stretched in the machine direction (MD), and then a coating liquid for forming the gas barrier layer (II) is applied by the above-mentioned method to form the gas barrier layer (II), and then stretching is carried out in the transverse direction (TD), thereby obtaining a sequentially biaxially stretched gas barrier laminate.

[0163] If the unstretched film is oriented, the stretchability may decrease in subsequent steps, so the unstretched film is preferably in a substantially amorphous and unoriented state.

[0164] When a polyamide resin is used as the plastic substrate (I), it is preferable to carry out a step of allowing the unstretched film to absorb water (water absorption treatment) prior to stretching. By carrying out such a treatment, the stretching stress increases, making it possible to more effectively avoid problems such as film breakage. The water absorption treatment method is not limited as long as it allows the unstretched film to absorb a certain amount of water, and may be, for example, a) a method of immersing the unstretched film in water, or b) a method of spraying water onto the unstretched film. In particular, method a) is preferred in that it allows more effective water absorption, and a method of immersing the unstretched film in warm water at about 30 to 80°C is more preferred. The amount of water to be absorbed may be set to, for example, about 0.5 to 15 parts by mass of water per 100 parts by mass of the unstretched film (i.e., a water absorption rate of 0.5 to 15%), but is not limited thereto. The immersion time is not limited, but should be long enough to achieve the above-mentioned amount of water absorption. A more specific method of water absorption treatment is, for example, transferring the unstretched film to a water tank whose temperature is controlled to 80°C or less, and immersing the film in water for 5 minutes or less (for example, about 30 seconds to 5 minutes), thereby allowing the unstretched film to absorb water to a water absorption rate of 0.5 to 15% based on the weight of the unstretched film.

[0165] The stretching ratio of the film is preferably 1.5 times or more in the case of uniaxial stretching, and also preferably 1.5 times or more in both the longitudinal and transverse directions in the case of longitudinal and transverse biaxial stretching, and can be about 1.5 to 4 times in the MD direction and about 1.5 to 4 times in the TD direction. Furthermore, the areal stretching ratio in the case of longitudinal and transverse biaxial stretching is not particularly limited, but is usually preferably 3 times or more, more preferably 6 to 20 times, and most preferably 6.5 to 13 times. Meanwhile, the stretching ratio ratio (MD stretching ratio / TD stretching ratio) in the case of longitudinal and transverse biaxial stretching is not particularly limited, but is preferably 1 / 3 to 3 / 1, and more preferably 1 / 2.5 to 2.5 / 1. A stretching ratio within this range makes it possible to obtain a gas barrier laminate with superior mechanical properties.

[0166] The stretching temperature is not limited either, and can be within the range of, for example, 40 to 220° C. In particular, in the case of sequential stretching, it is preferable that stretching in the MD direction is performed at 40 to 80° C. and stretching in the TD direction is performed at 80 to 150° C. In addition, in the case of simultaneous biaxial stretching, it is preferable that the temperature is 160 to 220° C.

[0167] The film that has been subjected to the stretching treatment step may also be subjected to a heat setting step, a relaxation step, etc., as necessary. In this case, the temperature in the heat setting step can be appropriately set within a range of usually about 150 to 300° C., and can be set, for example, to 200 to 230° C. The time for the heat setting step can be changed depending on the temperature and the like within a range of usually about 1 to 30 seconds, and can be set, for example, to 1 to 5 seconds, but is not limited thereto.

[0168] In addition, the relaxation step may generally be performed in the machine direction and / or the cross direction at a relaxation rate within a range of about 0 to 10% (preferably 2 to 6%). The temperature in the relaxation step can be appropriately set within a range of about 150 to 300°C, as in the heat setting step, but it is desirable to perform the relaxation step at a temperature lower than the maximum temperature of the heat setting treatment in order to more reliably reduce the heat shrinkage rate. The heat setting step and the relaxation step are preferably performed successively after heat setting in a tenter where a stretching treatment has been performed, for example.

