Gas barrier film and method for producing gas barrier film

Abstract

To provide a gas barrier film having low environmental impact and a sufficient gas barrier performance as a packaging material, and a method of manufacturing the same.SOLUTION: There is provided a gas barrier film, comprising: a base material 10 containing a molecular material as a main component; a gas barrier layer 30 formed on a first surface of the base material; and a coating layer 40 formed on the gas barrier layer. A power spectral density obtained from atomic force microscopy in a range of 1 μm×1 μm on the first surface of the base material satisfies one or more of: a value obtained as 0.002 nm2 / Hz or less at a wavelength of 1 nm; a value obtained as 0.020 nm2 / Hz or less at a wavelength of 10 nm; and a value obtained as 0.300 nm2 / Hz or less at a wavelength of 100 nm.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a gas barrier film suitable for packaging foods, medicines, precision electronic parts, etc., and a method for producing the gas barrier film. [Background technology]

[0002] Packaging materials used for foods and pharmaceuticals are often required to have gas barrier properties that block oxygen, water vapor, and other gases that can cause deterioration of the contents and permeate the packaging material, in order to prevent deterioration of the contents and maintain their functions and properties. Gas barrier films, which use a metal foil such as aluminum as a gas barrier layer that is less affected by temperature, humidity, and the like, are known as packaging materials with gas barrier properties.

[0003] Another known gas barrier film configuration is one in which a vapor-deposited film of inorganic oxide such as silicon oxide or aluminum oxide is formed on a substrate film made of a polymer material by vacuum deposition, sputtering, or the like (see, for example, Patent Document 1). These gas barrier films are transparent and have the ability to block gases such as oxygen and water vapor. Furthermore, polyethylene terephthalate (PET) is often used as the substrate film. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 60-49934 [Patent Document 2] Japanese Patent Application Laid-Open No. 2008-23898 Summary of the Invention [Problem to be solved by the invention]

[0005] Until now, polyethylene terephthalate (PET) has often been used as the base film for gas barrier films. However, in recent years, there has been an increasing demand for gas barrier films that use base films made of polypropylene (PP) or polyethylene (PE) in order to reduce the burden on the environment. Patent Document 1 also describes that a base film made of PP can be used. However, the inventors' studies have revealed that a gas barrier film that simply has aluminum oxide (AlOx) formed as a barrier layer on a PP base film does not have sufficient gas barrier performance.

[0006] In view of the above problems, an object of the present invention is to provide a gas barrier film that has a small environmental impact and sufficient gas barrier performance for use as a packaging material, and a method for producing the same. [Means for solving the problem]

[0007] The first aspect of the present invention is a gas barrier film comprising a substrate mainly composed of polypropylene, a pre-treatment layer formed by plasma treatment with oxygen gas, a gas barrier layer formed on the pre-treatment layer, and a coating layer formed on the gas barrier layer. This gas barrier film has a power spectral density obtained from the surface of the substrate of 1 nm or less. 0.0003 nm 2 / Hz or less at a wavelength of 10 nm 0.0032 nm 2 / Hz or less, and At a wavelength of 100 nm 0.1059 nm 2 / Hz and above Below The gas barrier film is characterized by satisfying the above requirements.

[0008] In a second aspect of the present invention, a surface of a substrate mainly composed of polypropylene is subjected to a plasma treatment with oxygen gas, and the power spectral density obtained by measuring the surface in an area of ​​1 μm×1 μm with an atomic force microscope is 0.0003 nm 2 / Hz or less at a wavelength of 10 nm 0.0032 nm 2 / Hz or less, and At a wavelength of 100 nm 0.1059 nm 2 / Hz and above Below The gas barrier film manufacturing method includes forming a treated surface to fill the gap, forming a gas barrier layer on the treated surface, and forming a coating layer on the gas barrier layer. [Effects of the Invention]

[0009] According to the present invention, it is possible to provide a gas barrier film that has a small environmental impact and has sufficient gas barrier properties as a packaging material. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a schematic cross-sectional view of a gas barrier film according to one embodiment of the present invention. [Figure 2] 1 is a graph showing power spectral densities in Example 1 and Comparative Example 1. DETAILED DESCRIPTION OF THE INVENTION

[0011] Hereinafter, one embodiment of the present invention will be described with reference to FIG.

[0012] 1 is a schematic cross-sectional view of a gas barrier film 1 according to this embodiment. The gas barrier film 1 includes a substrate 10, a pretreatment layer 20, a vapor deposition layer 30, a coating layer 40, an adhesive layer 50, and a sealant layer 60.

