JP2001088250A - Gas-barrier film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a film which has high gas-barrier properties even in an atmosphere high in temperature and humidity. SOLUTION: A gas-barrier film in which a layer comprising 10-80 wt.% of an acrylic copolymer containing at least 70 wt.% of an acrylonitrile unit and a mixture comprising 15-80 wt.% of polyvinyl alcohol and 5-50 wt.% of an olefin-maleic anhydride copolymer is formed at least on one side of a thermoplastic resin film is provided.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a gas barrier film suitable for food packaging and the like.

[0002]

2. Description of the Related Art Thermoplastic resin films such as polyamides and polyesters are widely used as packaging materials because of their excellent strength, transparency and moldability. However, when used for applications requiring long-term storage properties, such as retort-treated foods, higher gas barrier properties are required.

In order to improve gas barrier properties, polyvinylidene chloride (P) is coated on the surface of these thermoplastic resin films.
VDC) has been widely used for food packaging and the like, but PVDC generates organic substances such as acidic gas at the time of incineration. Therefore, in recent years, interest in the environment has increased, and a shift to other materials has been strongly desired. ing.

As a material that replaces PVDC, acrylonitrile-based resins exhibit excellent gas barrier properties based on the intermolecular force specific to nitrile groups, and have chemical resistance to acids, alkalis, organic solvents, and the like, as well as flexural modulus, strength, and strength. It is a thermoplastic resin having excellent mechanical properties such as creep properties. In recent years, its value as a material for films, sheets, and containers has been recognized in the fields of foods, agricultural drugs, cosmetics, and the like. Regarding a method of polymerizing an acrylic copolymer latex containing a high fraction of acrylonitrile, a method of introducing an acidic group such as a sulfonic acid group, a sulfuric acid group, a carboxyl group or a salt thereof into the polymer (particularly). Kosho 54
-41638, Japanese Patent Publication No. 55-2207),
A method of carrying out polymerization in the presence of a diene rubber (JP-A-57-1
The high acrylonitrile-containing latex thus obtained has a higher glass transition temperature as the acrylonitrile content increases, and a uniform coating film is formed when the latex is coated on a film. There is a problem that it is difficult to do.

[0005] On the other hand, polyvinyl alcohol (PVA) does not generate toxic gas and has a high gas barrier property in a low humidity atmosphere. However, as the humidity increases, the gas barrier property rapidly decreases, and packaging of foods and the like containing moisture is performed. Can not be used in many cases. A film made of a copolymer of PVA and ethylene (EVOH) is known as a film in which the deterioration of the gas barrier property of PVA under high humidity is improved, but the gas barrier property under high humidity is maintained at a practical level. Therefore, it is necessary to increase the ethylene content to some extent. When EVOH is used as a coating material, it is necessary to dissolve it using an organic solvent or a mixed solvent of water and an organic solvent, which is not desirable from the viewpoint of environmental problems, and requires a step of recovering the organic solvent. Therefore, there is a problem that the cost increases.

[0006] Also, various techniques for waterproofing by cross-linking the molecular chain of PVA using a cross-linking agent have been known in the art.
It is widely known that it is made water-resistant by reacting with a hydroxyl group such as VA or polysaccharide. For example, Japanese Patent Application Laid-Open No. 8-66991 discloses that isobutylene-maleic acid copolymers of 25 to
It has been shown that a layer consisting of 50% partially neutralized material and PVA has excellent water resistance. Also, JP-A-49-164
No. 9 describes a method of making a PVA film water resistant by mixing an alkyl vinyl ether-maleic acid copolymer with PVA. However, water resistance (that is, water insolubility) and gas barrier properties are different properties. Generally, water-soluble polymers are made water-resistant by cross-linking molecules.However, gas barrier properties are properties that prevent the penetration or diffusion of relatively small molecules such as oxygen. For example, a three-dimensional crosslinkable polymer such as an epoxy resin or a phenol resin does not have gas barrier properties. As a method for coating a film with a liquid composition comprising a water-soluble polymer and exhibiting a high gas barrier property even under high humidity, P
A method has been proposed in which an aqueous solution comprising VA or polysaccharide and a partially neutralized product of polyacrylic acid or polymethacrylic acid is coated on a film and heat-treated to crosslink both polymers through ester bonds (Japanese Patent Application Laid-Open No. HEI 9-258572). 10
In order to advance the crosslinking reaction, it is necessary to heat at a high temperature for a long time, and there is a problem in productivity.