[0169] If necessary, the laminate of the present invention may be subjected to a humidification treatment after any of the stretching, heat setting, and relaxation processes, in addition to the water absorption treatment described above, particularly for the purpose of enhancing gas barrier properties. This humidification treatment can further promote the reaction between the metal component of the plastic substrate (I) and the polycarboxylic acid of the gas barrier layer (II). Such humidification treatments are not limited, and examples include a) exposing the laminate to a high-temperature, high-humidity atmosphere, and b) directly contacting the laminate with high-temperature water. The humidification treatment conditions vary depending on the laminate's configuration and treatment method. However, when the laminate is left in a high-temperature, high-humidity atmosphere, a temperature of 30 to 130°C and a humidity of 50 to 100% RH are preferred. When contacting the laminate with high-temperature water, a temperature of approximately 30 to 130°C (under pressure for temperatures above 100°C) is also preferred. The humidification treatment time varies depending on the treatment conditions, but in either case, it can generally be set appropriately within a range from a few seconds to several hundred hours.

[0170] The laminate of the present invention may be subjected to a surface treatment such as corona discharge treatment, if necessary. These treatment methods can be carried out according to known methods.

[0171] 3. Use of Gas Barrier Laminate In the present invention, other layers may be laminated on the laminate as long as the effects of the present invention are not impaired. Such laminates are also included in the laminate of the present invention. The other layers are not particularly limited, and examples thereof include a substrate layer such as a polyester or polyamide layer, a sealant layer, a barrier layer, an antistatic layer, a release layer, and a printing layer. These layers may be used alone or in combination of two or more.

[0172] Examples of resins used for the sealant layer include at least one of low-density polyethylene, medium-density polyethylene, high-density polyethylene, linear low-density polyethylene, polypropylene, polyethylene / polypropylene copolymer, ethylene-vinyl acetate copolymer, ionomer resin, ethylene-acrylic acid / methacrylic acid copolymer, ethylene-acrylic acid / methacrylic acid ester copolymer, polyvinyl acetate resin, etc. Among these, polyolefin resins such as polyethylene, polypropylene, and polyethylene / polypropylene copolymer, which have high heat seal strength or material strength themselves, are preferred.

[0173] These resins may be used alone or may be copolymerized or melt-mixed with other resins, and may further be acid-modified, etc. Methods for forming a sealant layer on a gas barrier laminate are not limited, and examples include a) a method in which a film or sheet made of a sealant resin is laminated on a gas barrier laminate via an adhesive, and b) a method in which the sealant resin is extrusion-laminated on a gas barrier laminate. In the former method, the film or sheet made of the sealant resin may be in an unstretched state or in a stretched state at a low magnification, but in practical terms, it is preferably in an unstretched state.

[0174] The thickness of the sealant layer is not particularly limited, but is preferably 20 to 100 μm, and more preferably 40 to 70 μm.

[0175] The barrier layer (other than the gas barrier layer of the laminate of the present invention) may be a barrier layer employed in known films, such as a polyvinylidene chloride copolymer layer.

[0176] The laminate of the present invention can be suitably used as a packaging material for vacuum packaging applications where localized elongation stress and / or bending is likely to occur during packaging, including hot water sterilization treatments such as boiling and retort treatments. Furthermore, since it exhibits excellent gas barrier properties and aroma retention even in high-temperature and high-humidity environments where gas barrier properties are reduced, it is also suitable for long-distance transportation of contents such as food or oxygen absorbers that are susceptible to problems such as discoloration and deactivation due to oxidation.

[0177] In addition to the above-mentioned contents, the laminate of the present invention can also be used for contents such as food and beverages, fruits, juice, drinking water, alcohol, cooked foods, fish paste products, frozen foods, meat products, simmered dishes, bamboo shoots, corn, pickles, rice cakes, liquid soup, seasonings, as well as various food and beverages, liquid detergents, cosmetics, chemical products, etc., when a heat treatment step using hot water or steam is required after filling and packaging.

[0178] When the laminate of the present invention is used as a packaging bag, its form is not limited, and it can be used for, for example, two-sided bags, three-sided bags, three-sided bags with zippers, palm-seated bags, gusset bags, bottom gusset bags, stand-up bags, stand-up zipper bags, two-sided bags, four-column flat-bottom gusset bags, side-seal bags, bottom-seal bags, as well as lid materials for cup containers (cup products), draw packaging, etc. These packaging bags (packaging bags of the present invention) are also encompassed by the present invention.

