Gas barrier film and packaging material

Abstract

To provide a gas barrier film including a polylactic acid-based biodegradable film, having adhesion with an inorganic layer, and exhibiting a high gas barrier property at high temperature and high humidity.SOLUTION: There is provided a gas-barrier film including a resin layer and an inorganic layer formed in this order on at least one of surfaces of a base material film, in which the base material film is a polylactic acid-based biodegradable film, and the resin layer contains polyethylenimine and polyvinyl alcohol-based resin.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a gas barrier film and a package using a polylactic acid-based biodegradable film. [Background technology]

[0002] Gas barrier films are widely used to package foodstuffs, pharmaceuticals, medical supplies, industrial parts, etc., to prevent corrosion and decay of the contents and enable long-term storage. In addition, as environmental issues have become a serious social problem, there is a demand for packaging films and gas barrier films with raw material compositions that can reduce the environmental impact.

[0003] In this context, development has been carried out to impart gas barrier properties to biodegradable polylactic acid (PLA) films by forming vapor-deposited films. For example, Patent Document 1 discloses a technique in which an anchor layer made of a styrene-maleic acid based aqueous resin, a cellulose-urethane resin, a polyester resin, a starch based resin, a soluble nitrocellulose-containing resin, or the like is formed to a thickness of 0.1 to 1.0 μm on a polylactic acid based or polyester based biodegradable resin film, which is a vapor deposition biodegradable film material, and a metal vapor deposition layer having a thickness of 100 to 1000 Å is formed thereon. Patent Document 2 discloses a technology for producing a polylactic acid-based biodegradable gas barrier film that has gas barrier properties, transparency, and mechanical properties, and that has a specific degree of planar orientation ΔP and a predetermined value of the difference between the heat of crystalline fusion ΔHm when the film is heated and the heat of crystallization ΔHc generated by crystallization during heating. The technology involves providing a layer of inorganic oxide, inorganic nitride, or inorganic oxynitride on at least one side of the polylactic acid-based biodegradable film by vapor deposition or sputtering. Furthermore, Patent Document 3 discloses a technology (claim 8) in which a coating made of a polysaccharide having uronic acid residues is formed on at least one side of a polylactic acid-based or polyester-based biodegradable resin substrate, and the coating further has a layer of vapor-deposited ceramic. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2003-145677 [Patent Document 2] Japanese Patent Application Laid-Open No. 2006-069218 [Patent Document 3] Japanese Patent Application Laid-Open No. 2008-049606 Summary of the Invention [Problem to be solved by the invention]

[0005] However, in the technology of Patent Document 1, the vapor deposition layer is made as thick as 70 nm, and finally the oxygen permeability is 4 cc / m 2 ·24hrs·atm, water vapor transmission rate 3g / m 2 The gas barrier level was 24 hrs atm (Example 6), which is insufficient as a gas barrier film. Furthermore, the technology of Patent Document 2 has extremely poor adhesion between the polylactic acid-based biodegradable film, which is the base film, and the inorganic layer. Furthermore, the technology of Patent Document 3 aims to impart gas barrier properties to a biodegradable resin substrate by using a coating made of a polysaccharide containing uronic acid residues, which is a natural resource. However, when a vapor deposition layer is formed on the coating, the gas barrier properties of the vapor deposition layer are not exhibited under high temperature and humidity conditions due to moisture absorption by the polysaccharide.

[0006] In view of the above circumstances, an object of the present invention is to provide a gas barrier film that uses a polylactic acid-based biodegradable film, has adhesion to an inorganic layer, and exhibits high gas barrier properties even under high temperature and humidity conditions. [Means for solving the problem]

[0007] The present inventors have conducted extensive research to solve the above problems and have completed the following invention. [1] A gas barrier film comprising a base film having a resin layer and an inorganic layer formed in this order on at least one side thereof, wherein the base film is a polylactic acid-based biodegradable film, and the resin layer contains polyethyleneimine and a polyvinyl alcohol-based resin.

[0008] [2] The gas barrier film according to [1], wherein the resin layer is formed in the order of resin layer (A) and resin layer (B), and when the resin layer (A) is taken as 100% by mass, the resin layer contains 10% by mass or more and 100% by mass or less of polyethyleneimine and 0% by mass or more and 90% by mass or less of a polyvinyl alcohol-based resin, and the resin layer (B) contains a polyvinyl alcohol-based resin.

[0009] [3] The gas barrier film according to [2], wherein the resin layer (A) is composed of 100% by mass of polyethyleneimine.

[0010] [4] When the resin layer (A) is taken as 100% by mass, it contains 10% by mass or more and 50% by mass or less of polyethyleneimine and 50% by mass or more and 90% by mass or less of a polyvinyl alcohol-based resin, The gas barrier film according to [1] or [2], which does not have the resin layer (B).

[0011] [5] The gas barrier film according to any one of [1] to [4], wherein the polyethyleneimine has a number average molecular weight of 30,000 or more and 100,000 or less.

[0012] [6] The gas barrier film according to any one of [1] to [5], which has a resin layer (C) on the inorganic layer.

[0013] [7] The inorganic layer has a thickness of 10 nm or more and 50 nm or less, and a water vapor permeability of 3.5 g / m 2 The gas barrier film according to any one of [1] to [6], wherein the gas barrier film has a viscosity of 1000 saturations per minute or less.

