Gas barrier layer forming composition, gas barrier film, laminate, and packaging bag

Abstract

To provide a gas barrier layer-forming composition capable of forming a gas barrier layer less prone to deterioration of gas barrier properties after heating.SOLUTION: A gas barrier layer-forming composition contains an aqueous polyurethane resin (A) containing an acid group-containing polyurethane resin, and a water-soluble polymer (B). The aqueous polyurethane resin (A) is free of polyurethane resin particles with a circle equivalent diameter exceeding 20 μm. A mass ratio between the aqueous polyurethane resin (A) and the water-soluble polymer (B) in a solid content (aqueous polyurethane resin (A) / water-soluble polymer (B)) is 85 / 15-10 / 90.SELECTED DRAWING: None

Description

Technical Field

[0001] The present disclosure relates to a composition for forming a gas barrier layer, a gas barrier film, a laminate, and a packaging bag. Background Art

[0002] For packaging bags used for packaging foods, pharmaceuticals and the like, gas barrier properties that block the intrusion of water vapor, oxygen and other gases that deteriorate contents are required in order to suppress deterioration and putrefaction of the contents and maintain their functions and properties. For this reason, gas barrier films have conventionally been used in these packaging bags.

[0003] A gas barrier film generally includes a gas barrier layer on one surface side of a resin substrate, and the gas barrier layer is formed by applying a composition for forming a gas barrier layer capable of imparting gas barrier properties to one surface side of the resin substrate and curing the composition.

[0004] Various types of such gas barrier films have been developed conventionally.

[0005] For example, Patent Document 1 below discloses a gas barrier film in which a gas barrier layer is formed by using, as the composition for forming a gas barrier layer, a composition containing a solid content consisting of a polyurethane resin, a water-soluble polymer, an inorganic layered mineral, and a silane coupling agent. Prior Art Documents Patent Documents

[0006] Patent Document 1 Japanese Unexamined Patent Application Publication No. 2017-222151 Summary of the Invention Problems to be Solved by the Invention

[0007] However, the gas barrier film described in Patent Document 1 had the problem that its gas barrier properties may decrease after heat treatment.

[0008] This disclosure has been made in view of the problems of the prior art described above, and aims to provide a gas barrier layer forming composition capable of forming a gas barrier layer that can suppress the decrease in gas barrier properties after heat treatment, a gas barrier film, a laminate, and a packaging bag using the same. [Means for solving the problem]

[0009] As a result of extensive research to solve the above problems, the inventors of the present invention have found that the performance of a gas barrier film equipped with a gas barrier layer using polyurethane resin can vary depending on the polyurethane resin used. In particular, it has been confirmed that when heat sterilization such as retort processing is performed, the deterioration of gas barrier properties due to heat treatment can be significant. As a result of diligent research to find a method for forming a gas barrier layer that exhibits stable gas barrier properties even after heat treatment, the inventors of the present invention have found that the above problems can be solved by the following invention.

[0010] In other words, the present disclosure provides a gas barrier layer forming composition comprising an aqueous polyurethane resin (A) containing an acid group-containing polyurethane resin and a water-soluble polymer (B), wherein the aqueous polyurethane resin (A) does not contain polyurethane resin particles with an equivalent circle diameter exceeding 20 μm, and the mass ratio of solid content between the aqueous polyurethane resin (A) and the water-soluble polymer (B) (aqueous polyurethane resin (A) / water-soluble polymer (B)) is 80 / 20 to 65 / 35.

[0011] The inventors have found that when a gas barrier layer is formed using a gas barrier layer-forming composition containing coarse polyurethane resin particles, voids and cracks tend to occur around the coarse particles, and these become more pronounced after heat treatment. Furthermore, when a gas barrier layer is formed on a resin substrate made of polyolefin film, the thermal shrinkage of the polyolefin film is greater than that of conventionally used polyester film. As a result, voids and cracks tend to occur more easily around the coarse particles in the gas barrier layer due to the thermal shrinkage of the resin substrate. When these voids and cracks occur in the gas barrier layer, the gas barrier properties decrease. The inventors studied the effect on gas barrier properties by removing coarse particles from aqueous polyurethane resin (A) using filters of various sizes. They found that by removing polyurethane resin particles with an equivalent circle diameter exceeding 20 μm, it is possible to form a gas barrier layer that can suppress the decrease in gas barrier properties after heat treatment, even when a polyolefin film is used as the resin substrate. In other words, the gas barrier layer-forming composition of the present disclosure having the above configuration can form a gas barrier layer that can suppress the decrease in gas barrier properties after heat treatment.

[0012] The above gas barrier layer forming composition may further contain a silane coupling agent (C). By including a silane coupling agent (C) in the gas barrier layer forming composition, the resulting gas barrier layer can more effectively suppress the decrease in gas barrier properties after heat treatment and can also improve the lamination strength to the resin substrate.

[0013] This disclosure also provides a gas barrier film comprising a resin substrate and a gas barrier layer formed on one side of the resin substrate using the gas barrier layer forming composition of this disclosure. The gas barrier film makes it possible to suppress the decrease in gas barrier properties after heat treatment.

[0014] The above-mentioned gas barrier film may have a gas barrier layer thickness of 0.1 to 10 μm in areas where polyurethane resin particles with an equivalent circular diameter exceeding 10 μm are not present.

[0015] The above-described gas barrier film may further include an inorganic oxide layer containing an inorganic oxide between the resin substrate and the gas barrier layer. By including the inorganic oxide layer, the gas barrier properties of the gas barrier film can be further improved.

[0016] In the above-described gas barrier film, the resin substrate may be a polyolefin film. The polyolefin film may also be a polyethylene film.

[0017] The disclosure also provides a laminate comprising the gas barrier film described above and a sealant layer laminated on the gas barrier film (which maintains high gas barrier properties even after heat treatment).

[0018] In the above-described laminate, the resin substrate and the sealant layer in the gas barrier film may both be polyethylene films, or they may both be polypropylene films. By using the same material for the resin substrate and the sealant layer, the recyclability of the laminate and the packaging bag using it can be further improved.

[0019] The disclosure also provides a packaging bag formed by using the laminate of the disclosure and joining the sealant layers together (which maintains high gas barrier properties even after heat treatment). [Effects of the Invention]

[0020] According to this disclosure, it is possible to provide a gas barrier layer forming composition capable of forming a gas barrier layer that can suppress the decrease in gas barrier properties after heat treatment, as well as a gas barrier film, laminate, and packaging bag using the same. [Brief explanation of the drawing]

[0021] [Figure 1] It is a schematic cross-sectional view showing one embodiment of the gas barrier film of the present disclosure. [Figure 2] It is a schematic cross-sectional view showing one embodiment of the laminate of the present disclosure. MODE FOR CARRYING OUT THE INVENTION

[0022] Hereinafter, embodiments of the present disclosure will be described in detail.

