Gas barrier film

Abstract

To provide a gas barrier film or a multilayer gas barrier film that maintains superior gas barrier properties, stretchability, and aesthetics, while achieving reduced production costs and friendliness to the environment.SOLUTION: A gas barrier film includes a polyvinyl alcohol polymer that contains α-olefin units in an amount of 0 to less than 6 mol% and has an average degree of polymerization of about 800-1200.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a gas barrier film or a multi-layer gas barrier film that combines all three elements of oxygen barrier property, stretchability, and aesthetic appearance in a well-balanced manner. [Background technology]

[0002] Packaging films used for packaging foods, medicines, etc., require transparency for the visibility of the contents and for aesthetic reasons, as well as gas barrier properties to prevent oxidation of the contents. Films using conventional polyvinyl alcohol-based polymers (hereinafter sometimes abbreviated as PVA) have good oxygen gas barrier properties when the hygroscopicity is low, but they are highly hygroscopic, and the oxygen gas barrier properties drop rapidly when the relative humidity reaches about 70% or higher. In order to improve the hygroscopicity of this polyvinyl alcohol, ethylene-vinyl alcohol copolymers, which are copolymerized with ethylene, are used (Patent Document 1). However, in the above-mentioned conventional techniques, when ethylene is not copolymerized, it has not been possible to realize a gas barrier film or a multi-layer gas barrier film that has a good balance of all three elements, namely oxygen barrier property, stretchability, and aesthetics. In addition, when ethylene is copolymerized at a high concentration, the cost increases and an organic solvent is required to prepare a coating solution, which causes problems in the working environment. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent Publication No. 2000-318034 Summary of the Invention [Problem to be solved by the invention]

[0004] In view of the limitations of the above-mentioned conventional techniques, an object of the present invention is to provide a gas barrier film or multi-layer gas barrier film that has a good balance of all three elements, namely oxygen barrier property, stretchability, and appearance. Another object of the present invention is to provide a gas barrier film or multi-layer gas barrier film that has excellent gas barrier property, stretchability, and appearance and can be produced at low cost by water painting. [Means for solving the problem]

[0005] As a result of intensive research conducted by the present inventors to solve the above problems, they found that by using a polyvinyl alcohol-based polymer containing 0 to less than 6 mol % of α-olefin units and having an average degree of polymerization of about 800 to 1200, it is possible to improve all of the gas barrier properties, stretchability, and appearance in a well-balanced manner compared to films using polyvinyl alcohol-based polymers of the prior art while suppressing the ethylene content, and thus completed the present invention.

[0006] That is, the present invention and its preferred aspects and embodiments are as follows. [1] A gas barrier film comprising a polyvinyl alcohol polymer containing from 0 to less than 6 mol % of an α-olefin unit and having an average degree of polymerization of about 800 to 1,200. [2] The gas barrier film according to [1], wherein the polyvinyl alcohol-based polymer is a mixture containing at least one polyvinyl alcohol-based polymer (A) containing an α-olefin unit and at least one polyvinyl alcohol-based polymer (B) not containing an α-olefin unit, and the difference between the polymerization degree of the polymer (A) and the polymerization degree of the polymer (B) is 500 or more. [3] The gas barrier film according to [1] or [2], wherein the residual amount of sodium acetate in the polyvinyl alcohol-based polymer is 5000 ppm or less. [4] The gas barrier film according to any one of [1] to [3], wherein the polyvinyl alcohol polymer has an average degree of saponification of 98.50 to 99.50 mol %. [5] The gas barrier film according to any one of [1] to [4], wherein the α-olefin unit is ethylene. [6] The oxygen permeability of the gas barrier film is 250 (ml / m 2 The gas barrier film according to any one of [1] to [5], wherein the gas barrier property is not more than 1.·MPa·day. [7] A multilayer gas barrier film comprising a layer of the gas barrier film according to any one of [1] to [6] and a base film layer. [8] The multilayer gas barrier film according to [7], wherein the base film layer is made of polypropylene. Effect of the Invention

[0007] According to the present invention, it is possible to reduce production costs and to take environmental aspects into consideration while maintaining the excellent gas barrier properties, stretchability and appearance of a gas barrier film or a multilayer gas barrier film. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0008] <Gas barrier film> The present invention is a gas barrier film comprising a polyvinyl alcohol polymer containing 0 to less than 6 mol % of α-olefin units and having an average degree of polymerization of about 800 to 1,200.