[0014] [8] A package made using the gas barrier film according to any one of [1] to [7]. [Effects of the Invention]

[0015] The gas barrier film of the present invention uses a polylactic acid-based biodegradable film as the base film, which is a raw material composition that can reduce the environmental burden, has adhesion to the inorganic layer, and exhibits high gas barrier properties even under high temperature and humidity conditions.Therefore, when the gas barrier film of the present invention is used in packaging, it can reduce the environmental burden while preventing corrosion and decay of the contents, allowing for long-term storage. [Brief explanation of the drawings]

[0016] [Figure 1] FIG. 1 is a three-dimensional image of the inorganic layer surface of the gas barrier film of Comparative Example 1 after conditioning under conditions of 40° C. and a relative humidity of 90 RH% for 1 hour. [Figure 2] FIG. 2 is a three-dimensional image of the inorganic layer surface of the gas barrier film of Example 1 after conditioning the film under conditions of 40° C. and a relative humidity of 90 RH% for 1 hour. DETAILED DESCRIPTION OF THE INVENTION

[0017] <Gas barrier film> The gas barrier film of the present invention (hereinafter sometimes referred to as the film of the present invention) comprises a base film and a resin layer and an inorganic layer formed in this order on at least one surface of the base film. (Base film) The substrate film used in the gas barrier film of the present invention is a polylactic acid-based biodegradable film containing a polylactic acid resin. Polylactic acid resin is a homopolymer of D-lactic acid or L-lactic acid, or a copolymer thereof. That is, the polylactic acid resin may be any of poly(D-lactic acid) whose structural unit is D-lactic acid, poly(L-lactic acid) whose structural unit is L-lactic acid, and poly(DL-lactic acid) which is a copolymer of L-lactic acid and D-lactic acid, or a mixed resin thereof. It may also be a mixed resin of multiple copolymers of the above-mentioned copolymers with different copolymerization ratios of D-lactic acid and L-lactic acid.

[0018] The copolymer of L-lactic acid and D-lactic acid has a copolymerization ratio of D-lactic acid to L-lactic acid (hereinafter abbreviated as "D / L ratio") of preferably "3 / 97" to "15 / 85" or "85 / 15" to "97 / 3", more preferably "5 / 95" to "15 / 85" or "85 / 15" to "95 / 5", even more preferably "8 / 92" to "15 / 85" or "85 / 15" to "92 / 8", and particularly preferably "10 / 90" to "15 / 85" or "85 / 15" to "90 / 10". It is also possible to blend polylactic acid resins with different D / L ratios, and blending is preferred because it allows for easy adjustment of the D / L ratio of the polylactic acid resin. In this case, the average D / L ratio of the multiple lactic acid polymers should fall within the above range. By blending two or more polylactic acid resins with different D / L ratios and adjusting the crystallinity depending on the intended use, it is possible to achieve a balance between heat resistance and heat shrinkage properties.

[0019] The polylactic acid resin may be copolymerized with a small amount of a copolymerization component, for example, at least one selected from the group consisting of α-hydroxycarboxylic acids other than lactic acid, non-aliphatic dicarboxylic acids such as terephthalic acid, aliphatic dicarboxylic acids such as succinic acid, adipic acid, suberic acid, sebacic acid, and dodecanedioic acid, non-aliphatic diols such as ethylene oxide adducts of bisphenol A, and aliphatic diols such as ethylene glycol, 1,4-butanediol, and 1,4-cyclohexanedimethanol. Examples of the α-hydroxycarboxylic acid unit other than lactic acid include bifunctional aliphatic hydroxycarboxylic acids such as glycolic acid, 3-hydroxybutyric acid, 4-hydroxybutyric acid, 2-hydroxy-n-butyric acid, 2-hydroxy-3,3-dimethylbutyric acid, 2-hydroxy-3-methylbutyric acid, 2-methyllactic acid, and 2-hydroxycaproic acid, and lactones such as caprolactone, butyrolactone, and valerolactone.

[0020] The copolymerization ratio of lactic acid with an α-hydroxycarboxylic acid other than lactic acid, an aliphatic diol, an aliphatic dicarboxylic acid, or the like is not particularly limited. In particular, a higher ratio of lactic acid is preferable because it reduces consumption of petroleum resources, and it is also preferable to copolymerize at a ratio that does not exceed the range of the Vicat softening point described below. Specifically, the copolymer composition ratio (lactic acid / other than lactic acid) of lactic acid with an α-hydroxycarboxylic acid other than lactic acid, an aliphatic diol, or an aliphatic dicarboxylic acid is 95 / 5 to 10 / 90, preferably 90 / 10 to 20 / 80, and more preferably 80 / 20 to 30 / 70. When the copolymerization ratio is within the above range, a film with a good balance of physical properties such as rigidity, transparency, and impact resistance can be obtained. Furthermore, the structure of these copolymers may be a random copolymer, a block copolymer, or a graft copolymer, and any structure is acceptable. However, from the viewpoint of the impact resistance and transparency of the film, a block copolymer or a graft copolymer is preferred.

[0021] The polylactic acid resin may also contain a small amount of a chain extender, such as a diisocyanate compound, an epoxy compound, or an acid anhydride, for the purpose of increasing the molecular weight. The weight-average molecular weight of the polylactic acid resin has a lower limit of 20,000 or more, preferably 40,000 or more, and more preferably 60,000 or more, and an upper limit of 400,000 or less, preferably 350,000 or less, and more preferably 300,000 or less. If the weight-average molecular weight of the polylactic acid resin is 20,000 or more, an appropriate resin cohesive force can be obtained, and insufficient strength and elongation of the film or embrittlement can be suppressed. On the other hand, if the weight-average molecular weight is 400,000 or less, the melt viscosity can be reduced, which is preferable from the viewpoint of film production and improved productivity.