[0179] In particular, even when the packaging bag of the present invention contains solid food having an uneven surface, such as corn (e.g., a surface unevenness with a height difference of 1 mm or more), and is used to produce a vacuum-packed product, the packaging bag of the present invention (laminate of the present invention) conforms to the uneven surface and adheres tightly to it when evacuated. In such cases, the laminate of the present invention is durable against the elongation stress and / or bending stress to which it is subjected, thereby achieving higher gas barrier properties and aroma retention. Therefore, the present invention also encompasses vacuum-packed products in which at least a solid food (especially a solid food having an uneven surface) is contained and sealed in the packaging bag of the present invention.

[0180] The features of the present invention will be described in more detail below with reference to examples and comparative examples, but the scope of the present invention is not limited to these examples.

[0181] 1. Regarding raw materials used The raw materials used in each example and comparative example are as follows. (1) Thermoplastic resin for constituting plastic substrate (I) PA6: Nylon 6 resin ("A1030BRF" manufactured by Unitika Ltd., relative viscosity 3.0) (2) Metal compound for constituting plastic substrate (I) MgO: Magnesium oxide ("PUREMAG FNM-G" manufactured by Tateho Chemical Industries, Ltd., average particle size 0.54 μm) (3) Metal compound-containing master chip for constituting plastic substrate (I) Master chip 1: Prepared by kneading 95 parts by mass of the PA6 and 5 parts by mass of MgO. Master chip 2: Prepared by kneading 75 parts by mass of the PA6 and 25 parts by mass of MgO. (4) Polycarboxylic acid components of coating liquid for forming gas barrier layer (II) EMA aqueous solution: EMA (weight average molecular weight 60,000) and sodium hydroxide were added to water, heated to dissolve, and then cooled to room temperature to prepare an EMA aqueous solution with a solids content of 15 mass % in which 10 mol % of the carboxyl groups of the EMA were neutralized with sodium hydroxide. PVA aqueous solution: Polyvinyl alcohol (PVA) aqueous solution with a solids content of 15 mass % prepared by adding polyvinyl alcohol (5-98, manufactured by Kuraray Co., Ltd., saponification degree 98 to 99%, average polymerization degree approximately 500) to water, heated to dissolve, and then cooled to room temperature. (5) Mineral oils "AGITAN 282" manufactured by MUNZING CHEMIE GmbH (referred to as "Mineral oil A" in the table) "SN DEFOAMER 154S" manufactured by SAN NOPCO (referred to as "Mineral oil B" in the table) "AIRASE 4655" manufactured by EVONIK (referred to as "Vegetable oil" in the table) (6) Surfactants Acetylene glycol-based nonionic surfactant: "OLFIN E1004" manufactured by Nissin Chemical Industry Co., Ltd. Anionic surfactant: "NOPCO 1338" manufactured by SAN NOPCO