[0009] <Polyvinyl alcohol polymer> The polyvinyl alcohol-based polymer constituting the gas barrier film of the present invention contains 0 to less than 6 mol% of α-olefin units and has an average degree of polymerization of about 800 to 1200. When the content of α-olefin units in the polyvinyl alcohol-based polymer is in the range of 0 to less than 6 mol%, the gas barrier film has excellent stretchability, moisture absorption resistance, and oxygen permeability. Furthermore, when the content of α-olefin units is in the above range, it becomes possible to prepare a coating solution using only water without using an organic solvent, thereby improving the working environment. Furthermore, when the average degree of polymerization of the polyvinyl alcohol-based polymer is in the range of about 800 to 1200, film cracks are unlikely to occur when the polyvinyl alcohol copolymer is stretched, and the gas barrier film has excellent stretchability and oxygen permeability. The content of α-olefin units is preferably from 0 to less than 5 mol %, more preferably from 3 to less than 5 mol %, and the average degree of polymerization is preferably from 800 to 1,100, more preferably from 900 to 1,000. The degree of polymerization is measured in accordance with JIS K6726 and is determined from the intrinsic viscosity measured in water at 30±0.1° C. using PVA that has been resaponified and purified.

[0010] The polyvinyl alcohol polymer may be a mixture containing at least one polyvinyl alcohol polymer (A) containing an α-olefin unit and at least one polyvinyl alcohol polymer (B) not containing an α-olefin unit, and the difference between the polymerization degree of the polymer (A) and the polymerization degree of the polymer (B) is preferably at least 500, more preferably at least 700. The at least one polyvinyl alcohol polymer (A) containing an α-olefin unit contains preferably 4 to 10 mol %, more preferably 4 to 8 mol %, and most preferably 4 to 6 mol % of the α-olefin unit. The mass ratio of at least one polymer (A) containing an α-olefin unit to at least one polyvinyl alcohol polymer (B) not containing an α-olefin unit may be adjusted so that the α-olefin unit of the entire mixture of the polyvinyl alcohol polymers (A) and (B) is less than 0 to 6 mol%, and the mass ratio is preferably 30:70 to 70:30, more preferably 40:60 to 60:40, and most preferably 50:50. By blending in this way, the mixture of polyvinyl alcohol polymers becomes more easily dissolved in an aqueous solvent, and as a result, the amount of organic solvent used can be reduced, improving workability and reducing production costs, and making it possible to take environmental aspects into consideration.

[0011] The α-olefin is preferably one having 2 or more carbon atoms, and examples thereof include ethylene, propylene, 1-butene, and isobutene, with ethylene being most preferred in terms of water resistance and moisture absorption resistance.

[0012] The residual amount of sodium acetate in the polyvinyl alcohol-based polymer in the present invention (residual sodium acetate content) is preferably 5000 ppm or less, more preferably 3000 ppm or less, even more preferably 2000 ppm or less, and most preferably 1000 ppm or less, and the average saponification degree of the polyvinyl alcohol-based polymer is preferably in the range of 98.50 to 99.50 mol%, more preferably 98.60 to 99.00 mol%. When the residual amount of sodium acetate in the polyvinyl alcohol copolymer is 5000 ppm or less, the gas barrier film has excellent oxygen permeability under high humidity. When the saponification degree of the polyvinyl alcohol-based polymer is in the range of 98.50 to 99.50 mol%, the film cracks are unlikely to occur when the polyvinyl alcohol-based polymer is stretched, and the gas barrier film has excellent stretchability and excellent oxygen permeability under high humidity. Here, the residual amount of sodium acetate is measured according to JISK6726, and the saponification degree is measured according to JISK6726.

[0013] <Method of manufacturing gas barrier film> The film is produced by preheating a polyvinyl alcohol polymer containing 0 to less than 6 mol % of α-olefin units and having an average degree of polymerization of about 800 to 1200 at a temperature in the range of 165°C to 180°C, and then stretching the polymer in the transverse direction at a temperature in the range of 155 to less than 170°C.