[0007]

DISCLOSURE OF THE INVENTION The present inventors have solved the above-mentioned problems and have attempted to provide a film which has a high gas barrier property even under high humidity and can be industrially manufactured at low cost. It is.

[0008]

Means for Solving the Problems As a result of diligent studies, the present inventors have found that an acrylic copolymer containing a high fraction of acrylonitrile units and a specific ratio of PVA and an olefin-maleic anhydride copolymer. The present inventors have found that a film having high gas barrier properties even under high humidity can be industrially produced by applying the liquid to at least one surface of the thermoplastic film and performing a heat treatment for a relatively short time. That is, the gist of the present invention is as follows. A layer comprising a mixture of 10 to 80% by weight of an acrylic copolymer containing 70% by weight or more of an acrylonitrile unit, 15 to 80% by weight of PVA, and 5 to 50% by weight of an olefin-maleic anhydride copolymer forms a thermoplastic resin film. A gas barrier film formed on at least one side.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail.

The acrylonitrile copolymer used in the present invention contains at least 70% by weight, preferably at least 80% by weight of acrylonitrile, and at most 30% by weight of at least one vinyl monomer copolymerizable therewith. Desirably, it is not more than 20% by weight. Acrylonitrile 70%
If it is less than 30, sufficient gas barrier properties cannot be obtained.

The vinyl monomer copolymerizable with acrylonitrile is not particularly limited, and is a compound having a carbon-carbon unsaturated double bond, such as acrylates, methacrylates, acrylamides, methacrylamides, Acrylates, methacrylates, vinylidenes, and urethanes having an unsaturated bond having a functional group bonded thereto,
Silicones having an unsaturated bond and fluorine-based unsaturated monomers can be used. In particular, unsaturated carboxylic esters,
Specific examples include methyl acrylate, ethyl acrylate,
Butyl acrylate, 2-ethylhexyl acrylate and the like are preferred.

The acrylic copolymer in the present invention can be produced by a known method, but preferably, a method in which an acrylonitrile monomer and another vinyl monomer are emulsion-polymerized in the presence of an emulsifier is used. Can be Examples of the emulsifier include fatty acid soaps, organic sulfonates, PVA, olefin such as methyl vinyl ether-maleic anhydride copolymer, olefin-maleic anhydride copolymer such as isobutylene-maleic anhydride, and polyvinylpyrrolidone. One or a mixture of two or more thereof can be used. The type of polymerization initiator, surfactant and the like are not particularly limited, but since these substances can remain in the coating film formed from the latex and cause deterioration of gas and water vapor barrier properties, the amount of the substance used should be as small as possible. Small amounts are preferred.

The PVA used in the present invention can be obtained by a known method such as complete or partial saponification of a vinyl ester polymer. Examples of the vinyl ester include vinyl formate, vinyl acetate, vinyl propionate, vinyl pivalate, vinyl versatate and the like, with vinyl acetate being most preferred industrially. Other vinyl compounds can be copolymerized with the vinyl ester as long as the effects of the present invention are not impaired. Other vinyl monomers include crotonic acid, acrylic acid, unsaturated monocarboxylic acids such as methacrylic acid and its esters, salts, anhydrides, amides, nitriles, and maleic acid,
Examples include unsaturated dicarboxylic acids such as itaconic acid and fumaric acid and salts thereof, α-olefins having 2 to 30 carbon atoms, alkyl vinyl ethers, and vinylpyrrolidones. In addition, as a saponification method, a known alkali saponification method or acid saponification method can be used, and among them, a method of alcoholysis using an alkali hydroxide in methanol is preferable. PVA having a degree of polymerization of 300 to 3000 can be used. If the degree of polymerization is too low, the gas barrier properties decrease, while if the degree of polymerization is too high, the viscosity of the coating solution becomes too high and handling becomes difficult. Further, the saponification degree is preferably 95% or more, and when it is less than 95%, the gas barrier property decreases.