[0182] 2. Examples and Comparative Examples [Example 1] Nylon 6 resin and master chip 1 were mixed so that the magnesium oxide content was 0.5% by mass. This mixture was placed in an extruder and melted in a cylinder at 270°C. The melt was extruded into a sheet from a T-die orifice and rapidly cooled by contacting it with a rotating drum cooled to 10°C, thereby obtaining a 150 μm-thick unstretched plastic substrate (I) film comprising a metal-containing layer (M). The resulting unstretched film was placed in a hot water bath at 50°C and subjected to a water absorption treatment for 2 minutes (water absorption rate 5%). Next, a mixed solution a was prepared by mixing an aqueous PVA solution and an aqueous EMA solution so that the mass ratio (solid content) of PVA to EMA was 30 / 70. Here, a preliminary dispersion was first prepared. 0.15% (sampling rate) of the total weight of the prepared mixed solution a was sampled. In this case, the removed mixed solution from the total amount of mixed solution a was designated mixed solution a2, and the remaining mixed solution was designated mixed solution a1. Mineral oil (A) was mixed with mixed solution a2, and an acetylene glycol-based nonionic surfactant was blended into mixed solution a2 so that the mass ratio of mineral oil to acetylene glycol-based nonionic surfactant was 60 / 40. The amounts of mineral oil and acetylene glycol-based nonionic surfactant added in mixed solution a2 were 0.113 parts by mass of mineral oil (A) and 0.073 parts by mass of acetylene glycol-based nonionic surfactant per 100 parts by mass of the total mass (solids) of PVA and EMA. Next, mixed solution a2 to which mineral oil (A) and acetylene glycol-based nonionic surfactant had been added was dispersed at 5000 rpm for 30 minutes using a high-speed homomixer to prepare a preliminary dispersion. The preliminary dispersion was then blended into mixed solution a1 to obtain a raw material solution, which was an aqueous dispersion. Next, this raw material liquid was passed through a commercially available filter ("Clear BM Filter, BM-03", manufactured by JNC Filter Corporation, filtration accuracy 3 μm) to prepare a coating liquid for forming the gas barrier layer (II) with a solid content of 10 mass %. The median diameter of droplets of the obtained coating liquid was 0.45 μm. The contents of the mineral oil and the acetylene glycol-based nonionic surfactant in the raw material liquid (the coating liquid) were 0.017 parts by mass of mineral oil and 0.011 parts by mass of acetylene glycol-based nonionic surfactant, respectively, per 100 parts by mass of the total mass (solid content) of PVA and EMA.The coating solution was applied to one side of an unstretched film that had been subjected to a water absorption treatment, and then dried. The ends of the unstretched film to which the coating solution had been applied and dried were held by clips of a tenter-type simultaneous biaxial stretching machine, and stretched 3.3 times in each of the MD and TD directions at 180°C. Thereafter, the film was heat-treated at 210°C for 4 seconds with a TD relaxation rate of 5%, and slowly cooled to room temperature to obtain a gas barrier laminate in which a 0.3 μm-thick gas barrier layer (II) was laminated on a 15 μm-thick plastic substrate (I) consisting of a single layer of metal-containing layer (M).

[0183] Examples 2 to 3 and 14 Gas barrier laminates were obtained in the same manner as in Example 1, except that the amounts and ratios of the mineral oil (A) and the acetylene glycol-based nonionic surfactant added were set to those shown in Table 1.

[0184] Example 4 Nylon 6 resin and master chip 2 were charged into extruder A so that the magnesium oxide content was 10% by mass, and melted in the cylinder at 270°C. Meanwhile, nylon 6 resin was charged into extruder B and melted in the cylinder at 270°C. The two resins melted in extruders A and B were overlapped in a die, and a two-layer sheet consisting of a metal-containing layer (M) and a resin layer (R) was extruded through a T-die and rapidly cooled by contacting it with a rotating drum cooled to 10°C, thereby obtaining a 150 μm-thick unstretched plastic substrate (I) film with an (M) / (R) ratio of 30 / 120 μm. A gas barrier laminate was obtained in the same manner as in Example 1, except that the unstretched plastic substrate (I) film was as shown in Table 1.

[0185] [Examples 5 and 6] A gas barrier laminate was obtained in the same manner as in Example 1, except that a film having the thickness of the unstretched plastic substrate (I) composed of the metal-containing layer (M) shown in Table 1 was obtained.

[0186] Examples 7, 8 and 9 Gas barrier laminates were obtained in the same manner as in Example 1, except that the magnesium oxide content of the metal-containing layer (M) was set as shown in Table 1.

[0187] Examples 10 and 11 Gas barrier laminates were obtained in the same manner as in Example 1, except that the thickness of the gas barrier layer (II) was set to the value shown in Table 1.

[0188] Examples 12 and 13 Gas barrier laminates were obtained in the same manner as in Example 1, except that the coating liquid composition for forming the gas barrier layer (II) was set so as to have the degree of neutralization of the polycarboxylic acid shown in Table 1.

[0189] Example 15 As shown in Table 1, a gas barrier laminate was obtained in the same manner as in Example 1, except that "SN Deformer 154S" manufactured by San Nopco Ltd. was used as the mineral oil (B).

[0190] Comparative Example 1 As shown in Table 2, a gas barrier laminate was obtained in the same manner as in Example 1, except that pure water was used instead of mixed liquid a2 when preparing the preliminary dispersion.

[0191] Comparative Example 2 As shown in Table 2, a gas barrier laminate was obtained in the same manner as in Example 1, except that a commercially available anionic surfactant "Nopco 1338" was used instead of the acetylene glycol-based nonionic surfactant "Olfine E1004."