[0014] <Multi-layer gas barrier film> The multilayer gas barrier film of the present invention has a gas barrier film layer and a base film layer.

[0015] <Method of manufacturing multi-layer gas barrier film> The method for producing the multilayer gas barrier film of the present invention involves stretching a laminated film obtained by co-extrusion of a propylene polymer and an adhesive resin in a base film layer in the longitudinal direction, applying a solution of a polyvinyl alcohol-based polymer to the adhesive resin surface, and then stretching the laminated film in the transverse direction. The stretching ratio is usually 3 to 8 times, preferably 4.5 to 6 times, in the longitudinal direction, and 7 to 14 times, preferably 9 to 11 times, in the transverse direction. The stretching temperature depends on the molding temperature of the biaxially stretched film, the thickness of the extruded film, the capacity of the transverse stretching device, etc., but is usually 125°C to 145°C in the longitudinal direction and 155 to less than 165°C in the transverse direction. The longitudinal stretching temperature is not particularly limited as long as it is a temperature at which the propylene polymer and the adhesive resin can be uniformly stretched, but the transverse stretching temperature is 155°C to less than 165°C, depending on the molding speed of the biaxially stretched film, the thickness of the longitudinally stretched sheet, the capacity of the transverse stretching device, etc. If the transverse stretching temperature is 165°C or higher, there is a risk that microcracks will occur frequently in the vinyl alcohol copolymer. In addition, the preheating temperature before stretching can be in the range of 170 to 180° C. before transversely stretching the propylene polymer, although it depends on the forming speed of the biaxially stretched film, the thickness of the longitudinally stretched film, the capacity of the transverse stretching device, etc. In this case, by setting the preheating temperature to less than 175° C., it becomes possible to more effectively suppress the occurrence of microcracks in the vinyl alcohol copolymer, so that the preheating temperature is preferably set to less than 175° C. from the viewpoint of achieving a beautiful appearance.

[0016] The gas barrier film or multi-layer gas barrier film obtained by the manufacturing method of the present invention has an oxygen permeability of 250 ml / m2 or less when measured at 20° C. and 90% RH in accordance with JIS K7126. 2 ·MPa·day or less, preferably 230ml / m 2 ·MPa·day or less, more preferably 200ml / m 2 It exhibits oxygen permeability of less than MPa·day.

[0017] The base film layer constituting the multi-layer gas barrier film of the present invention may be a polyolefin film, a polyester film, a polyamide film, or the like, and is preferably made of polypropylene.

[0018] The thickness of the substrate film (final thickness when stretched) is preferably 15 to 30 μm.

[0019] In order to improve adhesion, an adhesive component layer may be formed between the gas barrier film layer and the base film layer constituting the multilayer gas barrier film of the present invention. As the adhesive component, an adhesive polyolefin is preferably used.

[0020] When the gas barrier film layer is applied onto the base film layer, water alone or a water / alcohol mixed solvent is used as the solvent of the coating liquid. Examples of the alcohol used here include lower aliphatic alcohols such as methanol, ethanol, isopropanol, and n-propanol, and ethanol and isopropanol are particularly preferred. There is no particular restriction on the concentration of the coating liquid, but it is usually determined in the range of 5 to 50% by weight in consideration of the workability during coating. In addition to the composition and water or a water / alcohol mixed solvent as a solvent, surfactants, leveling agents, antifungal agents, preservatives, etc. may be appropriately added to the coating liquid as necessary without any problem.

[0021] The temperature of the coating liquid when it is applied onto the substrate film is usually 20 to 80° C. As a coating method, any of the conventionally known methods such as gravure roll coating method, reverse gravure coating method, reverse roll coating method, Mayer bar coating method, air knife method, doctor knife method, blade method, bar coat method, etc. can be used.

[0022] After forming the gas barrier film layer on the base film layer by the above-mentioned method, there is no problem in further carrying out a heat treatment or a stretching treatment. The heat treatment temperature varies depending on the type of base film layer, and is appropriately selected from the range of 140 to 170°C for polyolefin films and 140 to 240°C for polyester films and polyamide films. EXAMPLES

[0023] The present invention will be described in more detail below with reference to examples, but the present invention is not limited thereto in any way.