[0023] <Composition for Forming Gas Barrier Layer> The composition for forming a gas barrier layer contains an aqueous polyurethane resin (A) including an acid group-containing polyurethane resin, and a water-soluble polymer (B). Here, the aqueous polyurethane resin (A) does not contain polyurethane resin particles having an equivalent circle diameter exceeding 20 µm. Further, the mass ratio of the solid content of the aqueous polyurethane resin (A) to the water-soluble polymer (B) (aqueous polyurethane resin (A) / water-soluble polymer (B)) is from 85 / 15 to 10 / 90. The composition for forming a gas barrier layer may further contain a silane coupling agent (C). Hereinafter, each component constituting the composition for forming a gas barrier layer will be described in detail.

[0024] (Aqueous Polyurethane Resin (A)) The aqueous polyurethane resin (A) includes an acid group-containing polyurethane resin having an acid group. The aqueous polyurethane resin (A) is used for imparting flexibility and gas barrier properties, particularly oxygen barrier properties, to the gas barrier layer.

[0025] Since the acid group-containing polyurethane resin constituting the aqueous polyurethane resin (A) has an acid group, it has anionic properties and self-emulsifying properties, and is also referred to as an anionic self-emulsifying polyurethane resin. Examples of the acid group include a carboxyl group, a sulfonic acid group and the like. The acid group can usually be neutralized with a neutralizing agent (base), and may form a salt with the base. The acid group may be located at the terminal or in the side chain of the acid group-containing polyurethane resin, but is preferably located at least in the side chain.

[0026] The aqueous polyurethane resin (A) may further contain a polyamine compound. The polyamine compound functions as a crosslinking agent. In the aqueous polyurethane resin (A), the gas barrier properties can be improved by bonding the acid groups of the acid group-containing polyurethane resin with the polyamine compound as a crosslinking agent. In this case, the acid groups of the acid group-containing polyurethane resin are assumed to be capable of bonding with the amino groups (primary amino groups, secondary amino groups, tertiary amino groups, etc.) of the polyamine compound. The bond between the acid groups of the acid group-containing polyurethane resin and the polyamine compound may be an ionic bond (for example, an ionic bond between a carboxyl group and a tertiary amino group) or a covalent bond (for example, an amide bond).

[0027] The acid value of the acid group-containing polyurethane resin can be selected within the range in which the acid group-containing polyurethane resin is water-dispersible, but is usually 5 to 100 mg KOH / g, preferably 10 to 70 mg KOH / g, and more preferably 15 to 60 mg KOH / g. If the acid value of the acid group-containing polyurethane resin is above the lower limit of the above range, the water dispersibility of the acid group-containing polyurethane resin will be good, and the uniform dispersion of the aqueous polyurethane resin with other materials and the dispersion stability of the gas barrier layer forming composition can be improved. If the acid value of the acid group-containing polyurethane resin is below the upper limit of the above range, the water resistance and gas barrier properties of the gas barrier layer can be improved. The acid value of the acid group-containing polyurethane resin is measured by a method in accordance with JIS K0070.

[0028] From the viewpoint of gas barrier properties, the total concentration of urethane groups and urea groups in the acid group-containing polyurethane resin is preferably 15% by mass or more, and more preferably 20 to 60% by mass. If the total concentration of urethane groups and urea groups is above the lower limit, the gas barrier properties of the gas barrier layer tend to improve. If the total concentration of urethane groups and urea groups is below the upper limit of the above range, the flexibility of the gas barrier layer tend to improve.

[0029] The urethane group concentration refers to the ratio of the molecular weight of the urethane group (59 g / equivalent) to the molecular weight of the repeating structural units of the polyurethane resin. The urea group concentration refers to the ratio of the molecular weight of the urea group (primary amino group: 58 g / equivalent, secondary amino group: 57 g / equivalent) to the molecular weight of the repeating structural units of the polyurethane resin. When a mixture of two or more acid group-containing polyurethane resins is used, the urethane group concentration and urea group concentration can be calculated based on the base of the reaction components, i.e., the usage ratio of each component.

[0030] Acid group-containing polyurethane resins may typically have at least rigid units (units composed of hydrocarbon rings) and short-chain units (for example, units composed of hydrocarbon chains). That is, the constituent units of acid group-containing polyurethane resins may typically contain hydrocarbon rings (at least one of aromatic and non-aromatic hydrocarbon rings) derived from polyisocyanate components, polyhydroxy acid components, polyol components, and chain extension components (in particular, at least polyisocyanate components).

[0031] The proportion of units composed of hydrocarbon rings in the constituent units of acid group-containing polyurethane resin is typically 10 to 70% by mass, preferably 15 to 65% by mass, and more preferably 20 to 60% by mass, relative to the total of all constituent units. When the proportion of units composed of hydrocarbon rings is above the lower limit of the above range, the gas barrier properties of the gas barrier layer tend to improve. When the proportion of units composed of hydrocarbon rings is below the upper limit of the above range, the flexibility of the gas barrier layer tend to improve.

[0032] The number-average molecular weight of the acid-group-containing polyurethane resin can be appropriately selected, but is preferably 800 to 1,000,000, more preferably 800 to 200,000, and even more preferably 800 to 100,000. If the number-average molecular weight of the acid-group-containing polyurethane resin is below the upper limit of the above range, it is easier to suppress the increase in viscosity of the gas barrier layer-forming composition. If the number-average molecular weight of the acid-group-containing polyurethane resin is above the lower limit of the above range, the gas barrier properties of the gas barrier layer are easily improved. The number-average molecular weight of the acid-group-containing polyurethane resin is a value on a standard polystyrene basis measured by gel permeation chromatography (GPC).