[0192] Comparative Examples 3 and 4 Gas barrier laminates were obtained in the same manner as in Example 1, except that the amounts and ratios of the mineral oil and the acetylene glycol-based nonionic surfactant added were as shown in Table 2.

[0193] Comparative Example 5 As shown in Table 2, a gas barrier laminate was obtained in the same manner as in Comparative Example 1, except that the acetylene glycol surfactant was not added.

[0194] Comparative Example 6 As shown in Table 2, a gas barrier laminate was obtained in the same manner as in Example 1, except that the mineral oil was added directly to the mixed liquid a without pre-dispersion.

[0195] Comparative Example 7 A gas barrier laminate was obtained in the same manner as in Example 4, except that the magnesium oxide content of the metal-containing layer (M) was set as shown in Table 2 and pure water was used instead of mixed liquid a2 when preparing the preliminary dispersion.

[0196] [Comparative Example 8] A gas barrier laminate was obtained in the same manner as in Comparative Example 5, except that a film having a thickness of the unstretched plastic substrate (I) and a thickness of the metal-containing layer (M) shown in Table 2 was obtained.

[0197] Comparative Examples 9 and 10 Gas barrier laminates were obtained in the same manner as in Comparative Example 5, except that the thickness of the gas barrier layer (II) was set to the value shown in Table 2.

[0198] Comparative Examples 11 and 12 Gas barrier laminates were obtained in the same manner as in Comparative Example 5, except that the magnesium oxide content of the metal-containing layer (M) was set as shown in Table 2.

[0199] Comparative Example 13 As shown in Table 2, a gas barrier laminate was obtained in the same manner as in Comparative Example 5, except that the polycarboxylic acid was not neutralized.

[0200] Comparative Example 14 A gas barrier laminate was obtained in the same manner as in Comparative Example 5, except that the coating liquid composition for forming the gas barrier layer (II) was set so as to have the degree of neutralization of the polycarboxylic acid shown in Table 2.

[0201] Comparative Example 15 As shown in Table 2, a gas barrier laminate was obtained in the same manner as in Example 1, except that a vegetable oil "AIRASE 4655" manufactured by EVONIK was used instead of the mineral oil.

[0202] Comparative Example 16 As shown in Table 2, a gas barrier laminate was obtained in the same manner as in Example 1, except that mineral oil was not added to the coating liquid for forming the gas barrier layer (II).

[0203] Comparative Examples 17 and 18 Gas barrier laminates were obtained in the same manner as in Example 1, except that the amounts and ratios of the mineral oil and the acetylene glycol-based nonionic surfactant added were set to those shown in Table 2.

[0204] [Comparative Example 19] A gas barrier laminate was obtained in the same manner as in Comparative Example 5, except that a film was obtained having the thickness of the unstretched plastic substrate (I) consisting of the magnesium oxide content of the metal-containing layer (M), the thickness of the gas barrier layer (II), and the thickness of the metal-containing layer (M) shown in Table 2.

[0205] Test Example 1 The gas barrier laminates obtained in the examples and comparative examples were evaluated for the following properties. The results are shown in Tables 3 and 4.

[0206] (1) Thickness of each layer The obtained gas barrier laminate was left to stand for 2 hours or more in an environment of a temperature of 23°C and a humidity of 50% RH, and then the cross section of the film was observed with a scanning electron microscope (SEM) (magnification: 40,000 times) to measure the thickness of each layer. The thickness is measured at any three points using the above method, and the average value is shown.

[0207] (2) Median diameter of mineral oil droplets in coating solution for forming gas barrier layer (II) The coating solution for forming the gas barrier layer (II) immediately before being applied to an unstretched film was used as a measurement sample, and measurements were made using a laser diffraction particle size distribution analyzer (SALD-2300) manufactured by Shimadzu Corporation, and the median diameter (D50) was taken as the average particle diameter.

[0208] (3) Elastic Modulus and Hardness of Gas Barrier Layer (II) (Nanoindenter) The elastic modulus and hardness of the gas barrier layer (II) were measured using a nanoindenter (Triboindenter manufactured by Hysitron Inc.). A Berkovich indenter (triangular pyramidal indenter) (three-sided pyramidal structure, indenter interior angle of 142.35°, angle between the center line and the surface of 65.35°, indenter aspect ratio of 1:8) was used as the indenter. Specifically, the elastic modulus and hardness of the gas barrier layer (II) were measured by fixing the gas barrier laminate (gas barrier layer (II) on the upper surface) on a glass plate and using the nanoindenter at 25°C, with the indenter pressed 10 nm into the gas barrier layer (II). A single indentation measurement method was used as the measurement method. The modulus of elasticity and hardness are measured at any 10 points by the above method, and the average values ​​are shown.