The olefin used in the present invention
The maleic anhydride copolymer is obtained by polymerizing maleic anhydride and another vinyl compound by a known method such as solution radical polymerization. Examples of the vinyl compound to be copolymerized include alkyl vinyl ethers having 3 to 30 carbon atoms such as methyl vinyl ether and ethyl vinyl ether, methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, butyl acrylate, and methacryl. Acrylates such as butyl acrylate, vinyl esters such as vinyl vinyl formate, p-styrene,
Examples thereof include olefins having 2 to 30 carbon atoms such as p-styrenesulfonic acid, ethylene, propylene, and isobutylene. Of these, alkyl vinyl ethers, lower olefins, and the like are most preferred in terms of improving gas barrier properties. The maleic anhydride units of the polymer used may be partially esterified or amidated.

As a method for preparing a mixed solution of an acrylonitrile copolymer, PVA, and an olefin-maleic anhydride copolymer, a known method may be used using a dissolving vessel equipped with a stirrer or the like. For example, PVA and olefin-maleic anhydride copolymer solids may be sequentially added to and mixed with an acrylonitrile copolymer latex,
A and an aqueous solution of olefin-maleic anhydride copolymer may be separately prepared and added to the acrylonitrile copolymer latex. The fraction of each component in the mixture was 10 to 80% by weight of the acrylonitrile copolymer and 15 to 80% by weight of PVA.
80% by weight of olefin-maleic anhydride copolymer
５０50% by weight. In the polymerization of the acrylonitrile copolymer latex, PVA or an olefin-maleic anhydride copolymer can be used as an emulsifier. In such a case, the amount is determined in consideration of the amount thereof. PV used as emulsifier
A or the olefin-maleic anhydride copolymer and the PVA or the olefin-maleic anhydride copolymer to be mixed later are the same, or the copolymer components, the molecular weight, the degree of saponification, etc. are different. You may.

In the preparation of the mixture, it is possible to add an appropriate amount of another organic or inorganic compound for the purpose of improving properties such as wettability, water resistance and film forming property of the coating agent. At this time, by adding an appropriate amount of an alkali compound to the carboxyl group of the olefin-maleic anhydride copolymer, the gas barrier properties of the obtained film are remarkably improved. In particular, when the pH of the liquid is adjusted in the range of 2.8 to 3.7, the gas barrier property is most improved. Any alkali compound can be used as long as it can neutralize a carboxyl group, such as an alkali metal or alkaline earth metal hydroxide,
Examples include ammonium hydroxide and organic amines.

In the present invention, in addition to the above-described components, an organic or inorganic crosslinking agent which reacts with a hydroxyl group of PVA or a carboxyl group of olefin-maleic anhydride is added to further improve gas barrier properties. It is also possible to make it. Examples of such a crosslinking agent include dialdehyde compounds, diamine compounds, epoxy compounds, isocyanate compounds, melamine compounds, bisoxazoline compounds, carbodiimide compounds, zirconium salts, and polyvalent metal salts.

The gas barrier film of the present invention can be obtained by coating the mixture prepared as described above on at least one surface of a thermoplastic resin film, followed by heating and drying and, if necessary, heat treatment.

The thermoplastic resin film used in the present invention includes polyamide resins such as nylon 6, nylon 66 and nylon 46; polyester resins such as polyethylene terephthalate, polyethylene naphthalate, polybutylene terephthalate and polybutylene naphthalate; polypropylene; Examples include a film made of a polyolefin resin such as polyethylene or a mixture thereof, or a laminate of these films, and may be an unstretched film or a stretched film. In order to improve the coating properties of the coating agent and the adhesion between the coating layer and the film, the film is treated with a corona discharge or a primer containing an adhesive component such as acrylic resin or urethane resin. It can be coated.