[0033] The acid group-containing polyurethane resin may be crystalline from the viewpoint of improving gas barrier properties. The glass transition temperature of the acid group-containing polyurethane resin is preferably 100°C or higher, more preferably 110°C or higher, and even more preferably 120°C or higher. When the glass transition temperature of the acid group-containing polyurethane resin is 100°C or higher, the gas barrier properties of the gas barrier layer tend to improve. The glass transition temperature of the acid group-containing polyurethane resin is typically 200°C or lower, more preferably 180°C or lower, and even more preferably 150°C or lower. It is substantially unlikely that the glass transition temperature of an acid group-containing polyurethane resin that satisfies the preferred ranges of each of the above items will be higher than the above upper limits. Therefore, the glass transition temperature of the acid group-containing polyurethane resin is preferably 100 to 200°C, more preferably 110 to 180°C, and even more preferably 120 to 150°C. The glass transition temperature of the acid group-containing polyurethane resin is measured by differential scanning calorimetry (DSC).

[0034] The polyamine compound constituting the aqueous polyurethane resin (A) is a compound having two or more basic nitrogen atoms. The basic nitrogen atoms are nitrogen atoms that can bond with the acid group of the acid group-containing polyurethane resin, and examples include nitrogen atoms in amino groups such as primary amino groups, secondary amino groups, and tertiary amino groups.

[0035] The polyamine compound is not particularly limited as long as it can bond with the acid group of the acid group-containing polyurethane resin and improve the gas barrier properties, and various compounds having two or more basic nitrogen atoms can be used. Preferably, the polyamine compound has two or more amino groups selected from the group consisting of primary amino groups, secondary amino groups, and tertiary amino groups.

[0036] Specific examples of polyamine compounds include alkylenediamines, polyalkylene polyamines, and silicon compounds having multiple basic nitrogen atoms. Examples of alkylenediamines include alkylenediamines having 2 to 10 carbon atoms, such as ethylenediamine, 1,2-propylenediamine, 1,3-propylenediamine, 1,4-butanediamine, and 1,6-hexamethylenediamine. Examples of polyalkylene polyamines include tetraalkylene polyamines. Examples of silicon compounds having multiple basic nitrogen atoms (including nitrogen atoms such as amino groups) include silane coupling agents having multiple basic nitrogen atoms, such as 2-[N-(2-aminoethyl)amino]ethyltrimethoxysilane and 3-[N-(2-aminoethyl)amino]propyltrimethoxysilane. These can be used individually or in combination of two or more.

[0037] When the aqueous polyurethane resin (A) contains a polyamine compound, the amount of polyamine compound is preferably such that the molar ratio (acid group / basic nitrogen atom) of the acid group-containing polyurethane resin to the basic nitrogen atoms of the polyamine compound is 10 / 1 to 0.1 / 1, and more preferably 5 / 1 to 0.2 / 1. If the acid group / basic nitrogen atom ratio is within the above range, the crosslinking reaction between the acid group-containing polyurethane and the polyamine compound will occur appropriately, and the oxygen barrier properties of the gas barrier layer can be further improved.

[0038] Aqueous polyurethane resin (A) is usually used in the form of an aqueous dispersion. Examples of aqueous media include water, water-soluble or hydrophilic organic solvents, or mixtures thereof. Examples of water-soluble or hydrophilic organic solvents include alcohols such as methanol, ethanol, and isopropanol; ketones such as acetone and methyl ethyl ketone; ethers such as tetrahydrofuran; cellosolves; carbitols; and nitriles such as acetonitrile.

[0039] As the aqueous medium, water or a material mainly composed of water is preferred. The water content in the aqueous medium is preferably 70% by mass or more, and more preferably 80% by mass or more. The aqueous medium may or may not contain a neutralizing agent (base) to neutralize the acid groups of the acid group-containing polyurethane resin. Usually, a neutralizing agent is included.

[0040] The aqueous polyurethane resin (A) does not contain polyurethane resin particles with an equivalent circle diameter exceeding 20 μm. The absence of polyurethane resin particles with an equivalent circle diameter exceeding 20 μm can be confirmed by the following method. Specifically, the particle size distribution of the equivalent circle diameter of the aqueous polyurethane resin (A) is measured using the following measuring equipment and conditions. From the results of measuring 300 particles, the maximum equivalent circle diameter of the polyurethane resin particles contained in the aqueous polyurethane resin (A) is determined. If the maximum equivalent circle diameter is 20 μm or less, it is determined that the aqueous polyurethane resin (A) does not contain polyurethane resin particles with an equivalent circle diameter exceeding 20 μm. Therefore, the absence of polyurethane resin particles with an equivalent circle diameter exceeding 20 μm in the aqueous polyurethane resin (A) is equivalent to the maximum equivalent circle diameter of the polyurethane resin particles in the aqueous polyurethane resin (A) measured by the above method being 20 μm or less. Furthermore, from the particle size distribution of 300 particles measured using this measurement method, the average equivalent circle diameter of the polyurethane resin particles and the number of polyurethane resin particles with an equivalent circle diameter greater than or equal to a predetermined value can be determined.

[0041] (Measurement equipment and conditions) Equipment used: Particle shape image analyzer (manufactured by Seishin Corporation, product name: PITA-04) Analysis principle: Dynamic image analysis method Particle size measurement range: 1 to 1000 μm Particle size distribution: Volume- and area-equivalent particle size distribution

[0042] An aqueous polyurethane resin (A) that does not contain polyurethane resin particles with an equivalent circular diameter exceeding 20 μm can be obtained, for example, by passing the aqueous polyurethane resin (A) through a filter of a predetermined size (mesh opening) to remove coarse particles.

[0043] The maximum equivalent diameter of polyurethane resin particles in the aqueous polyurethane resin (A) measured by the above method is 20 μm or less, but from the viewpoint of further suppressing the decrease in the gas barrier properties of the gas barrier layer after heat treatment, it may be 15 μm or less, or 10 μm or less.

[0044] The average equivalent circle diameter of the polyurethane resin particles in the aqueous polyurethane resin (A) measured by the above method may be 15 μm or less, or 10 μm or less, from the viewpoint of further suppressing the decrease in the gas barrier properties of the gas barrier layer after heat treatment.

[0045] The number (percentage) of polyurethane resin particles with an equivalent circle diameter of 10 μm or more in the aqueous polyurethane resin (A) measured by the above method may be 9 / 300 (3%) or less, 5 / 300 (1.7%) or less, or 0 / 300 (0%), from the viewpoint of further suppressing the decrease in the gas barrier properties of the gas barrier layer after heat treatment.

[0046] (Water-soluble polymer (B)) Water-soluble polymers refer to polymers that can dissolve in water. Here, dissolution refers to a state in which the polymer, which is the solute, is dispersed at the molecular chain level in the solvent, water, forming a homogeneous system. More specifically, it refers to a state in which the intermolecular forces with water molecules become stronger than the intermolecular forces between the polymer chains, untangling the polymer chains and allowing them to be uniformly dispersed in water. Water-soluble polymers (B) are used in particular to improve the flexibility of gas barrier layers and to suppress the deterioration of gas barrier properties due to post-processing.