[0022] As a polymerization method for the polylactic acid resin, known methods such as condensation polymerization and ring-opening polymerization can be used. For example, in the condensation polymerization method, D-lactic acid, L-lactic acid, or a mixture thereof can be directly dehydration-condensed polymerized to obtain a polylactic acid resin having a desired composition. In the ring-opening polymerization method, lactide, a cyclic dimer of lactic acid, can be ring-opened and polymerized in the presence of a specific catalyst, optionally with the use of a polymerization regulator, to obtain a polylactic acid resin having a desired composition. The lactide includes DL-lactide, a dimer of L-lactic acid, and these can be mixed and polymerized as needed to obtain a polylactic acid resin having a desired composition and crystallinity.

[0023] The polylactic acid-based biodegradable film containing polylactic acid resin, which is the base film of the present invention, has sufficient film strength, so that the degree of planar orientation of the film ΔP is 3.0 × 10 -3 ~30×10 -3 The degree of planar orientation ΔP is the degree of orientation in the planar direction relative to the thickness direction of the film, and is calculated from the following formula by measuring the refractive indexes in three orthogonal axial directions. ΔP={(γ+β) / 2}-α Here, α is the refractive index in the film thickness direction, and γ and β are the refractive indices of two orthogonal axes parallel to the film surface, with the relationship α<β<γ. ΔP depends on the degree of crystallinity and crystal orientation, but it is largely dependent on the molecular orientation in the film plane. In other words, for non-oriented sheets and films, it is 1.0 × 10 -3 The following ΔP can be increased by increasing molecular orientation in the film plane, particularly in one or two directions, i.e., the film flow direction and / or the direction perpendicular thereto. Methods for increasing ΔP include known film stretching methods and molecular orientation methods utilizing electric or magnetic fields.

[0024] Examples of film stretching methods include a method in which a sheet-like or cylindrical product melt-extruded from a T-die, I-die, round die, or the like is quenched with a cooling cast roll, water, compressed air, or the like to solidify it into a nearly amorphous state, and then uniaxially or biaxially stretched by a roll method, tenter method, tubular method, etc. Examples of stretching conditions include a stretching temperature of 50 to 100°C, a stretching ratio of 1.5 to 5 times, and a stretching speed of 100% / min to 10,000% / min.

[0025] In order to improve the thermal dimensional stability of polylactic acid-based biodegradable films against the thermal load when forming resin layers and inorganic layers, it is preferable that the difference (ΔHm-ΔHc) between the heat of crystalline fusion during heating, ΔHm, and the heat of crystallization, ΔHc, generated by crystallization during heating is 20 J / g or more, and that {(ΔHm-ΔHc) / ΔHm} is 0.75 or more. The above ΔHm and ΔHc are determined by differential scanning calorimetry (DSC), where ΔHm is the amount of heat required to melt all crystals when the temperature is increased at a rate of 10°C / min and is determined from the area of ​​the endothermic peak due to crystal melting, and ΔHc is determined from the area of ​​the exothermic peak generated during crystallization during the temperature increase process.

[0026] ΔHm is primarily dependent on the crystallinity of the polylactic acid resin itself, with the higher the crystallinity, the larger the value. For a complete homopolymer of L-lactic acid or D-lactic acid without copolymers, the value is 60 J / g or higher, while for copolymers of these two types of lactic acid, ΔHm varies depending on the composition ratio. ΔHc is an index related to the crystallinity of the film at that time relative to the crystallinity of the polylactic acid resin. The larger the ΔHc, the more the film crystallizes during the heating process, indicating that the film's crystallinity is relatively low compared to the crystallinity of the polylactic acid resin. Conversely, a small ΔHc indicates that the film's crystallinity is relatively high compared to the crystallinity of the polylactic acid resin. Therefore, one approach to increasing (ΔHm - ΔHc) is to produce a film with a relatively high degree of crystallinity using a highly crystalline polylactic acid resin as the raw material. The crystallinity of the film depends to a large extent on the composition of the polylactic acid resin. To achieve a ΔHm of 20 J / g or more for the polylactic acid resin itself, when producing a copolymer from L-lactic acid and D-lactic acid, it is preferable to adjust the composition ratio (L-lactic acid:D-lactic acid) between 100:0 and 94:6, or between 0:100 and 6:94. Furthermore, to reduce ΔHc and increase the crystallinity of the film, it is effective to select the film forming conditions. For example, to increase the crystallinity of the film during the forming process, especially during biaxial stretching using the tenter method, methods such as increasing the stretch ratio to promote oriented crystallization or heat treatment in an atmosphere above the crystallization temperature after stretching are useful. Furthermore, the larger ΔP, the lower the crystallization temperature tends to be. For example, thermal dimensional stability can be imparted by heat treatment at a temperature in the range of 70°C to 170°C, preferably 90°C or higher, for 3 seconds or more. The higher the heat treatment temperature and the longer the heat treatment time, the more the thermal dimensional stability of the polylactic acid-based biodegradable film tends to improve.

[0027] The thickness of the polylactic acid-based biodegradable film can be appropriately selected depending on the application, but is preferably 5 to 1000 μm, and more preferably 15 to 50 μm, for example.

[0028] (resin layer) The gas barrier film of the present invention comprises a base film and a resin layer and an inorganic layer formed in this order on at least one surface of the base film. In order to achieve gas barrier properties, it is useful to form an inorganic layer using a polyvinyl alcohol-based resin in the resin layer, but if only a polyvinyl alcohol-based resin is used in the resin layer, gas barrier properties cannot be obtained under high-temperature and humid conditions. The inventors have investigated the reasons for this, and found that the polyvinyl alcohol-based resin is hygroscopic, so that the resin layer swells and expands under high-temperature and humid conditions, causing damage to the inorganic film, and that the polyvinyl alcohol-based resin has a weak bonding strength with the surface of a polylactic acid-based biodegradable film, causing interlayer delamination. They then found that in order to prevent the polyvinyl alcohol-based resin in the resin layer from swelling and to improve adhesion to the surface of a polylactic acid-based biodegradable film, it is necessary for the resin layer to contain polyethyleneimine and a polyvinyl alcohol-based resin.