[0024] In the following Examples and Comparative Examples, the physical properties and characteristics were evaluated by the following methods. (1) Gas barrier properties (OTR) Measurements were performed using OX-TRAN2 / 20 manufactured by Mocon Co., Ltd., in accordance with JIS K7126 at 20°C and 90% RH. Evaluation was based on the following criteria. 250ml / m 2 Oxygen permeability below MPa·day: Good (〇) 250ml / m 2 Oxygen permeability exceeding ·MPa·day: Poor (×) (2) Appearance (stretchability) A test sample of 100 mm x 100 mm was taken from the stretched gas barrier film, and the number of film cracks and interference patterns (rainbow colors) were visually observed. Evaluation was based on the following criteria. 0 to 3 cracks in the PVA film of 1.5 mm or more in an area of ​​100 mm x 100 mm, and no interference pattern (rainbow color) is visible when the film is reflected in light: Good (〇) 4 or more cracks in the PVA film of 1.5 mm or more in a 100 mm x 100 mm area, or 0 to 3 cracks in the PVA film and an interference pattern (rainbow color) is visible when the film is reflected in light: Poor (×)

[0025] The following materials were used in the examples and comparative examples. (1) Polyvinyl alcohol polymer (A) (A-1) Polyvinyl alcohol polymer (degree of polymerization 400, degree of saponification 98.7 mol%, residual sodium acetate content 100 ppm, ethylene modification rate 7.2 mol%) (A-2) Polyvinyl alcohol polymer (degree of polymerization 1700, degree of saponification 98.4 mol%, residual sodium acetate content 9800 ppm, ethylene modification rate 4.1 mol%) (2) Polyvinyl alcohol polymer (B) (B-1) Polyvinyl alcohol polymer (degree of polymerization 1700, degree of saponification 98.6 mol%, residual sodium acetate content 1600 ppm, ethylene modification rate 0 mol%) (B-2) Polyvinyl alcohol polymer (degree of polymerization 1700, degree of saponification 99.6 mol%, residual sodium acetate content 1800 ppm, ethylene modification rate 0 mol%) (B-3) Polyvinyl alcohol polymer (degree of polymerization 1000, degree of saponification 99.6 mol%, residual sodium acetate content 2400 ppm, ethylene modification rate 0 mol%)

[0026] <Example 1> 40 parts by mass of polyvinyl alcohol polymer (A-1) with a polymerization degree of 400, a saponification degree of 98.7 mol%, a residual sodium acetate of 100 ppm, and an ethylene modification rate of 7.2 mol%, 30 parts by mass of polyvinyl alcohol polymer (B-1) with a polymerization degree of 1700, a saponification degree of 98.6 mol%, a residual sodium acetate of 1600 ppm, and an ethylene modification rate of 0 mol%, and 30 parts by mass of polyvinyl alcohol polymer (B-2) with a polymerization degree of 1700, a saponification degree of 99.6 mol%, a residual sodium acetate of 1800 ppm, and an ethylene modification rate of 0 mol% were mixed, and the mixture was applied to a substrate film layer made of polypropylene and dried. Subsequently, the film continuously applied was introduced into a tenter transverse stretching machine and stretched 10 times in the direction perpendicular to the flow direction of the film (transverse direction) to obtain a multilayer gas barrier film.

[0027] <Example 2> A multilayer gas barrier film was obtained in the same manner as in Example 1, except that polyvinyl alcohol polymer (A-1) and polyvinyl alcohol polymer (B-1) were used and mixed so that the mass ratio of (A-1):(B-1) was 40:60.

[0028] <Example 3> A multilayer gas barrier film was obtained in the same manner as in Example 1, except that polyvinyl alcohol-based polymer (A-1) and polyvinyl alcohol-based polymer (B-1) were used and mixed so that the mass ratio of (A-1):(B-1) was 50:50.

[0029] <Example 4> A multilayer gas barrier film was obtained in the same manner as in Example 1, except that polyvinyl alcohol-based polymer (A-1) and polyvinyl alcohol-based polymer (B-1) were used and mixed so that the mass ratio of (A-1):(B-1) was 60:40.

[0030] <Example 5> A multilayer gas barrier film was obtained in the same manner as in Example 1, except that polyvinyl alcohol-based polymer (A-1) and polyvinyl alcohol-based polymer (B-2) were used and mixed so that the mass ratio of (A-1):(B-2) was 40:60.