As a method for producing a film, a thermoplastic resin is heated and melted by an extruder and extruded from a T-die.
An unstretched film is obtained by cooling and solidifying with a cooling roll or the like, or extruded from a circular die and solidified by water cooling or air cooling to obtain an unstretched film. In the case of producing a stretched film, a method in which the unstretched film is wound once or continuously stretched by a simultaneous biaxial stretching method or a sequential biaxial stretching method is preferable. In view of performance such as mechanical properties and thickness uniformity of the film, a method of combining a flat film forming method using a T-die and a tenter stretching method is preferable.

The thickness of the coat layer in the present invention is at least 0.1 in order to sufficiently enhance the gas barrier properties of the film.
It is desirable that the thickness be greater than 1 μm. The solid content concentration of the mixed solution to be coated is appropriately changed depending on the viscosity and reactivity of the solution and the specifications of an apparatus to be used. However, a layer having a thickness sufficient to exhibit gas barrier properties is used for a solution that is too dilute. Is difficult to coat, and a problem that a long time is required in a subsequent drying step is likely to occur. On the other hand, if the concentration of the solution is too high, problems may occur in the mixing operation, storage stability, and the like. From such a point, the polymer concentration is preferably in the range of 10 to 60% by weight of the whole solution.

The method of coating the film with the mixture is not particularly limited, but includes gravure roll coating,
Conventional methods such as reverse roll coating, wire bar coating, and die coating can be used. The coating may be performed before stretching the film, or may be performed on the stretched film. To perform coating prior to stretching, first coat the unstretched film, dry it, and then supply it to a tenter-type stretching machine to simultaneously stretch the film in the running direction and width direction (simultaneous biaxial stretching) or heat-treat it. Alternatively, the film may be stretched in the running direction of the film using a multi-stage heat roll or the like, coated, dried, and then stretched in the width direction (sequential biaxial stretching) by a tenter-type stretching machine. It is also possible to combine stretching in the running direction with simultaneous biaxial stretching in a tenter. Further, a method of coating before stretching and then performing stretching and heat treatment is a preferable method because a high temperature during stretching and heat treatment can be used for a crosslinking reaction.

The heat treatment is preferably performed in an atmosphere at a temperature of 150 ° C. or more, preferably 180 ° C. or more, in order to cause a crosslinking reaction of the PVA in the coat layer with the crosslinking agent. If the heat treatment temperature is low, the crosslinking reaction cannot proceed sufficiently, and it is difficult to obtain a film having sufficient gas barrier properties.

[0024]

Next, the present invention will be described in detail with reference to examples.

Oxygen permeability 20 ° C., relative humidity 8 using a Mocon oxygen barrier measuring device
The oxygen permeability in a 5% atmosphere was measured. Film-forming properties The surface of the coated film was visually observed, and those without defects such as cloudiness and scratch # were evaluated as good (O), and those with the above defects were evaluated as poor (X).

Example 1 An acrylonitrile copolymer emulsion (Acrylonitrile content: 97% by weight) manufactured by Nippon Exlan Co., Ltd.
The concentration was adjusted to be% by weight to obtain a stock solution (a). On the other hand, PVA (UF040G, manufactured by Unitika Chemical Co., Ltd., degree of saponification: 99%, average degree of polymerization: 400) was dissolved in hot water to obtain a 20% by weight aqueous solution to obtain a stock solution (b). Also, methyl vinyl ether-
Maleic acid equimolar copolymer (International Specialty
Products: GANTREZ AN119) was dissolved in an aqueous solution containing 2 mol% of sodium hydroxide with respect to the carboxyl group to form a 20% by weight solution to obtain a stock solution (c).
The stock solutions (a), (b) and (c) were mixed, and the weight ratio (as solid content) of the acrylonitrile copolymer, PVA, and maleic anhydride copolymer was 30:50:20. This coating solution is dried on a biaxially stretched PET film (Emblet manufactured by Unitika Ltd., thickness 12 μm) to a thickness of about 2 μm after drying.
And dried at 100 ° C. for 2 minutes, and then heat-treated at 200 ° C. for 10 seconds. Table 1 shows the performance of the obtained gas barrier film.