[0029] Specific examples of the resin layer of the gas barrier film of the present invention containing polyethyleneimine and a polyvinyl alcohol-based resin include the following (i) and (ii). (i) The resin layer is formed of two layers, resin layer (A) and resin layer (B) in this order, and when resin layer (A) is taken as 100% by mass, resin layer (A) contains 10% by mass or more and 100% by mass or less of polyethyleneimine and 0% by mass or more and 90% by mass or less of polyvinyl alcohol-based resin, and resin layer (B) contains a polyvinyl alcohol-based resin. (ii) When the resin layer is formed of a single layer of resin layer (A) and the resin layer (A) is taken as 100% by mass, the resin layer contains 10% by mass or more and 50% by mass or less of polyethyleneimine and 50% by mass or more and 90% by mass or less of polyvinyl alcohol-based resin.

[0030] In the above (i), when the resin layer is composed of two layers and the resin layer (A) is 100% by mass and the polyethyleneimine is 100% by mass, the polyethyleneimine is highly cationic, and its polar amino group electrostatically interacts and / or covalently bonds with the carbonyl group contained in the polylactic acid-based biodegradable film, and the hydrophobic ethylene group contained in the polyethyleneimine interacts with the methyl group, etc. of the polylactic acid-based biodegradable film, thereby improving the interlayer adhesion between the polylactic acid-based biodegradable film and the resin layer (A). Furthermore, the amino groups of the polyethyleneimine in the resin layer (A) form hydrogen bonds with the hydroxyl groups contained in the polyvinyl alcohol-based resin in the resin layer (B), thereby improving the interlayer adhesion between the resin layer (A) and the resin layer (B) and also contributing to the suppression of moisture absorption and swelling of the polyvinyl alcohol-based resin in the resin layer (B).

[0031] In addition, in the above (i), when the resin layer (A) contains polyethyleneimine and polyvinyl alcohol, the amino groups contained in the polyethyleneimine form hydrogen bonds with the hydroxyl groups and acetate groups contained in the polyvinyl alcohol of the resin layer (A), thereby increasing the cohesive force within the resin layer (A) and suppressing swelling of the polyvinyl alcohol under high temperature and humidity conditions. Furthermore, the interlayer adhesion with the polylactic acid-based biodegradable film is improved due to electrostatic interactions and / or covalent bonds between the remaining amino groups of the polyethyleneimine and the carbonyl groups of the polylactic acid-based biodegradable film, and / or hydrophobic interactions between the polyethyleneimine and the polylactic acid-based biodegradable film. Furthermore, the remaining amino groups of the polyethyleneimine and the hydroxyl groups of the polyvinyl alcohol resin of the resin layer (B) form hydrogen bonds, which contributes to interlayer adhesion with the resin layer (B) and suppression of moisture absorption and swelling of the resin layer (B).

[0032] In the above (i), when the resin layer (A) contains polyethyleneimine and a polyvinyl alcohol-based resin, the resin layer (A) is 100% by mass, and polyethyleneimine is 10% by mass or more and polyvinyl alcohol-based resin is 90% by mass or less. This allows the polyethyleneimine to undergo a crosslinking reaction with the polyvinyl alcohol-based resin of the resin layer (A) through hydrogen bonding, and the excess polyethyleneimine is involved in interlayer bonding with the polylactic acid-based biodegradable film and the resin layer (B), contributing to the adhesion between the layers. The mass content ratio of polyethyleneimine to polyvinyl alcohol resin (polyethyleneimine:polyvinyl alcohol resin) is (10-100):(0-90), preferably (12-70):(30-88), and more preferably (15-50):(50-85).

[0033] In the above (i), the resin layer (B) contains a polyvinyl alcohol-based resin, which has a high affinity with the inorganic layer due to its hydroxyl groups, and the large number of chemical bonding points makes the inorganic film dense, thereby improving the gas barrier properties. The resin layer (B) may contain other components within the range that does not impair the effects of the present invention, such as polyester resins, acrylic resins, polyethyleneimides, isocyanate compounds, carbodiimide compounds, and oxazoline compounds. When the resin layer (B) is taken as 100% by mass, the content of the polyvinyl alcohol resin is preferably from 70 to 100% by mass, more preferably from 80 to 100% by mass.

[0034] In the above (ii), when the resin layer is composed of a single layer of resin layer (A) and resin layer (A) is 100% by mass, by making polyethyleneimine 10% by mass or more and 50% by mass or less and polyvinyl alcohol-based resin 50% by mass or more and 90% by mass or less, the number of crosslinking points due to hydrogen bonding between polyethyleneimine and polyvinyl alcohol-based resin increases, and swelling of the polyvinyl alcohol-based resin is suppressed. Furthermore, the polyethyleneimine and polyvinyl alcohol resins form ionic bonds and hydrogen bonds, respectively, with the inorganic layer, improving the interlayer adhesion between the resin layer (A) and the inorganic layer. The mass content ratio of polyethyleneimine to polyvinyl alcohol resin (polyethyleneimine:polyvinyl alcohol resin) is preferably (10-50):(50-90), more preferably (12-45):(55-88), and even more preferably (15-40):(60-85).