[0209] (4) Oxygen permeability before elongation The gas barrier laminates obtained in each Example and Comparative Example were subjected to retort treatment at 120°C for 30 minutes, and then the oxygen permeability was measured using an oxygen permeability measuring device "OX-TRAN 2 / 22L" (sample size 10.8 cm x 10.8 cm) manufactured by Mocon Co., Ltd., under the following conditions: (a) a temperature of 20°C and a humidity of 90% RH, and (b) a temperature of 40°C and a humidity of 90% RH. The unit is ml / (m ２ ·day·MPa).

[0210] (5) Oxygen Permeability After Stretching The gas barrier laminate obtained in each Example and Comparative Example was subjected to retort treatment at 120°C for 30 minutes, and then stretched by 7% simultaneously in MD / TD using a biaxial stretching device for research and development "Karo IV" manufactured by BRUCKNER under an environment of a temperature of 35°C and a humidity of 50% RH. The gas barrier laminate was then measured for oxygen permeability using an oxygen permeability measuring device (OX-TRAN 2 / 22L) manufactured by Mocon (sample size 10.8 cm x 10.8 cm) under (a) an environment of a temperature of 20°C and a humidity of 90% RH and (b) an environment of a temperature of 40°C and a humidity of 90% RH. The unit is ml / (m ２ ·day·MPa).

[0211] (6) Evaluation of oxygen barrier properties after bending The gas barrier layer (II) of the gas barrier laminate obtained in each Example and Comparative Example was coated with a two-component curing polyurethane adhesive (DIC Graphics Corporation, LX-500 / KR-90) to a coating thickness of 4 μm (when dried) by gravure roll coating, and a 50 μm-thick unstretched polypropylene film (Mitsui Chemicals Tohcello Co., Ltd., CPP RXC-22) was dry-laminated as a sealant layer, followed by standing at 20°C and 40°C for 72 hours. In this way, gas barrier laminate films (test samples) were produced. The resulting laminate films were processed 10 times using a Gelbo Flex Tester (Tester Sangyo Co., Ltd.) at a temperature of 23°C and a humidity of 50% RH.

[0212] (6-1) Oxygen Permeability The laminate film treated 10 times with the Gelbo Flex Tester was subjected to a retort treatment at 120°C for 30 minutes, and then the oxygen permeability was measured using an oxygen permeability measuring device (OX-TRAN 2 / 22L) (sample size 10.8 cm x 10.8 cm) manufactured by Mocon Co., Ltd. under the following conditions: (a) a temperature of 20°C and a humidity of 90% RH, and (b) a temperature of 40°C and a humidity of 90% RH. The unit is ml / (m ２ ·day·MPa).

[0213] (6-2) Gas Barrier Layer Evaluation by Image Processing Using the laminate film processed 10 times with the Gelbo Flex Tester, a three-sided bag with external dimensions of 100 mm wide x 150 mm high was prepared with the sealant layer facing the inner surface. The bag was filled with the following preparation solution, and the remaining side was heat-sealed. The sealed three-sided bag was subjected to retort treatment at 120°C for 30 minutes, and the three-sided bag was photographed on a white sheet of paper. The blue areas in the three-sided bag after treatment indicate areas where oxygen had penetrated due to defects in the gas barrier layer (II). The photographs were converted to black and white using image processing software "GIMP 2.10" (saturation scale setting changed to 0.0), and the area ratios of the white and black areas were calculated. The threshold for evaluating the area ratio was set to 155 out of 255 gradations. The gas barrier layer defects after bending were evaluated using the following scoring criteria. When the area ratio of the blue portion (oxygen permeable portion) determined by image processing was less than 0.1%, it was marked "Good", when it was 0.1% or more and 0.3% or less it was marked "Fair", and when it was more than 0.3%, it was marked "Poor". The adjustment solution was prepared by placing 0.5 g of methylene blue, 1.0 g of thioglycolic acid, and 1000 ml of ion-exchanged water in a container and stirring.