[0047] Specific examples of water-soluble polymers (B) include, for example, polyvinyl alcohol resins such as polyvinyl alcohol polymers and their derivatives; vinyl polymers such as polyvinylpyrrolidone, polyacrylic acid, polymethacrylic acid or their esters, salts and copolymers thereof, polyhydroxyethyl methacrylate and its copolymers; cellulose derivatives such as carboxymethylcellulose and hydroxyethylcellulose; starches such as oxidized starch, etherified starch, and dextrin; copolymer polyesters having acid components containing polar groups such as sulfoisophthalic acid; water-soluble urethane polymers; and functional group-modified polymers obtained by modifying the functional groups (carboxyl groups, etc.) of these various polymers. Examples of derivatives of polyvinyl alcohol polymers include graft polymers obtained by graft polymerization of monomers onto the side chains of polyvinyl alcohol.

[0048] The water-soluble polymer (B) preferably has a degree of polymerization of 200 or higher, considering the film aggregation strength. The water-soluble polymer (B) contained in the gas barrier layer forming composition may be one type or two or more types.

[0049] The water-soluble polymer (B) preferably contains at least one polyvinyl alcohol resin selected from the group consisting of polyvinyl alcohol polymers and their derivatives, from the viewpoint of achieving both gas barrier properties and flexibility in the gas barrier layer, and is particularly preferably a polyvinyl alcohol resin with a saponification degree of 95% or more and a degree of polymerization of 300 or more. The degree of polymerization of the polyvinyl alcohol resin is preferably 300 to 2400, and particularly preferably 450 to 2000.

[0050] The higher the degree of saponification and polymerization of polyvinyl alcohol resin, the lower its moisture absorption and swelling properties become, and the higher its gas barrier properties. When the degree of saponification of polyvinyl alcohol resin is 95% or higher, sufficient gas barrier properties are easily obtained. When the degree of polymerization of polyvinyl alcohol resin is 300 or higher, it is easier to suppress the decrease in gas barrier properties and film cohesive strength. When the degree of polymerization of polyvinyl alcohol resin is 2000 or lower, it is easier to suppress the increase in viscosity of the gas barrier layer forming composition, it is easier to mix uniformly with other components, and it is easier to suppress the decrease in gas barrier properties and adhesion strength.

[0051] (Silane coupling agent (C)) As the silane coupling agent (C), commonly used compounds can be used, such as compounds having an alkoxy group bonded to a silicon atom and an organic reactive group.

[0052] Examples of silane coupling agents (C) include compounds represented by RSiX3 (where R is an organic reactive group and X is an alkoxy group). Examples of organic reactive groups include those having amino groups, (meth)acrylic groups, epoxy groups, vinyl groups, mercapto groups, isocyanate groups, isocyanurate groups, etc. (Meth)acrylic groups can represent both acrylic and methacrylic groups. Examples of alkoxy groups include methoxy groups and ethoxy groups.

[0053] Examples of silane coupling agents (C) include vinyl trimethoxysilane and vinyl triethoxysilane as silane coupling agents having a vinyl group. Examples of silane coupling agents having an epoxy group include 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, 3-glycidoxypropyltrimethoxysilane, 3-glycidoxypropyltriethoxysilane, 3-glycidoxypropylmethyldimethoxysilane, and 3-glycidoxypropylethyldiethoxysilane. Examples of silane coupling agents having an amino group include 3-aminopropyltrimethoxysilane and 3-aminopropyltriethoxysilane. Examples of silane coupling agents having a mercapto group include 3-mercaptopropyltrimethoxysilane and 3-mercaptopropylmethyldimethoxysilane. Examples of silane coupling agents having a (meth)acrylic group include 3-acryloxypropyltrimethoxysilane. Examples of silane coupling agents having an isocyanate group include 3-isocyanatetopropyltriethoxysilane. Examples of silane coupling agents containing an isocyanurate group include tris-(trimethoxysilylpropyl)isocyanurate. These silane coupling agents may be used individually or in combination of two or more.

[0054] As the silane coupling agent (C), one in which the organic reactive group has reactivity with the components in the gas barrier layer forming composition is preferably used. As the silane coupling agent (C), one having an epoxy group is preferred. Since the epoxy group has good reactivity with the hydroxyl group of the aqueous polyurethane resin (A) or the water-soluble polymer (B), the gas barrier properties of the gas barrier layer can be further improved.

[0055] (Other ingredients) The gas barrier layer forming composition may contain other components besides those mentioned above, as long as they do not impair the gas barrier properties of the gas barrier layer. Examples of other components include additives such as antioxidants, weathering agents, heat stabilizers, lubricants, crystal nucleating agents, ultraviolet absorbers, plasticizers, antistatic agents, colorants, fillers, and surfactants.

[0056] From the viewpoint of further suppressing the decrease in gas barrier properties after heat treatment, the gas barrier layer-forming composition preferably does not contain inorganic layered minerals. Even if the gas barrier layer-forming composition contains inorganic layered minerals, the content thereof is preferably less than 2% by mass based on the total solid content of the gas barrier layer-forming composition.

[0057] Examples of inorganic layered minerals include hydrated silicates such as phyllosilicate minerals. Specifically, hydrated silicates include kaolinite clay minerals such as halloysite, kaolinite, and endelite; antigorite clay minerals such as antigorite and chrysotile; smectite clay minerals such as montmorillonite and beidelite; vermiculite clay minerals such as vermiculite; and micas such as synthetic mica, muscovite, and phlogopite.

[0058] (Content of each component) In the gas barrier layer forming composition, the mass ratio of the aqueous polyurethane resin (A) to the water-soluble polymer (B) in terms of solid content (aqueous polyurethane resin (A) / water-soluble polymer (B)) is 85 / 15 to 10 / 90, preferably 75 / 25 to 20 / 80, and particularly preferably 70 / 30 to 25 / 75.

[0059] When the solid content mass ratio of aqueous polyurethane resin (A) to water-soluble polymer (B) is within the above range, the gas barrier layer-forming composition can be applied evenly, forming a gas barrier layer that is excellent in gas barrier properties and flexibility, and that suppresses the decrease in gas barrier properties after heat treatment. If the content of aqueous polyurethane resin (A) is higher than the solid content mass ratio of aqueous polyurethane resin (A) to water-soluble polymer (B) of 85 / 15, unevenness may occur during coating. Unevenness during coating can lead to deterioration of appearance and a decrease in gas barrier properties. If the content of aqueous polyurethane resin (A) is lower than the ratio of aqueous polyurethane resin (A) to water-soluble polymer (B) of 10 / 90, the oxygen barrier properties may be insufficient.