[0035] Polyethyleneimine The polyethyleneimine used in the resin layer of the gas barrier film of the present invention may be any polymer of ethyleneimine. Due to its molecular structure, polyethyleneimine has a high concentration of amine groups (amine value) within the molecule, making it highly reactive and water-soluble. Therefore, when incorporated into the resin layer of the present invention, it reacts and interacts with the components of each layer, significantly contributing to improving the gas barrier properties of the film of the present invention. The amine value is preferably 15 to 25 mmol / g solid, and more preferably 17 to 23 mmol / g solid. The molecular structure of polyethyleneimine is not particularly limited and may be either linear or branched. However, branched structures are preferred because of their low crystallinity and high water solubility. Branched polyethyleneimine contains primary amines, secondary amines, and tertiary amines, and the branching degree is expressed as the molar ratio of tertiary amines to the total of secondary and tertiary amines. A branching degree of less than 30% results in relatively high reactivity of the secondary amines, while a branching degree of 30% or more results in low crystallinity and excellent cold and hot water solubility. The molar ratio of the amine groups of the polyethyleneimine used in the gas barrier film of the present invention (primary amine:secondary amine:tertiary amine) is not particularly limited, but is preferably in the range of (20-50):(30-55):(15-35), and more preferably in the range of (20-40):(40-55):(20-30). The molar ratio of the amine groups can be analyzed by C-NMR. The molecular weight of polyethyleneimine is not particularly limited, but for example, the number average molecular weight is preferably 5,000 to 200,000, more preferably 30,000 to 100,000, and even more preferably 50,000 to 80,000. A number average molecular weight of 5,000 or more improves the flexibility of the resin layer, while a number average molecular weight of 200,000 or less improves the transparency of the resin layer. The number average molecular weight can be analyzed by GPC.

[0036] Polyvinyl alcohol resin The polyvinyl alcohol resin used in the resin layer of the gas barrier film of the present invention may be one in which the acetate groups of polyvinyl acetate, a polymer of vinyl acetate, have been saponified. The degree of saponification is not particularly limited, but from the standpoints of water solubility, crystallinity, and resin layer (coating) strength, it is preferably, for example, 70 mol% or more and 100 mol% or less, and the lower limit is more preferably 80 mol% or more. The average degree of polymerization of the polyvinyl alcohol resin is preferably 200 to 3000, more preferably 300 to 2000, and even more preferably 400 to 1500. A degree of polymerization of 200 or more provides sufficient strength for the resin layer (coating), and a degree of polymerization of 3000 or less provides good water solubility. Furthermore, the polyvinyl alcohol-based resin may be partially modified, for example, butenediol-modified, silanol-modified, or acetoacetyl-modified. In particular, butenediol-modified resins improve cohesion through hydrogen bonding with the amine groups of polyethyleneimine contained in the resin layer, thereby suppressing moisture absorption and swelling and improving the strength of the resin layer (coating). In silanol-modified resins, they react with the inorganic layer, forming a dense inorganic layer and improving gas barrier properties. Furthermore, polyvinyl alcohol modification promotes crystallization and crosslinking of the polyvinyl alcohol-based resin, which is expected to suppress moisture absorption and swelling and improve the strength of the resin layer (coating).

[0037] Resin layer thickness and formation method The total thickness of the resin layers is preferably 10 to 300 nm in terms of solid content. The thickness of the resin layer (A) is preferably 5 to 200 nm, more preferably 15 to 100 nm. The thickness of the resin layer (B) is preferably 30 to 200 nm, more preferably 50 to 150 nm. When the resin layer (A) is composed of 100% by mass of polyethyleneimine, a thinner thickness is preferable in terms of adhesion to the polylactic acid-based biodegradable film.

[0038] The resin layer can be formed by preparing polyethyleneimine and polyvinyl alcohol resins as aqueous solutions, blending them to a predetermined solid content mass ratio and solid content thickness, applying and drying them. In this case, the surface of the polylactic acid biodegradable film on which the resin layer is to be formed may be subjected to surface treatment such as corona treatment, plasma treatment, ultraviolet irradiation, alkali treatment, etc. For example, corona treatment may be used to increase the wettability index of the polylactic acid biodegradable film surface to 40 or higher. The coating method may be a known method such as gravure coating, gravure reverse coating, kiss reverse gravure coating, spin coating, dip coating, or bar coating. The drying method can be, for example, one or a combination of two or more heat application methods such as hot air drying, radiant heat drying, heat roll drying, high frequency irradiation, infrared irradiation, and UV irradiation.

[0039] (Inorganic layer) The gas barrier film of the present invention can suppress the permeation of gases such as water vapor and oxygen gas by forming an inorganic layer via a resin layer. The composition of the inorganic layer is not particularly limited as long as it has gas barrier properties, and examples thereof include inorganic substances, inorganic oxides, inorganic nitrides, and inorganic oxynitrides, and specific examples thereof include silicon oxide, silicon nitride, silicon oxynitride, silicon oxycarbide, silicon oxycarbonitride, aluminum oxide, aluminum nitride, aluminum oxynitride, aluminum oxycarbide, etc., and mixtures thereof. In addition, the inorganic layer may contain alkali metal ions or alkaline earth metal ions to improve the gas barrier properties. The inorganic layer may be one layer or multiple layers.

[0040] The thickness of the inorganic layer of the gas barrier film of the present invention is preferably 1 to 500 nm, more preferably 5 to 100 nm, and even more preferably 10 to 50 nm. When there are a plurality of inorganic layers, the thickness is the total thickness of the layers. The gas barrier film of the present invention has an inorganic layer formed on a polylactic acid-based biodegradable film with a suitable resin layer interposed therebetween, and therefore can exhibit good gas barrier properties even when the inorganic layer is thin. The layer thickness of the inorganic layer can be observed with a transmission electron microscope by preparing an ultrathin cross-section of the gas barrier film.