[0214] (7) Aroma Retention Evaluation Three-sided bags with external dimensions of 100 mm height x 100 mm width were prepared using the laminated film obtained in the same manner as in "(6) Evaluation of oxygen barrier property after bending" above. 20 mL of a 3 wt% ethanol aqueous solution for aroma retention was filled into the bag, and the remaining side was heat-sealed and hermetically sealed. The three-sided bag filled with the 3 wt% ethanol aqueous solution was placed in an aluminum foil bag and vacuum-packaged. 100 cc of air captured with a syringe was injected into the vacuum-packaged aluminum bag and resealed. After storage for one month in an environment of 40°C temperature and 90% relative humidity, the concentration of ethanol leaked into the aluminum foil bag was measured using a Kitagawa-type gas sampler (manufactured by Komyo Rikagaku Kogyo Co., Ltd.). Aroma retention was evaluated according to the following scoring criteria: "Good" if the ethanol concentration was less than 0.05%, "Good" if it was 0.05% to 0.1%, and "Poor" if it was more than 0.1%.

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[0216]

[0217]

[0218]

[0219] As is clear from the results in Tables 3 and 4, the gas barrier laminates of Examples 1 to 15 were produced using a coating liquid containing a predetermined ratio of mineral oil and an acetylene glycol-based nonionic surfactant, and a preliminary dispersion in which the mineral oil was sufficiently dispersed. Therefore, the surface elastic modulus of the gas barrier layer (II) after retort treatment satisfied a specific range, and even after vacuum packaging, the laminates were able to exhibit excellent gas barrier properties in high-temperature and high-humidity environments, as well as excellent flex resistance, aroma retention, and the like.

[0220] In the gas barrier laminates of Comparative Examples 1 and 7, pure water was used instead of mixed liquid a2 when preparing the preliminary dispersion, and therefore the mineral oil and the acetylene glycol-based nonionic surfactant were not sufficiently dispersible, and the surface elastic modulus of the gas barrier layer (II) after retort treatment did not satisfy the specific range. As a result, gas barrier properties were not obtained in a high-temperature, high-humidity environment after vacuum packaging.

[0221] The gas barrier laminate of Comparative Example 2 contained an anionic surfactant instead of an acetylene glycol-based nonionic surfactant, and therefore the surface elastic modulus of the gas barrier layer (II) after retort treatment did not satisfy the specific range, and gas barrier properties were not obtained in a high-temperature, high-humidity environment after vacuum packaging.

[0222] The gas barrier laminates of Comparative Examples 5 to 6, 8 to 14, and 19 did not contain an acetylene glycol-based nonionic surfactant, and therefore the surface elastic modulus of the gas barrier layer (II) after retort treatment did not satisfy the specific range, and gas barrier properties were not obtained in a high-temperature, high-humidity environment after vacuum packaging.

[0223] The gas barrier laminates of Comparative Examples 15 and 16 did not contain mineral oil, and therefore the surface elastic modulus of the gas barrier layer (II) after retort treatment did not satisfy the specific range, and gas barrier properties were not obtained in a high-temperature, high-humidity environment after vacuum packaging.

[0224] On the other hand, in Comparative Examples 3 to 4 and 17 to 18, the gas barrier laminates were produced using a coating liquid in which the mineral oil and the acetylene glycol-based nonionic surfactant were not blended at a fixed ratio, and therefore the surface elastic modulus of the gas barrier layer (II) after retort treatment did not satisfy the specific range, and gas barrier properties were not obtained in a high-temperature, high-humidity environment after vacuum packaging.

Claims

1. A laminate comprising a plastic substrate (I) and a gas barrier layer (II) laminated on the plastic substrate, the laminate having a total thickness of 100 μm or less, characterized in that: (1) the plastic substrate (I) comprises a metal-containing layer containing at least one of a metal and a metal compound, and a resin component; (2) the total content of the metal and the metal compound in the metal-containing layer is 0.1 to 20 mass %; (3) the gas barrier layer (II) contains a polycarboxylic acid; (4) the metal-containing layer and the gas barrier layer are laminated so as to be in direct contact with each other; and (5) the composite elastic modulus of the surface of the gas barrier layer (II) after retorting the laminate at 120°C for 30 minutes is 9.0 to 12.5 GPa when measured by nanoindentation.