[0060] The content (solids) of the silane coupling agent (C) in the gas barrier layer forming composition is preferably 0.5% by mass or more and 30% by mass or less, more preferably 1% by mass or more and 25% by mass or less, and particularly preferably 3% by mass or more and 20% by mass or less, based on the total amount of solids in the gas barrier layer forming composition. By having the content of the silane coupling agent (C) within the above range, the cohesive force and gas barrier properties of the gas barrier layer can be sufficiently enhanced while maintaining the flexibility of the gas barrier layer formed from the gas barrier layer forming composition.

[0061] In the gas barrier layer forming composition, the total content (solids) of aqueous polyurethane resin (A), water-soluble polymer (B), and silane coupling agent (C) is preferably 85% by mass or more, more preferably 90% by mass or more, and particularly preferably 95% by mass or more, based on the total solids content in the gas barrier layer forming composition. The upper limit of this total content is not particularly limited and may be 100% by mass.

[0062] <Gas barrier film> Figure 1 is a schematic cross-sectional view showing one embodiment of the gas barrier film of the present disclosure. In Figure 1, the gas barrier film 10 comprises a resin substrate 1 and a gas barrier layer 4 provided on one side of the resin substrate 1, and between the resin substrate 1 and the gas barrier layer 4, a base layer 2 and an inorganic oxide layer 3 are provided sequentially from the resin substrate 1 side. The gas barrier layer 4 is formed using the gas barrier layer forming composition described above.

[0063] The resin substrate 1, underlayer 2, inorganic oxide layer 3, and gas barrier layer 4 will be described in detail below.

[0064] (Resin base material) The resin substrate 1 is a substrate that serves as a support for the gas barrier layer 4 and contains a resin. Examples of resins include polyolefin resins, polyester resins, polyamide resins, polyether resins, acrylic resins, polyimide resins, epoxy resins, and natural polymer compounds (such as cellulose acetate). These may be used individually or as a mixture of two or more.

[0065] In particular, polyolefin resins are preferred from a recycling standpoint. Examples of polyolefin resins include polyethylene and polypropylene, but polypropylene is preferred from the viewpoint of retort treatment resistance. Here, polypropylene may be homopolypropylene or propylene copolymer, but from the viewpoint of oxygen barrier properties, it is more preferable that the polypropylene constituting at least the surface layer on the gas barrier layer 4 side of the resin substrate 1 is a polypropylene copolymer.

[0066] The resin substrate 1 may be a stretched film or an unstretched film, but from the viewpoint of oxygen barrier properties, a stretched film is preferred. Here, examples of stretched films include uniaxially oriented films and biaxially oriented films, but biaxially oriented films are preferred because they improve heat resistance.

[0067] The thickness of the resin substrate 1 is not particularly limited, but for example, it should be between 10 μm and 0.1 mm.

[0068] The resin substrate 1 may contain additives such as antistatic agents, ultraviolet absorbers, plasticizers, and lubricants, as needed.

[0069] (base layer) The base layer 2 is a layer designed to further improve the adhesion between the resin substrate 1 and the inorganic oxide layer 3, and is sandwiched between the resin substrate 1 and the inorganic oxide layer 3.

[0070] The material constituting the base layer 2 is not particularly limited as long as it can improve the adhesion between the resin substrate 1 and the inorganic oxide layer 3, but such materials include reaction products of organosilane or organometallic compounds, polyol compounds, and isocyanate compounds. In other words, the base layer 2 can also be said to be a urethane adhesive layer. The organosilane is, for example, a trifunctional organosilane or a hydrolysate of a trifunctional organosilane. The organometallic compound is, for example, a metal alkoxide or a hydrolysate of a metal alkoxide. The metal elements contained in the organometallic compound are, for example, Al, Ti, Zr, etc. The hydrolysate of the organosilane and the hydrolysate of the metal alkoxide each only need to have at least one hydroxyl group. From the viewpoint of transparency, the polyol compound is preferably an acrylic polyol. The isocyanate compound mainly functions as a crosslinking agent or a curing agent. The polyol compound and the isocyanate compound may be monomers or polymers.

[0071] The thickness of the base layer 2 is not particularly limited as long as it is a thickness that can improve the adhesion between the resin substrate 1 and the inorganic oxide layer 3, but is preferably 30 nm or more. In this case, it is easier to obtain good adhesion between the resin substrate 1 and the inorganic oxide layer 3 compared to when the thickness of the base layer 2 is less than 30 nm. In addition, the durability of the base layer 2 is further improved. The thickness of the base layer 2 is preferably 30 nm or more, more preferably 35 nm or more, and even more preferably 40 nm or more. By increasing the thickness of the base layer 2, the decrease in water vapor barrier properties when external forces such as stretching are applied can be further suppressed. The thickness of the base layer 2 is preferably less than 200 nm. In this case, it is easier to prevent cracks from forming in the base layer 2 compared to when the thickness of the base layer 2 is 200 nm or more.

[0072] (Inorganic oxide layer) The inorganic oxide layer 3 is a layer containing an inorganic oxide. The gas barrier film 10 can have better water vapor barrier properties by having the inorganic oxide layer 3.

[0073] Examples of inorganic oxides include silicon oxides (SiOx) and metal oxides. The metal constituting the metal oxide can be at least one atom selected from the group consisting of Al, Mg, Sn, Ti, and In. From the viewpoint of water vapor barrier properties, SiOx is used as an inorganic oxide. x or AlO x This is preferable. Among the inorganic oxides, SiO x This is preferable. In this case, the gas barrier film 10 can have better water vapor barrier properties.

[0074] The inorganic oxide layer 3 may consist of a single layer or multiple layers.

[0075] The thickness of the inorganic oxide layer 3 is not particularly limited, but it is preferably between 10 nm and 100 nm. In this case, the water vapor barrier properties of the gas barrier film 10 are more easily improved compared to when the thickness of the inorganic oxide layer 3 is less than 10 nm. Also, compared to when the thickness of the inorganic oxide layer 3 exceeds 100 nm, cracks due to increased internal stress are less likely to occur, and the decrease in water vapor barrier properties can be more suppressed.