[0041] For the formation (film deposition) of the inorganic layer, known methods such as physical vapor deposition (PVD) methods like vacuum heating evaporation method, electron beam method, sputtering method, ion plating method, etc., and chemical vapor deposition (CVD) methods can be used. Plasma assist may be combined with the PVD method or CVD method. When there are multiple inorganic layers, multiple inorganic layer film deposition methods may be used. In terms of gas barrier properties, the PVD method is preferred. For example, it is preferable to form an inorganic layer made of silicon oxide represented by SiOx (1.0 < x ≦ 2.0). When the value of x in SiOx is small, the gas barrier property is enhanced, and when the value of x is large, the colorless transparency is good. From the perspective of the balance between the two, 1.5 ≦ x ≦ 2.0 is preferable. The control of the composition of SiOx can be adjusted by the blending composition of the raw materials used, the type of reaction gas, the degree of vacuum, and the deposition rate. The composition of SiOx can be analyzed by X-ray photoelectron spectroscopy (XPS) or the like.

[0042] When combining plasma assist with the PVD method, during vacuum deposition, the deposited material is ionized by plasma while being deposited, or gas ions are irradiated from a separately provided ion source. Due to plasma assist, oxygen atoms can be efficiently incorporated into the inorganic layer, so the transparency can be improved without reducing the gas barrier property of the inorganic layer. Also, since energy can be imparted to the deposited material by plasma assist, a dense inorganic layer can be formed. In addition, since the excited species in the plasma are highly reactive, oxidation, nitridation, carbonization, etc. of the evaporated material by introducing gases such as oxygen, nitrogen, acetylene, etc. can be easily controlled. Therefore, in the case of inorganic oxides such as SiOx and AlOx, when plasma assist is combined compared to the inorganic layer obtained only by the PVD method, even when the value of x is the same, a denser film structure can be obtained and the gas barrier property can be improved.

[0043] (Resin layer (C)) In the gas barrier film of the present invention, a resin layer (C) can be provided on the surface of the inorganic layer for the purpose of protecting the inorganic layer and improving the gas barrier properties. The resin layer (C) may be made of, for example, but is not particularly limited to, resins such as polyvinyl alcohol resins, ethylene vinyl alcohol resins, polyurethane resins, polyester resins, polyolefin resins, acrylic resins, polyvinylidene chloride resins, and polyvinylpyrrolidone resins, and crosslinking agents such as ethyleneimine, isocyanate compounds, carbodiimide compounds, epoxy compounds, oxazoline compounds, and alkoxysilanes.

[0044] The thickness of the resin layer (C) is not particularly limited, but is preferably 10 to 1000 nm, more preferably 50 to 500 nm, in terms of solid content thickness. The resin layer (C) can be formed by a known coating method such as gravure coating, gravure reverse coating, kiss reverse gravure coating, spin coating, bar coating, or die coating. The drying method can be, for example, one or a combination of two or more heat application methods such as hot air drying, radiant heat drying, heat roll drying, high frequency irradiation, infrared irradiation, and UV irradiation.

[0045] (Interlayer adhesion) Polylactic acid-based biodegradable films have low surface activity, so conventional techniques have been unable to maintain adhesion to inorganic layers. However, the gas barrier film of the present invention can maintain adhesion to inorganic layers by using the specific resin layer described above. For example, the inorganic layer surface of the gas barrier film of the present invention is placed opposite the corona-treated surface of an unstretched polypropylene film, and the films are dry-laminated via a urethane-based adhesive for dry lamination to prepare a laminate film. A 15 mm wide test piece is then prepared and a peel test is performed using a tensile tester at a test speed of 300 mm / min and a peel angle of 180 degrees. The higher the peel strength, the more desirable it is, with a peel strength of 5 g / 15 mm or more being preferred, 10 g / 15 mm or more being more preferred, and 30 g / 15 mm or more being even more preferred.

[0046] (gas barrier properties) As described above, the gas barrier film of the present invention contains polyethyleneimine in the resin layer, thereby maintaining adhesion to the polylactic acid-based biodegradable film and suppressing moisture absorption and expansion of the polyvinyl alcohol-based resin, and therefore has high gas barrier properties even under high temperature and humidity conditions. For example, at 40°C and 90% relative humidity, the water vapor transmission rate (WVTR) is 3.5 g / m 2 / day or less is preferable, and 3.0 g / m 2 / day or less is more preferable, and 2.8g / m 2 / day or less is more preferable, and 2.0 g / m 2 / day or less is particularly preferred. The oxygen transmission rate (OTR) of the gas barrier film of the present invention is 1.2 cc / m at 25°C and a relative humidity of 80%. 2 / day / atm or less is preferable, 1.0cc / m 2 / day / atm or less is more preferable, 0.8cc / m 2 / day / atm or less is even more preferable.

[0047] (surface roughness) In order to improve the gas barrier properties of the gas barrier film of the present invention, it is preferable that the formation of cracks on the surface of the inorganic layer is suppressed. From this point of view, the three-dimensional surface roughness (Sa) after the formation of the inorganic layer is preferably 20 nm or less, more preferably 15 nm or less. Furthermore, as described above, in the gas barrier film of the present invention, the hygroscopic swelling of the polyvinyl alcohol resin constituting the resin layer is suppressed, thereby suppressing the occurrence of cracks in the inorganic layer due to the hygroscopic expansion of the resin layer, and the difference (ΔSa) between the surface roughness of the inorganic layer of a gas barrier film that has been conditioned for 1 hour in an atmosphere of 40°C and 90% relative humidity after inorganic layer formation and the surface roughness after the inorganic layer formation is preferably less than 12 nm, more preferably 10 nm or less, and even more preferably 8 nm or less. A small difference in surface roughness (ΔSa) means that the occurrence of cracks in the inorganic layer due to the hygroscopic expansion of the resin layer is suppressed.