[0013] The substrate 10 used in the present invention has two or more resin layers whose main component is polypropylene. The substrate 10 of this embodiment has two resin layers: a base layer and a surface layer laminated on the base layer.

[0014] The substrate 10 having two or more resin layers can be formed, for example, by co-extrusion. The total thickness of the substrate 10, which is the sum of the base layer and the surface layer, can be, for example, 3 to 200 μm, and preferably 15 to 60 μm.

[0015] The resin used to make each layer of the substrate 10 is primarily polypropylene, due to its ease of availability, water vapor barrier properties, and environmental impact. Polypropylene may be a homopolymer, random copolymer, block copolymer, or terpolymer. A homopolymer is a polypropylene composed solely of propylene. A random copolymer is a polypropylene in which the main monomer, propylene, is randomly copolymerized with a different comonomer to form a homogeneous phase. A block copolymer is a polypropylene in which the main monomer, propylene, and the comonomer are copolymerized in blocks or in a rubber-like form to form a heterogeneous phase. A terpolymer is a polypropylene in which the main monomer, propylene, is copolymerized with two different comonomers. These polyolefin resins may be used alone or in a blend of two or more. The base layer 11 is preferably made of a homopolymer, random copolymer, or block copolymer. The surface layer 12 is preferably made of a random copolymer, block copolymer, or terpolymer.

[0016] Each layer formed on the substrate 10 may be formed on both sides of the substrate 10. One or both sides of the substrate 10 may contain various well-known additives and stabilizers, such as antistatic agents, ultraviolet inhibitors, antioxidants, plasticizers, lubricants, etc.

[0017] The power spectrum of the substrate surface can be obtained by an atomic force microscope (AFM), and the cross-sectional profile of the surface roughness obtained from the AFM is processed by Fourier transform and frequency analysis is performed to calculate the power spectrum at each wavelength. The inventors have found that the power spectrum density of the substrate 10 surface is 0.001 nm at a wavelength of 1 nm. 2 / Hz or less, 0.020 nm at a wavelength of 10 nm 2 / Hz or less, 0.200 nm at a wavelength of 100 nm 2 It has been found that when the viscosity is 1 / Hz or less, good gas barrier properties can be obtained.

[0018] The gas barrier film 1 of this embodiment has a gas barrier layer (deposited layer 30) that exhibits good gas barrier properties.

[0019] Before forming the vapor deposition layer 30, a pretreatment layer 20 is formed on the substrate 10. The pretreatment layer 20 is a coating layer of a thermoplastic resin, a thermosetting resin, an ultraviolet curable resin, or the like, or a plasma treatment layer. From the viewpoint of productivity, plasma treatment, which can be performed in-line, is preferable. The plasma treatment method is not particularly limited to glow discharge, and a magnet may be used to increase the plasma density. The gas used during the plasma treatment can be selected from one or more of oxygen, nitrogen, and argon.

[0020] The vapor-deposited layer 30 is mainly composed of aluminum oxide and exhibits barrier properties against predetermined gases such as oxygen, water vapor, etc. The vapor-deposited layer 30 may be either transparent or opaque.

[0021] The thickness of the vapor-deposited layer 30 varies depending on the type, composition, and film-forming method of the inorganic compound used, but can generally be set appropriately within the range of 3 to 300 nm. If the thickness of the vapor-deposited layer 30 is less than 3 nm, a uniform film may not be obtained or the film thickness may be insufficient, which may result in insufficient performance as a gas barrier layer. If the thickness of the vapor-deposited layer 30 exceeds 300 nm, the vapor-deposited layer 30 becomes hard, and external factors such as bending or pulling after film formation may cause the vapor-deposited layer 30 to crack, resulting in a loss of barrier properties. Therefore, the thickness of the vapor-deposited layer 30 is preferably within the range of 6 to 150 nm.

[0022] There is no limitation on the method for forming the deposition layer 30, and for example, vacuum deposition, sputtering, ion plating, plasma vapor deposition (CVD), etc. can be used.

[0023] The coating layer 40 further enhances the barrier properties of the vapor-deposited layer 30. The coating layer 40 is formed using a coating agent whose main component is an aqueous solution or a water / alcohol mixed solution containing a water-soluble polymer and one or more metal alkoxides or their hydrolysates. For example, the coating agent is prepared by mixing a water-soluble polymer dissolved in an aqueous solvent (water or a water / alcohol mixed) with a metal alkoxide, either directly or after being hydrolyzed in advance. The coating layer 40 can be formed by applying this coating agent to the vapor-deposited layer 30 and then drying it.