[0076] The thickness of the inorganic oxide layer 3 is more preferably 10 nm or more and 100 nm or less.

[0077] (Gas barrier layer) The gas barrier layer 4 is a layer formed using the gas barrier layer forming composition described above. The gas barrier layer 4 may also be composed of a cured body of the gas barrier layer forming composition.

[0078] The thickness of the gas barrier layer 4 is not particularly limited, but the thickness measured in areas where polyurethane resin particles with an equivalent circle diameter exceeding 10 μm are not present is preferably 0.1 to 10 μm, more preferably 0.1 to 1 μm, and even more preferably 0.1 to 0.5 μm.

[0079] When the thickness of the gas barrier layer 4 is 0.1 μm or more, the gas barrier properties of the gas barrier layer 4 can be improved compared to when the thickness is less than 0.1 μm. On the other hand, when the thickness of the gas barrier layer 4 is 10 μm or less, the flexibility of the gas barrier layer 4 can be improved compared to when the thickness exceeds 10 μm.

[0080] <Method for manufacturing gas barrier film> Next, a method for manufacturing the gas barrier film 10 will be described.

[0081] First, prepare the resin base material 1.

[0082] Next, a base layer 2 is formed on one surface of the resin substrate 1.

[0083] Specifically, a base layer 2 can be formed by applying a composition containing, for example, an organosilane or organometallic compound, a polyol compound, and an isocyanate compound onto one surface of a resin substrate 1, and then heating and drying it. At this time, the heating temperature is, for example, 50 to 200°C, and the drying time is, for example, about 10 seconds to 10 minutes.

[0084] Next, an inorganic oxide layer 3 is formed on top of the base layer 2.

[0085] The inorganic oxide layer 3 can be formed, for example, by a vacuum deposition method. Examples of vacuum deposition methods include physical vapor deposition and chemical vapor deposition. Examples of physical vapor deposition methods include vacuum evaporation, sputtering evaporation, and ion plating. Vacuum evaporation is particularly preferred among physical vapor deposition methods. Examples of vacuum evaporation methods include resistance heating vacuum evaporation, EB (Electron Beam) heating vacuum evaporation, and induction heating vacuum evaporation. Examples of chemical vapor deposition methods include thermal CVD, plasma CVD, and photoCVD.

[0086] Next, a gas barrier layer 4 is formed on the inorganic oxide layer 3 (gas barrier layer formation step).

[0087] The gas barrier layer 4 can be formed, for example, by applying a gas barrier layer-forming composition to the surface of the inorganic oxide layer 3 opposite to the underlying layer 2 and drying it.

[0088] Known methods can be used to apply the gas barrier layer-forming composition. Specifically, examples of application methods include wet film formation methods such as roll coating, gravure coating, dip coating, reverse coating, wire bar coating, die coating, screen printing, and spray coating.

[0089] As a method for drying a coating film made of a gas barrier layer forming composition, known drying methods such as hot air drying, hot roll drying, and infrared irradiation can be used. The drying temperature of the coating film can be, for example, 50 to 200°C. The drying time varies depending on the thickness of the coating film, the drying temperature, etc., but can be, for example, 1 second to 5 minutes.

[0090] The manufacturing of the gas barrier film 10 is thus completed.

[0091] <Laminate> Next, an embodiment of the laminate of the present disclosure will be described with reference to Figure 2. In Figure 2, the same reference numerals are used for components that are the same as those in Figure 1, and redundant descriptions are omitted.

[0092] Figure 2 is a schematic cross-sectional view showing one embodiment of the laminate of the present disclosure. As shown in Figure 2, the laminate 20 comprises a gas barrier film 10 and a sealant layer 21 laminated on the gas barrier film 10, the sealant layer 21 being located on one side of the resin substrate 1 of the gas barrier film 10. In Figure 2, the gas barrier layer 4 of the gas barrier film 10 and the sealant layer 21 are bonded together by an adhesive layer 22.

[0093] For example, the adhesive layer 22 can be made from a polyester-isocyanate resin, a urethane resin, or a polyether resin. For use in retort processing, a two-component curing urethane adhesive with retort resistance is preferably used.

[0094] (Sealant layer) Examples of materials for the sealant layer 21 include thermoplastic resins such as polyolefin resins and polyester resins, but polyolefin resins are generally used. Specifically, as polyolefin resins, ethylene-based resins such as low-density polyethylene resin (LDPE), medium-density polyethylene resin (MDPE), linear low-density polyethylene resin (LLDPE), ethylene-vinyl acetate copolymer (EVA), ethylene-α-olefin copolymer, and ethylene-(meth)acrylic acid copolymer, as well as polypropylene-based resins such as homopolypropylene resin (PP), propylene-ethylene random copolymer, propylene-ethylene block copolymer, and propylene-α-olefin copolymer, or mixtures thereof can be used. The material for the sealant layer 21 can be appropriately selected from the above-mentioned thermoplastic resins depending on the intended use and temperature conditions such as boiling or retorting.

[0095] The thickness of the sealant layer 21 is determined appropriately depending on the mass of the contents and the shape of the packaging bag, but it is preferably 30 to 150 μm from the viewpoint of the flexibility and adhesion of the laminate 20.

[0096] From the viewpoint of obtaining a laminate made of a single material (monomaterial) with excellent recyclability, it is preferable that in the laminate 20, the resin substrate 1 and the sealant layer 21 are both made of the same material, more preferably both are polyolefin films, and even more preferably both are polyethylene films or polypropylene films.

[0097] <Method for manufacturing laminates> Next, a method for manufacturing the laminate 20 will be described.

[0098] First, the gas barrier film 10 is manufactured using the gas barrier film manufacturing method described above (gas barrier film manufacturing process).

[0099] Next, the sealant layer 21 is bonded to one side of the resin substrate 1 of the gas barrier film 10 using an adhesive layer 22, and the two layers are laminated to obtain a laminate 20 (sealant layer lamination step).

[0100] Since the manufactured laminate 20 has a sealant layer 21, it becomes possible to easily manufacture a packaging bag in which sealing can be ensured by joining the sealant layers 21 together.

[0101] Although the laminate 20 has an adhesive layer 22, the adhesive layer 22 may be omitted if the sealant layer 21 is made of the thermoplastic resin described above and can be bonded to the gas barrier layer 4 of the gas barrier film 10 by heat fusion. In this case, the sealant layer 21 can be bonded to the resin substrate 1 by an extrusion lamination method, in which the gas barrier film 10 described above is heated and melted, and then extruded and bonded in a curtain-like manner.