[0048] <Package> The gas barrier film of the present invention can be laminated with other films to produce a package. Examples of such other films include polyolefin films, polyamide films, polyester films, and acrylic films, and these can be laminated by known methods such as dry lamination. The form of the packaging body is not particularly limited, but examples include bags, tubes, lids, and bases. The packaging body can be used to package foods, pharmaceuticals, medical supplies, electronic components, industrial components, and the like, and can suppress the permeation of water vapor, oxygen gas, and the like, thereby preventing corrosion and decay of the contents and enabling long-term storage. [Example]

[0049] The present invention will be described below using examples, but the present invention is not limited to these examples. The gas barrier films of Examples and Comparative Examples were produced using the raw materials shown below. <Ingredients> (Polylactic acid biodegradable film) Poly-L-lactic acid (Lacty 1012, manufactured by Shimadzu Corporation) with a mass average molecular weight of 200,000 was extruded through a T-die using a 60 mmφ single-screw extruder and then quenched with a cast roll to obtain an unstretched sheet. The unstretched sheet was then stretched 2.5 times longitudinally at 70°C, then 2.5 times transversely, and then heat-set at 120°C for 30 seconds to obtain a biaxially stretched polylactic acid biodegradable film with a thickness of 20 μm. The planar orientation degree ΔP of the obtained film was 14.8 × 10 -3 , (ΔHm-ΔHc) was 45 J / g, and {(ΔHm-ΔHc) / ΔHm} was 0.90.

[0050] (resin layer) PEI-1: Polyethyleneimine, number average molecular weight 70,000, amine value 18 mmol / g solid, amine group molar ratio [primary amine 25%, secondary amine 50%, tertiary amine 25%] PVA-1: Polyvinyl alcohol, saponification degree 80mol%, polymerization degree 500 PVA-2: Polyvinyl alcohol, saponification degree 88 mol%, polymerization degree 500 PVA-3: Polyvinyl alcohol, saponification degree 98 mol%, polymerization degree 500 PVA-4: Polyvinyl alcohol, saponification degree 99 mol%, polymerization degree 450

[0051] <Preparation of gas barrier film> (Examples 1 to 8) One side of a biaxially stretched polylactic acid biodegradable film was corona-treated, and the aqueous coating solution for resin layer (A) was applied to the corona-treated surface with a wetting index of 40 or higher using a bar coater, followed by air drying at 80°C for 1 minute to form resin layer (A). Subsequently, the aqueous coating solution for resin layer (B) was applied to the surface of resin layer (A) using a bar coater, followed by air drying at 80°C for 1 minute to form resin layer (B). The aqueous coating solutions for resin layer (A) and resin layer (B) were blended to achieve the solid composition ratios and solid thicknesses of the resin layers shown in Table 1. Next, a vacuum heating vapor deposition apparatus was used to apply a 2×10 vacuum to the resin layer (B) surface of the biaxially stretched polylactic acid biodegradable film. -3 A 30 nm thick inorganic layer of silicon oxide (SiOx) (x=1.5) was formed under the condition of Pa, and a gas barrier film was obtained.

[0052] (Examples 9 to 11, Comparative Examples 1 to 4) A gas barrier film was produced in the same manner as in Example 1, except that the resin layer (B) was not formed and an inorganic layer was formed on the surface of the resin layer (A) of the biaxially stretched polylactic acid biodegradable film. The aqueous coating liquid for the resin layer (A) was blended so as to have the solid content composition ratio and solid content thickness of the resin layer shown in Table 2.

[0053] <Preparation of laminated film> A polyurethane-based adhesive for dry lamination was applied to the corona-treated surface of a 60 μm-thick unstretched polypropylene film to a solid thickness of 3 μm, and dried. The film was then placed facing the inorganic layer surface of the gas barrier film obtained in the Examples and Comparative Examples, and dry-laminated with the machine direction (MD) of both films aligned, followed by aging at 40°C for 72 hours to obtain a laminated film. The dry laminating adhesive used was a two-component curing polyurethane adhesive made by blending Toyo-Morton AD900 and CAT-RT85 in a mass ratio of 10:1.5. The prepared laminated film was used to measure the peel strength as described below.

[0054] <Evaluation> The gas barrier films and laminated films obtained in the examples and comparative examples were evaluated as follows, and the results are summarized in Tables 1, 2 and 3. (Water vapor permeability) Using a water vapor transmission rate measuring device (DELTAPERM manufactured by Technolox), the obtained laminated film was set with the unstretched polypropylene film side facing the detector and the polylactic acid biodegradable film side facing the water vapor exposure side, and the water vapor transmission rate (WVTR, unit: g / m) was measured under conditions of 40°C and 90% relative humidity. 2 / day) was measured.

[0055] (oxygen permeability) The oxygen transmission rate (OTR, unit: cc / m) of the obtained laminated film was measured under the conditions of 25°C and 80% relative humidity using an oxygen transmission rate measuring device (OX-TRAN 2 / 21 model manufactured by MOCON) in accordance with JIS K 7126B method. 2 / day / atm) was measured.

[0056] (peel strength) The obtained laminated film was cut into a strip with a width of 15 mm, and one end was partially peeled off. The gas barrier film and unstretched polypropylene film were attached to the chuck of a tensile tester (STA-1150 manufactured by Orientec) and peeled at a test speed of 300 mm / min and a peel angle of 180 degrees to measure the peel strength (unit: g / 15 mm).