[0024] The components contained in the coating agent for forming the covering layer 40 will be described in more detail. Examples of water-soluble polymers used in the coating agent include polyvinyl alcohol (PVA), polyvinylpyrrolidone, starch, methyl cellulose, carboxymethyl cellulose, and sodium alginate. PVA is particularly preferred because it provides excellent gas barrier properties. PVA is generally obtained by saponifying polyvinyl acetate. As PVA, either so-called partially saponified PVA, in which several tens of percent of acetate groups remain, or complete PVA, in which only a few percent of acetate groups remain, can be used. PVA that is intermediate between the two may also be used.

[0025] Metal alkoxides used in coating agents are compounds represented by the general formula M(OR)n (M: metals such as Si and Al, R: alkyl groups such as CH3 and C2H5). Specific examples include tetraethoxysilane [Si(OC2H5)4] and triisopropoxyaluminum Al[OCH(CH3)2]3. Examples of silane coupling agents include those with epoxy groups such as 3-glycidoxypropyltrimethoxysilane, those with amino groups such as 3-aminopropyltrimethoxysilane, those with mercapto groups such as 3-mercaptopropyltrimethoxysilane, those with isocyanate groups such as 3-isocyanatopropyltriethoxysilane, and tris-(3-trimethoxysilylpropyl)isocyanurate.

[0026] There is no limitation on the method for applying the coating agent, and any conventionally known method such as commonly used dipping, roll coating, screen printing, spraying, or gravure printing can be appropriately selected.

[0027] Another preferred example of the coating layer 40 is a film containing a polyvalent metal salt of carboxylic acid, which is a reaction product between a carboxy group of a polycarboxylic acid polymer (A) and a polyvalent metal compound (B) (a polyvalent metal salt of polycarboxylic acid film). In this case, the film may be a polyvalent metal salt of polycarboxylic acid film formed by applying a coating agent containing a mixture of a polycarboxylic acid polymer (A) and a polyvalent metal compound (B) and drying the mixture under heating, or a polyvalent metal salt of polycarboxylic acid film formed by applying a coating agent containing a polycarboxylic acid polymer (A) as the main component and drying it to form an A film, applying a coating agent containing a polyvalent metal compound (B) as the main component thereon, and drying the coating agent to form a B film, and then causing a crosslinking reaction between the A and B layers.

[0028] [Polycarboxylic acid polymer (A)] A polycarboxylic acid polymer is a polymer having two or more carboxyl groups in the molecule. Examples of polycarboxylic acid polymers include (co)polymers of ethylenically unsaturated carboxylic acids, copolymers of ethylenically unsaturated carboxylic acids with other ethylenically unsaturated monomers, and acidic polysaccharides having carboxyl groups in the molecule, such as alginic acid, carboxymethylcellulose, and pectin.

[0029] Among the above, from the viewpoint of the gas barrier properties of the resulting gas barrier film, polymers containing a structural unit derived from at least one polymerizable monomer selected from the group consisting of acrylic acid, maleic acid, methacrylic acid, itaconic acid, fumaric acid, and crotonic acid are preferred, and polymers containing a structural unit derived from at least one polymerizable monomer selected from the group consisting of acrylic acid, maleic acid, methacrylic acid, and itaconic acid are particularly preferred.

[0030] When a coating agent containing a polycarboxylic acid polymer (A) as a main component is applied and dried to form a coating A, and then the coating B is formed, some of the carboxy groups of the polycarboxylic acid polymer may be neutralized in advance with a basic compound. By neutralizing some of the carboxy groups of the polycarboxylic acid polymer in advance, the water resistance and heat resistance of the coating A can be further improved.

[0031] The basic compound is preferably at least one basic compound selected from the group consisting of polyvalent metal compounds, monovalent metal compounds, and ammonia. As the polyvalent metal compound, compounds exemplified in the description of the polyvalent metal compound (B) described below can be used. As the monovalent metal compound, for example, sodium hydroxide, potassium hydroxide, etc. can be mentioned.

[0032] [Polyvalent metal compounds (B)] The polyvalent metal compound is not particularly limited as long as it is a compound that reacts with the carboxyl group of the polycarboxylic acid polymer to form a polyvalent metal salt of polycarboxylic acid, and examples thereof include zinc oxide particles, magnesium oxide particles, magnesium methoxide, copper oxide, calcium carbonate, etc. These may be used alone or in combination. From the viewpoint of oxygen barrier properties, zinc oxide is preferred.