[0102] <Packaging bag> Next, embodiments of the packaging bag of the present disclosure will be described. The packaging bag is formed by using a laminate 20 and joining sealant layers 21 together. Since the packaging bag is formed using a laminate 20 having sealant layers 21, sufficient sealing performance can be ensured.

[0103] <Manufacturing method for packaging bags> Next, we will explain the manufacturing method of packaging bags.

[0104] First, the laminate 20 is manufactured using the manufacturing method for the laminate 20 described above (laminated product manufacturing process).

[0105] Next, the laminate 20 is used to join the sealant layers 21 together to form an opening, thereby obtaining a joint. After placing the contents, such as food or pharmaceuticals, through the opening of this joint, the opening of the joint is sealed to manufacture a packaging bag (laminated joint joining process).

[0106] In the above laminate joining process, the joined body can be formed by folding one laminate 20 so that the sealant layers 21 face each other, and then heat-sealing the peripheral edges of the opposing sealant layers 21 together, or by overlapping two laminates 20 so that the sealant layers 21 face each other, and then heat-sealing the peripheral edges of the opposing sealant layers 21 together.

[0107] In addition, the laminate joining process described above does not necessarily require the joined body to contain any contents. In this case, the joined body with an opening becomes a packaging bag.

[0108] This disclosure is not limited to the embodiments described above. For example, in the embodiments described above, the gas barrier film 10 comprises a base layer 2 and an inorganic oxide layer 3, but at least one of the base layer 2 and the inorganic oxide layer 3 can be omitted.

[0109] Furthermore, in the above embodiment, the sealant layer 21 is arranged on one side (the gas barrier layer 4 side) of the resin substrate 1 of the gas barrier film 10 in the laminate 20, but the sealant layer 21 may also be arranged on the other side (the side opposite to the gas barrier layer 4) of the resin substrate 1. [Examples]

[0110] The present disclosure will be described in detail below with reference to examples, but the present disclosure is not limited to these examples.

[0111] <Preparation of aqueous dispersion of aqueous polyurethane resin> (Aqueous dispersion of aqueous polyurethane resin (A0)) An aqueous dispersion of a polyurethane resin (A0) was prepared by dispersing an acid group-containing polyurethane resin that satisfies the following conditions in water. Acid group-containing polyurethane resin (polyurethane resin having structural units derived from polyisocyanate components, polyhydroxy acid components, polyol components, and chain extension agent components; total concentration of urethane groups and urea groups: 40% by mass; percentage of units composed of hydrocarbon rings based on the total amount of constituent units: 50% by mass; acid value: 40 mg KOH / g; number average molecular weight: 900)

[0112] (Aqueous dispersion of aqueous polyurethane resin (A1)) A polyamine compound (dimethylethanolamine, isoholodiamine) was added to an aqueous dispersion of aqueous polyurethane resin (A0) in a molar ratio (acid group / basic nitrogen atom) of 0.1 / 1 relative to the aqueous polyurethane resin, and the mixture was then passed through a filter with a mesh size of 5 μm. The solid content concentration of the dispersion that passed through the filter was adjusted to 30% by mass to obtain an aqueous dispersion of aqueous polyurethane resin (A1).

[0113] (Aqueous dispersion of aqueous polyurethane resin (A2)~(A5)) Aqueous dispersions of aqueous polyurethane resin (A2) to (A5) were obtained in the same manner as the preparation method for aqueous dispersion of aqueous polyurethane resin (A1), except that the mesh opening of the filter used was changed to 8 μm, 10 μm, 20 μm, and 100 μm.

[0114] <Particle size distribution measurement> For aqueous dispersions of aqueous polyurethane resin (A1) to (A5), the particle size distribution of the equivalent circle diameter of polyurethane resin particles contained in the dispersion was measured using the following measuring instruments and conditions. From the results of measuring 300 particles, the average equivalent circle diameter, the maximum equivalent circle diameter, and the number of polyurethane resin particles with an equivalent circle diameter of 10 μm or more out of 300 particles were determined. The results are shown in Table 1. If the maximum equivalent circle diameter is 20 μm or less, it can be concluded that the aqueous dispersion of aqueous polyurethane resin does not contain polyurethane resin particles with an equivalent circle diameter exceeding 20 μm.

[0115] (Measurement equipment and conditions) Equipment used: Particle shape image analyzer (manufactured by Seishin Corporation, product name: PITA-04) Analysis principle: Dynamic image analysis method Particle size measurement range: 1 to 1000 μm Particle size distribution: Volume- and area-equivalent particle size distribution

[0116] [Table 1]

[0117] The materials used in the examples and comparative examples are shown below. (Water-soluble polymer) Polyvinyl alcohol with a saponification degree of 98.5% and a polymerization degree of 500 (product name: PVA-105, manufactured by Kuraray Co., Ltd.). (Silane coupling agent) 3-Glycidoxypropyltriethoxysilane (Trade name: KBE-403, manufactured by Shin-Etsu Silicone Co., Ltd.).

[0118] (Resin base material) Biaxially oriented polypropylene film (manufactured by Mitsui Chemicals Tohcello Co., Ltd., product name: U-1, thickness 20 μm, hereinafter referred to as "OPP"). Biaxially oriented polyethylene terephthalate film (hereinafter referred to as "PET"). High-density polyethylene film (hereinafter referred to as "HDPE").

[0119] (Composition for forming base layer) Acrylic polyol and tolylene diisocyanate were mixed so that the number of NCO groups in tolylene diisocyanate was equal to the number of OH groups in acrylic polyol, and the mixture was diluted with ethyl acetate to a total solid content (total amount of acrylic polyol and tolylene diisocyanate) of 5% by mass. β-(3,4) was added to the diluted mixture. - Epoxycyclohexyl) ethyl A base layer-forming composition (anchor coating agent) was prepared by adding trimethoxysilane in an amount of 5 parts by mass per 100 parts by mass of the total amount of acrylic polyol and tolylene diisocyanate, and then mixing them.

[0120] (Sealant layer) Unstretched polypropylene film (hereinafter referred to as "CPP"). Linear low-density polyethylene resin film (hereinafter referred to as "LLDPE").

[0121] [Example 1] (Preparation of composition for forming a gas barrier layer) A gas barrier layer-forming composition was obtained by blending an aqueous dispersion of aqueous polyurethane resin (A1) in a ratio of 55 parts by mass (solids), a water-soluble polymer in a ratio of 35 parts by mass, and a silane coupling agent in a ratio of 10 parts by mass.