[0057] (surface roughness) The surface roughness of the inorganic layer of the gas barrier film after inorganic layer formation and that of the gas barrier film after humidity conditioning at 40°C and 90% relative humidity for 1 hour were analyzed using a scanning white light interference microscope (VertScan, Hitachi High-Tech Science) with an objective lens magnification of 5x and a measurement area of ​​948.76 μm × 711.61 μm to measure the three-dimensional surface roughness Sa (unit: nm). The difference in three-dimensional surface roughness ΔSa (unit: nm) between after inorganic layer formation and after humidity conditioning was also calculated.

[0058] [Table 1]

[0059] [Table 2]

[0060] [Table 3]

[0061] In Examples 1 to 8, the resin layer (A) was made of 100% by mass of polyethyleneimine (PEI-1), and the resin layer (B) was made of 100% by mass of polyvinyl alcohol (PVA-1, -2, -3, -4), and the water vapor permeability at 40°C and a relative humidity of 90% was 3.0 g / m 2 / day or less, oxygen permeability at 25°C and 80% relative humidity is 1.0cc / m 2 The gas barrier properties were good, with a value of 10 g / 15 mm or less per day / atm. The peel strength was 10 g / 15 mm or more, and in Examples 1 to 4 in which the thickness of the resin layer (A) was 25 nm, the peel strength was 30 g / 15 mm or more.

[0062] In Examples 9 to 11, the resin layer was a single layer of resin layer (A) containing polyethyleneimine (PEI-1) and polyvinyl alcohol (PVA-4), and the water vapor permeability under conditions of 40°C and 90% relative humidity was 2.0 g / m 2 / day or less, oxygen permeability at 25°C and 80% relative humidity is 0.8cc / m 2The gas barrier properties were good, with a peel strength of 30 g / 15 mm or more.

[0063] In Comparative Examples 1 to 3, the resin layer consisted of a single resin layer (A) composed solely of polyvinyl alcohol (PVA-1, -2, -4), and the water vapor permeability and oxygen permeability were both high, resulting in insufficient gas barrier properties and a peel strength of less than 5 g / 15 mm. These results demonstrate that when the resin layer is composed solely of polyvinyl alcohol, the adhesion between the polylactic acid-based biodegradable film and the resin layer is insufficient, and gas barrier properties cannot be obtained. In Comparative Example 4, the resin layer consisted of a single resin layer (A) composed only of polyethyleneimine (PEI-1), and the peel strength was 110 g / 15 mm, indicating high interlayer adhesion. However, since polyethyleneimine has low heat resistance, the resin layer was deformed by the heat load during vacuum heating deposition, preventing the formation of a uniform inorganic layer and resulting in no gas barrier properties.

[0064] Furthermore, in Comparative Examples 1 to 3, in which the resin layer was composed solely of polyvinyl alcohol (PVA-1, -2, -4), the change in surface roughness of the inorganic layer before and after humidity conditioning was large, at 12 nm or more. This was due to the occurrence of cracks in the inorganic layer due to moisture absorption and expansion of the polyvinyl alcohol in the resin layer. As an example, Figure 1 shows a three-dimensional image of the inorganic layer surface of Comparative Example 1 after humidity conditioning. The numerous linear areas are cracks. On the other hand, in Examples 1, 2, and 4, in which the resin layer (A) was made of polyethyleneimine and the resin layer (B) was made of polyvinyl alcohol, and in Examples 9 to 11, in which the resin layer (A) contained polyethyleneimine and polyvinyl alcohol, the change in surface roughness of the inorganic layer before and after humidity conditioning was small, at 8 nm or less, indicating that the inclusion of polyethyleneimine and polyvinyl alcohol in the resin layer suppressed the expansion of polyvinyl alcohol even under high-temperature and humidity conditions. As an example, Figure 2 shows a three-dimensional image of the inorganic layer surface after humidity conditioning in Example 1. No cracks were observed. [Industrial Applicability]

[0065] The gas barrier film of the present invention uses a polylactic acid-based biodegradable film as the base film, which helps reduce the environmental impact. In addition, it has adhesion to the inorganic layer and exhibits high gas barrier properties even under high temperature and humidity conditions. Therefore, when the gas barrier film of the present invention is used in a package, it can prevent corrosion and decay of the contents, enabling long-term storage.

Claims

1. A gas barrier film comprising a base film and a resin layer and an inorganic layer formed in this order on at least one surface of the base film, the base film is a polylactic acid-based biodegradable film, The resin layers are formed in the order of resin layer (A) and resin layer (B), When the resin layer (A) is taken as 100% by mass, the resin layer (A) contains 10% by mass or more and 100% by mass or less of polyethyleneimine and 0% by mass or more and 90% by mass or less of a polyvinyl alcohol-based resin, The resin layer (B) contains 70% by mass or more and 100% by mass or less of a polyvinyl alcohol-based resin. A gas barrier film characterized by:

2. 2. The gas barrier film according to claim 1, wherein the resin layer (A) is composed of 100% by mass of polyethyleneimine.

3. When the resin layer (A) is taken as 100% by mass, the resin layer (A) contains 10% by mass or more and 50% by mass or less of polyethyleneimine and 50% by mass or more and 90% by mass or less of a polyvinyl alcohol-based resin. The gas barrier film according to claim 1 .

4. 4. The gas barrier film according to claim 1, wherein the polyethyleneimine has a number average molecular weight of 30,000 or more and 100,000 or less.

5. 5. The gas barrier film according to claim 1, further comprising a resin layer (C) on the inorganic layer.

6. The inorganic layer has a thickness of 10 nm or more and 50 nm or less, and a water vapor permeability of 3.5 g / m ２ 6. The gas barrier film according to claim 1, wherein the gas barrier film has a viscosity of 1000 psi / day or less.

7. A package comprising the gas barrier film according to any one of claims 1 to 6.

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