[0033] Examples of solvents used in coating agents containing polyvalent metal compound (B) as a main component include water, methyl alcohol, ethyl alcohol, isopropyl alcohol, n-propyl alcohol, n-butyl alcohol, n-pentyl alcohol, dimethyl sulfoxide, dimethylformamide, dimethylacetamide, toluene, hexane, heptane, cyclohexane, acetone, methyl ethyl ketone, diethyl ether, dioxane, tetrahydrofuran, ethyl acetate, and butyl acetate. These solvents may be used alone or in combination of two or more.

[0034] Among these, methyl alcohol, ethyl alcohol, isopropyl alcohol, toluene, ethyl acetate, methyl ethyl ketone, and water are preferred from the viewpoint of coatability, and methyl alcohol, ethyl alcohol, isopropyl alcohol, and water are preferred from the viewpoint of manufacturability.

[0035] When a coating agent containing a polycarboxylic acid polymer (A) and a polyvalent metal compound (B) is applied and dried to form a polycarboxylic acid polyvalent metal salt film, the polycarboxylic acid polyvalent metal salt film can be formed by mixing the polycarboxylic acid polymer (A), the polyvalent metal compound (B), a resin or dispersant soluble or dispersible in water or an alcohol as a solvent, and additives as needed, and applying and drying the resulting coating agent by a known coating method. Examples of coating methods include casting, dipping, roll coating, gravure coating, screen printing, reverse coating, spray coating, kit coating, die coating, metaling bar coating, chamber doctor combined coating, and curtain coating.

[0036] The thickness of the coating layer 40 can be appropriately determined based on the composition of the coating agent, the application conditions, etc., and is not particularly limited. However, if the thickness of the coating layer 40 after drying is 0.01 μm or less, the coating film may not be uniform and sufficient gas barrier properties may not be obtained. If the thickness after drying exceeds 50 μm, cracks may easily occur in the coating layer 40. Therefore, the preferred thickness of the coating layer 40 is, for example, in the range of 0.01 to 50 μm. The optimal thickness of the coating layer 40 is, for example, in the range of 0.1 to 10 μm.

[0037] The sealant layer 60 is a layer that is bonded by heat sealing when forming a bag-shaped package or the like using the gas barrier film 1. Examples of materials for the sealant layer 60 include resin materials such as polyethylene, polypropylene, ethylene-vinyl acetate copolymer, ethylene-methacrylic acid copolymer, ethylene-methacrylic acid ester copolymer, ethylene-acrylic acid copolymer, ethylene-acrylic acid ester copolymer, and metal cross-linked products thereof. The thickness of the sealant layer 60 is determined depending on the purpose, but is, for example, in the range of 15 to 200 μm.

[0038] The adhesive layer 50 bonds the sealant layer 60 and the coating layer 40. By using the adhesive layer 50, the resin film that will become the sealant layer 60 and the substrate 10 on which the vapor deposition layer 30 and the coating layer 40 have been formed can be bonded together by dry lamination. An example of a material for the adhesive layer 50 is a two-component curing polyurethane adhesive. A packaging material can be created by laminating a printing layer and a sealant layer 60 on the coating layer 40. Another film may be interposed between the coating layer 40 and the sealant layer 60. [Example]

[0039] The gas barrier film of this embodiment will be further described using examples and comparative examples, but the present invention is not limited to the specific contents of the examples and comparative examples.

[0040] Example 1 The substrate 10 was a biaxially oriented polypropylene film with a thickness of 20 μm, and the pre-treatment layer 20 was a plasma-treated layer with O2 gas at 100 W·sec / m 2 The treatment strength was calculated as follows: Power density [W / m 2 ] = Input power [W] / Cathode area [m 2 ] Processing time [sec] = Electrode MD width [m] / Processing speed [m / sec] Treatment intensity = Power density [W / m 2 ] Processing time [sec]

[0041] After the plasma treatment was carried out under the above conditions, a deposition layer 30 made of aluminum oxide and having a thickness of 10 nm was formed continuously in a vacuum chamber by electron beam deposition.

[0042] On the deposition layer 30, 10.4 g of tetraethoxysilane was added to 89.6 g of hydrochloric acid (0.1 N), and the mixture was stirred for 30 minutes to hydrolyze the resulting hydrolyzed solution with a solid content of 3 wt% (SiO2 equivalent). The solution was then applied by gravure coating and dried to form a coating layer 40 with a thickness of 0.4 μm.