2. The gas barrier laminate according to claim 1, wherein the surface of the gas barrier layer (II) of the laminate is subjected to a retort treatment at 120°C for 30 minutes and then has a hardness of 0.7 to 1.3 GPa when measured by a nanoindentation method.

3. The laminate is subjected to a retort treatment at 120°C for 30 minutes, and then stretched by 7% simultaneously in both the MD and TD directions at a speed of 1.5% / s in an environment of 35°C and 50% RH. The oxygen permeability in an environment of 40°C and 90% RH is then 100 ml / (m ２ 2. The gas barrier laminate according to claim 1, wherein the gas barrier strength is 0.05 to 1.0 MPa (per day).

4. The gas barrier laminate according to claim 1, wherein the plastic substrate (I) is composed of a multilayer film including a metal-containing layer.

5. The gas barrier laminate according to claim 1, wherein the gas barrier layer (II) further contains a polyalcohol.

6. The gas barrier laminate according to claim 1, wherein the gas barrier layer (II) has a thickness of 0.05 to 5.00 μm, and the plastic substrate (I) has a thickness of 5 to 99.95 μm.

7. The gas barrier laminate according to claim 1, wherein the polycarboxylic acid comprises at least one of polyacrylic acid, an acrylic acid-maleic acid copolymer, and an olefin-maleic acid copolymer.

8. The gas barrier laminate according to claim 1, wherein the resin component contained in the metal-containing layer comprises one or more types of thermoplastic resin, and the content of the resin component in the metal-containing layer is 99.9 to 80 mass %.

9. The gas barrier laminate according to claim 1, wherein the plastic substrate (I) is composed of one or more metal-containing layers and one or more other resin-containing layers, and the ratio [(Rt) / (Mt)] of the total thickness (Mt) of the metal-containing layers (M) to the total thickness (Rt) of the other resin-containing layers (R) is 1 / 10 to 10 / 1.

10. The gas barrier laminate according to claim 1, wherein the metal compound is at least one of lithium carbonate, sodium hydrogen carbonate, magnesium oxide, magnesium carbonate, magnesium hydroxide, magnesium acetate, calcium oxide, calcium carbonate, calcium hydroxide, calcium chloride, calcium phosphate, calcium sulfate, calcium acetate, zinc acetate, zinc oxide and zinc carbonate.

11. The gas barrier laminate according to claim 1, wherein the gas barrier layer (II) contains an olefin-maleic acid copolymer, and the content of maleic acid units in the olefin-maleic acid copolymer is 5 mol % or more.

12. The gas barrier laminate according to claim 1, wherein the metal or metal compound is in the form of a powder having an average particle size of 0.005 to 5.0 μm.

13. A packaging bag comprising the gas barrier laminate according to any one of claims 1 to 12.

14. A vacuum-packed product in which at least a solid material is contained and sealed in the packaging bag according to claim 13.

15. A method for producing a gas barrier laminate, comprising: (1) preparing a raw material liquid containing polycarboxylic acid, mineral oil, and an acetylene glycol-based nonionic surfactant, in which the mass ratio of the mineral oil to the acetylene glycol-based nonionic surfactant is 80 / 20 to 40 / 60; and (2) applying the raw material liquid as a coating liquid for forming a gas barrier layer (II) onto at least a surface of a metal-containing layer of a plastic substrate (I) including a metal-containing layer that contains at least one of a metal and a metal compound, and a resin component.

16. The manufacturing method according to claim 15, further comprising a step of preparing a coating liquid for forming a gas barrier layer (II) by passing the raw material liquid through a filter having a filtration accuracy of 1.0 to 10.0 μm prior to applying the raw material liquid to the plastic substrate (I).

17. The method according to claim 16, wherein the median diameter of the coating liquid for forming the gas barrier layer (II) after passing through the filter is 0.1 to 0.6 μm.

18. A method for producing a gas barrier laminate according to claim 15, further comprising a step of subjecting the laminate coated with the raw material liquid to simultaneous biaxial stretching or sequential biaxial stretching after the raw material liquid has been applied to the plastic substrate (I).

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