[0031] <Example 6> A multilayer gas barrier film was obtained in the same manner as in Example 1, except that polyvinyl alcohol-based polymer (A-1) and polyvinyl alcohol-based polymer (B-2) were used and mixed so that the mass ratio of (A-1):(B-2) was 50:50.

[0032] <Example 7> A multilayer gas barrier film was obtained in the same manner as in Example 1, except that polyvinyl alcohol-based polymer (A-1) and polyvinyl alcohol-based polymer (B-2) were used and mixed so that the mass ratio of (A-1):(B-2) was 60:40.

[0033] <Example 8> A multilayer gas barrier film was obtained in the same manner as in Example 1, except that 15 parts by mass of polyvinyl alcohol-based polymer (B-1) and 85 parts by mass of polyvinyl alcohol-based polymer (B-3) having a polymerization degree of 1000, a saponification degree of 99.6 mol%, a residual sodium acetate content of 2400 ppm, and an ethylene modification rate of 0 mol% were used.

[0034] <Comparative Example 1> A multi-layer gas barrier film was obtained in the same manner as in Example 1, except that 100 parts by mass of the polyvinyl alcohol polymer (A-1) was used.

[0035] <Comparative Example 2> A multi-layer gas barrier film was obtained in the same manner as in Example 1, except that 100 parts by mass of the polyvinyl alcohol polymer (B-2) was used.

[0036] <Comparative Example 3> A gas barrier film was obtained in the same manner as in Example 1, except that 100 parts by mass of a polyvinyl alcohol polymer (A-2) having a degree of polymerization of 1700, a degree of saponification of 98.4 mol%, a residual sodium acetate content of 9800 ppm, and an ethylene modification rate of 4.1 mol% was used.

[0037] The blending ratios of the gas barrier films of Examples 1 to 8 and Comparative Examples 1 to 3 are shown in Table 1, and the results are shown in Table 2. [Table 1]

[0038] [Table 2]

[0039] The multilayer gas barrier film of the present invention had a good balance of all three elements, namely oxygen barrier property, stretchability, and appearance, whereas the multilayer gas barrier film of Comparative Example 1-3 had poor appearance and / or oxygen permeability. [Industrial Applicability]

[0040] The gas barrier film or multilayer gas barrier film of the present invention has a good balance of all three elements, namely oxygen barrier property, stretchability, and aesthetics, and can be used as a packaging film for all kinds of packaged items, including dried foods such as seaweed and rice crackers, and luxury items such as tobacco. In particular, it can be used as a food packaging material for dried foods such as snacks, rice crackers, biscuits, and peanuts, and can be used in a wide range of applications, including not only dried sweets but also steamed buns with a high moisture content, castella cakes, cut rice cakes, dried bonito flakes, and various delicacies.

Claims

1. A gas barrier film comprising a polyvinyl alcohol polymer containing 0 to less than 6 mol % of α-olefin units and having an average degree of polymerization of about 800 to 1,200.

2. 2. The gas barrier film according to claim 1, wherein the polyvinyl alcohol polymer comprises a mixture containing at least one polyvinyl alcohol polymer (A) containing an α-olefin unit and at least one polyvinyl alcohol polymer (B) not containing an α-olefin unit, and the difference between the degree of polymerization of the polymer (A) and the degree of polymerization of the polymer (B) is 500 or more.

3. 3. The gas barrier film according to claim 1, wherein the polyvinyl alcohol polymer has a residual sodium acetate content of 5,000 ppm or less.

4. 3. The gas barrier film according to claim 1, wherein the polyvinyl alcohol polymer has an average degree of saponification of 98.50 to 99.50 mol %.

5. 3. The gas barrier film according to claim 1, wherein the α-olefin unit is ethylene.

6. The oxygen permeability of the gas barrier film is 250 (ml / m ２ 3. The gas barrier film according to claim 1 or 2, wherein the gas barrier strength is 1 / 2 MPa / day or less.

7. A multilayer gas barrier film comprising a layer of the gas barrier film according to claim 1 or 2 and a base film layer.

8. The multilayer gas barrier film according to claim 7 , wherein the base film layer is made of polypropylene.