[0043] Finally, an unstretched polypropylene film (thickness: 30 μm) was attached onto the covering layer 40 by dry lamination using a two-component curing polyurethane adhesive, thereby obtaining a gas barrier film of Example 1.

[0044] Example 2 (However, Example 2 is a reference example.) As the pre-treatment layer 20, a plasma treatment layer using O2 gas was performed at 750 W·sec / m 2 A gas barrier film of Example 2 was produced in the same manner as in Example 1, except that it was formed with a treatment strength of 1000 ppm.

[0045] Example 3 (However, Example 3 is a reference example.) As the pre-treatment layer 20, a plasma treatment layer using Ar gas was performed at 100 W·sec / m 2 A gas barrier film of Example 3 was produced in the same manner as in Example 1, except that it was formed with a treatment strength of 1000 ppm.

[0046] Example 4 (However, Example 4 is a reference example.) As the pre-treatment layer 20, a plasma treatment layer using Ar gas was performed at 750 W·sec / m 2 A gas barrier film of Example 4 was produced in the same manner as in Example 1, except that it was formed with a treatment strength of 1000 ppm.

[0047] (Comparative Example 1) A gas barrier film of Comparative Example 1 was produced in the same manner as in Example 1, except that the pretreatment layer 20 was not formed.

[0048] The evaluation items and measurement methods in each of the examples and comparative examples are shown below.

[0049] (Power spectrum analysis of substrate surface) For power spectrum analysis of the substrate surface, an atomic force microscope (AFM5400L) manufactured by Hitachi High-Tech Science Corporation was used to obtain cross-sectional profile data (units: nm) within a 1 μm x 1 μm range. The obtained cross-sectional waveform was divided into each frequency component using a Fourier transform, and the power spectrum intensity at the frequencies included in each range was integrated for each unit frequency width. The obtained power spectrum intensity was then divided by the number of data points to calculate the power spectrum density, which is the power spectrum per unit frequency. The formula for calculating the power spectrum density is shown below.

[0050] The waveform of the cross-sectional profile is an irregular fluctuation and a superposition of waves of various frequencies, so it can be expressed by the following Fourier integral (1): Fourier component X(f) is a wave e of frequency f i2πft The amplitude (unit: nm) of the

number

[0051] The obtained Fourier components represent the magnitude and phase of the complex components of each frequency component, and are converted into energy (power) for comparison in order to express them as power values ​​per unit frequency width (1 Hz width) so as not to depend on the frequency resolution Δf of the Fourier transform. The frequency resolution Δf is expressed by the following equation (2): Δf=1 / T=f S / N···(2)

[0052] To increase the frequency resolution (reduce Δf), the sampling frequency f S Either lower or increase the number of sampling points N.

[0053] The complex number Z obtained from the Fourier transform is expressed by the following equation (3), where the real component is a, the imaginary component is bi, and the real number is A. Z=a+bi=Ae iθ ···(3)

[0054] Therefore, the power spectrum can be expressed as the absolute value of the complex number |Z|. Power spectrum A=|Z|=√(a 2 +b 2 ) (4)

[0055] Then, in order to convert this power spectrum into a value per unit frequency, the power spectrum was divided by the number of data to obtain the power spectrum density, which is the power spectrum per unit frequency.

[0056] (Evaluation of adhesion of vapor-deposited layer immediately after manufacturing) Test pieces were cut out of the gas barrier film of each example in accordance with JIS Z1707, and the peel strength of the vapor-deposited layer 30 was measured as an index of adhesion using an Orientec Corporation Tensilon universal testing machine RTC-1250. Measurements were performed using two types of peel tests, T-peel and 180° peel, both in the normal state (Dry) and with the measurement site wet (Wet).

[0057] (Gas barrier layer adhesion evaluation after hot water treatment) Two gas barrier films of each example were stacked with the sealant layers 60 facing each other, and three sides were joined by heat sealing to produce a pouch (packaging container) of each example. After filling the pouch of each example with water as the content, the open side was sealed by heat sealing. Then, a boiling treatment (90°C for 30 minutes) was performed as a hot water treatment.

[0058] After the hot water treatment, test pieces were cut out from the part of each pouch that had been in contact with the contents in accordance with JIS Z1707, and the peel strength of the vapor-deposited layer 30 was measured as an index of adhesion using an Orientec Tensilon universal testing machine RTC-1250. Measurements were performed using two types of peel tests, T-peel and 180° peel, both in the normal state (Dry) and with the measurement site wet (Wet).