[0122] (Fabrication of laminates) A coating film was formed on an OPP resin substrate by applying a base layer formation composition using a gravure coating method. The resulting coating film was heated at 120°C for 10 seconds and dried to form a 100 nm thick base layer. Next, silicon oxide was evaporated using an electron beam heating vacuum deposition apparatus to form a 40 nm thick inorganic oxide layer on the base layer. Then, a gas barrier layer formation composition was applied to the inorganic oxide layer using a bar coater. The resulting coating film was dried in a 60°C oven for 1 minute to form a 500 nm thick gas barrier layer, obtaining a gas barrier film having a laminated structure of resin substrate / base layer / inorganic oxide layer / gas barrier layer.

[0123] A laminate was obtained by dry laminating a CPP (compressed plastic) sealant layer onto the gas barrier layer of a gas barrier film using an adhesive. Two-component urethane-based adhesives (manufactured by Mitsui Chemicals, Inc., product names: Takelac A525 and Takenate A52) were used as the adhesive.

[0124] From the resulting laminate, a sample measuring 148 mm x 210 mm was cut out. The two cut-out samples were stacked so that their sealant layers faced each other, and the pouch was heat-sealed on three sides to obtain a packaging bag.

[0125] [Examples 2-4 and Comparative Example 1] A gas barrier layer-forming composition, a gas barrier film, a laminate, and a packaging bag were prepared in the same manner as in Example 1, except that aqueous dispersions of aqueous polyurethane resin (A2) to (A5) were used instead of aqueous dispersion of aqueous polyurethane resin (A1).

[0126] [Examples 5-8 and Comparative Example 2] Except for using HDPE as the resin substrate and LLDPE as the sealant layer, gas barrier layer-forming compositions, gas barrier films, laminates, and packaging bags were prepared in the same manner as in Examples 1-4 and Comparative Example 1.

[0127] [Comparative Example 3] Except for using PET instead of HDPE as the resin substrate, a gas barrier layer-forming composition, a gas barrier film, a laminate, and a packaging bag were prepared in the same manner as in Comparative Example 2.

[0128] [Examples 9-12 and Comparative Example 4] In preparing the gas barrier layer-forming composition, a gas barrier film, a laminate, and a packaging bag were prepared in the same manner as in Examples 1 to 4 and Comparative Example 1, except that an aqueous dispersion of aqueous polyurethane resin was blended in a ratio of 59 parts by mass (solids), a water-soluble polymer in a ratio of 31 parts by mass, and a silane coupling agent in a ratio of 10 parts by mass.

[0129] [Examples 13-14 and Comparative Example 5] In preparing the gas barrier layer-forming composition, a gas barrier film, a laminate, and a packaging bag were prepared in the same manner as in Examples 1 to 4 and Comparative Example 1, except that an aqueous dispersion of aqueous polyurethane resin was blended in a ratio of 72 parts by mass (solids), 18 parts by mass of a water-soluble polymer, and 10 parts by mass of a silane coupling agent.

[0130] [Comparative Example 6] Except for using PET instead of OPP as the resin substrate, a gas barrier layer-forming composition, a gas barrier film, a laminate, and a packaging bag were prepared in the same manner as in Comparative Example 5.

[0131] <Evaluation of gas barrier properties> (Preparation of test samples) The laminates obtained in each example were used as test samples before retorting. On the other hand, test samples after retorting were prepared as follows: 250 ml of distilled water was filled into the packaging bags obtained in each example, and a sealed pouch was created by heat-sealing the sealant layer. The resulting pouches were subjected to heat treatment (retorting) at 121°C for 30 minutes. The laminates after this retorting treatment were used as test samples after retorting.

[0132] (Measurement of oxygen permeability (OTR)) Using an oxygen permeability measuring device (product name "OX-TRAN2 / 20", manufactured by MOCON), the oxygen permeability (unit: cc / m³) of the above test sample was measured under conditions of 30°C and 70% relative humidity. 2 The temperature (day·atm) was measured. The measurement was performed in accordance with JIS K-7126-2. The results are shown in Table 2.

[0133] (Measurement of water vapor transmission rate (WTR)) Using a water vapor transmission rate measuring device (product name "PERMATRAN3 / 31", manufactured by MOCON), the above test sample was measured for water vapor transmission rate (unit: g / m³) under conditions of 40°C and 90% relative humidity. 2 The measurement was taken (day). The measurement was performed in accordance with JIS K-7129. The results are shown in Table 2.

[0134] [Table 2] [Explanation of Symbols]

[0135] 1...Resin substrate, 2...Underlayer, 3...Inorganic oxide layer, 4...Gas barrier layer, 10...Gas barrier film, 20...Laminate, 21...Sealant layer, 22...Adhesive layer.

Claims

1. A gas barrier layer forming composition comprising an aqueous polyurethane resin (A) containing an acid group-containing polyurethane resin, a water-soluble polymer (B), and an aqueous medium containing water, The aqueous polyurethane resin (A) does not contain polyurethane resin particles with an equivalent circular diameter exceeding 20 μm. The average equivalent diameter of the polyurethane resin particles in the aqueous polyurethane resin (A) is 5.0 to 10 μm. A gas barrier layer forming composition wherein the mass ratio of the solid content of the aqueous polyurethane resin (A) and the water-soluble polymer (B) (aqueous polyurethane resin (A) / water-soluble polymer (B)) is 85 / 15 to 10 / 90.

2. The gas barrier layer forming composition according to claim 1, further comprising a silane coupling agent (C).

3. A gas barrier film comprising a resin substrate and a gas barrier layer formed on one side of the resin substrate using the gas barrier layer forming composition according to claim 1 or 2.

4. The gas barrier film according to claim 3, wherein the thickness of the gas barrier layer in areas where polyurethane resin particles with an equivalent circular diameter exceeding 10 μm are not present is 0.1 to 10 μm.

5. The gas barrier film according to claim 3 or 4, further comprising an inorganic oxide layer containing an inorganic oxide between the resin substrate and the gas barrier layer.

6. The gas barrier film according to any one of claims 3 to 5, wherein the resin substrate is a polyolefin film.

7. A laminate comprising a gas barrier film according to any one of claims 3 to 6, and a sealant layer laminated on the gas barrier film.

8. The laminate according to claim 7, wherein the resin substrate and the sealant layer in the gas barrier film are both polyethylene films, or both are polypropylene films.

9. A packaging bag formed by joining the sealant layers together using the laminate described in claim 7 or 8.

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