[0059] (Gas barrier performance evaluation immediately after production and after hot water treatment) The pouches of each example prepared by the above procedure were opened immediately after production and after hot water treatment, and the oxygen transmission rate (OTR) of the gas barrier film (unit: cc / m 2 ·day·atm, measurement conditions: 30℃-70%RH), and water vapor transmission rate (WVTR) (unit: g / m 2 The test was performed under the following conditions: 40°C-90%RH.

[0060] The results are shown in Table 1.

[0061] [Table 1]

[0062] The gas barrier films according to Examples 1 to 4 have a power spectral density of 0.002 nm at a wavelength of 1 nm obtained from the substrate surface. 2 / Hz or less, 0.020 nm at a wavelength of 10 nm 2 / Hz or less, 0.300 nm at a wavelength of 100 nm 2 / Hz or less, a dense barrier layer was formed, and the water vapor barrier property after the coating layer was formed was excellent.

[0063] The gas barrier film according to Comparative Example 1 has a power spectral density of 0.002 nm at a wavelength of 1 nm obtained from the surface of the substrate. 2 / Hz or more, 0.020 nm at a wavelength of 10 nm 2 / Hz or more, 0.300 nm at a wavelength of 100 nm 2 / Hz or more, the water vapor barrier property after the coating layer was formed was inferior to that of Example 1-4.

[0064] A comparison of the power spectral densities in Example 1 and Comparative Example 1 is shown in FIG. [Industrial Applicability]

[0065] The present invention can be used for gas barrier films used for packaging and the like. [Explanation of symbols]

[0066] 1. Gas barrier film 10 Base material 20 Pretreatment layer 30 Deposited layer 40 Covering layer 50 adhesive layer 60 Sealant Layer

Claims

1. A substrate mainly made of polypropylene, a pretreatment layer formed on a first surface of the substrate by plasma treatment with oxygen gas, a gas barrier layer formed on the pretreatment layer, and a coating layer formed on the gas barrier layer, wherein the power spectral density obtained by atomic force microscope measurement within an area of ​​1 μm × 1 μm on the first surface of the substrate is 0.0003 nm at a wavelength of 1 nm. ２ / Hz or less, 0.0032 nm 2 / Hz or less at a wavelength of 10 nm, and 0.1059 nm at a wavelength of 100 nm ２ A gas barrier film characterized by satisfying a viscosity of 1 / Hz or less.

2. 2. The gas barrier film according to claim 1, wherein the gas barrier layer contains one of aluminum, aluminum oxide, silicon oxide, and silicon oxide containing carbon as a main component, and has an average film thickness of 3 nm to 300 nm.

3. 3. The gas barrier film according to claim 1, wherein the coating layer contains one or more alkoxides or hydrolysates thereof, and any one of a water-soluble polymer, a polyvalent metal compound, and a polyvalent metal salt of a carboxylic acid.

4. The water vapor permeability after the coating layer is formed is 0.7 g / m ２ ・day or less, and oxygen permeability is 0.9cc / m ２ 4. The gas barrier film according to claim 1, wherein the gas barrier film has a viscosity of 1000 psi or less.

5. 5. The gas barrier film according to claim 1, further comprising a heat-sealable sealant layer, the sealant layer being bonded to the covering layer by an adhesive layer.

6. 6. The gas barrier film according to claim 1, wherein the peel strength between the substrate and the gas barrier layer or the sealant layer is 1.0 N / 15 mm or more.

7. After hot water treatment at 95°C for 30 minutes, Oxygen permeability is 5.0 cc / m ２ ・day・atm or less, and water vapor permeability is 2.0 g / m ２ ・day or less, 7. The gas barrier film according to claim 1, wherein the peel strength between the substrate and the gas barrier layer or the sealant layer is 1.0 N / 15 mm or more.

8. The surface of a substrate whose main component is polypropylene is subjected to a plasma treatment with oxygen gas, and the power spectral density obtained from atomic force microscope measurement of the surface in an area of ​​1 μm × 1 μm is 0.0003 nm at a wavelength of 1 nm. ２ / Hz or less, 0.0032 nm at a wavelength of 10 nm ２ / Hz or less, and 0.1059 nm at a wavelength of 100 nm ２ Create a processing surface that satisfies / Hz or less, forming a gas barrier layer on the treated surface; A method for producing a gas barrier film, comprising forming a coating layer on the gas barrier layer.

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