Example 2 220 parts of water was placed in a pressure-resistant reactor lined with glass,
After charging 0.04 parts of sodium persulfate and degassing, the temperature of the contents was kept at 80 ° C. In a separate container, 80 parts of acrylonitrile, 18 parts of methyl acrylate, and 2 parts of methyl methacrylate were mixed and continuously added in the above pressure-resistant reactor over 5 hours. In parallel, 0.6 part of sodium persulfate (added as a 1.48% concentration aqueous solution) and sulfomethacrylate (trade name Ant manufactured by Nippon Emulsifier Co.)
ox MS-2N) (2 parts, added as a 4.76% aqueous solution) was metered in continuously over 5 hours. During this time, the content was maintained at 80 ° C., and the reaction was allowed to proceed until the internal pressure was sufficiently reduced. The solid content of the obtained high nitrile copolymer latex was adjusted to 20% by weight, and the stock solution (a) was prepared.
And Subsequently, the stock solutions (b) and (c) prepared in the same manner as in Example 1 were mixed such that the solid content weight ratio was as shown in Table 1. This coating solution is applied to a biaxially stretched PET film (Emblet PET12, thickness 12
μm), coated with a Meyer bar so that the thickness of the coating film after drying was about 2 μm, and dried at 100 ° C. for 2 minutes.
Heat treatment was performed at 200 ° C. for 10 seconds. The results are shown in Table 1.

Comparative Example 1 An acrylonitrile copolymer was prepared in the same procedure as in Example 2.
The weight ratio of PVA and maleic anhydride copolymer is 90: 5:
5 was prepared and coated on a biaxially stretched PET film, but a uniform coating was not obtained, and the oxygen permeability was 900.
ml / m ² · day · MPa, which was equivalent to an uncoated film.

Examples 3-4, Comparative Examples 2-3 Undiluted solutions (a), (b) prepared by the same procedure as in Example 2,
A coating solution prepared by mixing (c) at the ratio shown in Table 1 was coated in the same manner as in Example 1, dried and heat-treated. The results are shown in Table 1.

Example 5 The same operation as in Example 2 was carried out except that an isobutylene-maleic anhydride copolymer (Kuraray: Isoban) was used as the maleic anhydride copolymer. The results are shown in Table 1.

Example 6 The same operation as in Example 2 was performed except that a styrene-maleic anhydride copolymer (SMA2000 manufactured by Atochem) was used as the maleic anhydride copolymer. The results are shown in Table 1.

Comparative Example 4 In the polymerization of the acrylic copolymer, the same operation as in Example 2 was performed except that the monomer mixing ratio was changed to 60 parts of acrylonitrile, 38 parts of methyl acrylate, and 2 parts of methyl methacrylate. The results are shown in Table 1.

Example 7 Nylon 6 resin was extruded with a T die (75 mm diameter,
Using a gentle compression type single screw with an L / D of 45), extrude it into a sheet at a cylinder temperature of 260 ° C and a T-die temperature of 270 ° C, and closely quench it on a cooling roll adjusted to a surface temperature of 10 ° C. An unstretched film having a thickness of 150 μm was produced. Subsequently, the unstretched film was guided to a gravure roll coater, and the stock solution used in Example 2 was coated so that the coat thickness after drying became 20 μm, and dried in a hot air dryer at 80 ° C. for 30 seconds. Next, the film is supplied to a tenter-type simultaneous biaxial stretching machine, preheated at a temperature of 100 ° C. for 2 seconds, and then longitudinally at 170 ° C. for 3 seconds.
And stretched 3.5 times in the transverse direction. Next, a heat treatment was performed at 200 ° C. for 8 seconds at a lateral relaxation rate of 5%. The results are shown in Table 1.

[0034]

[Table 1]

[0035]

As described above, by using the aqueous coating composition of the present invention, it is possible to obtain a gas barrier film having excellent coating properties and excellent heat barrier properties even under high humidity by heat treatment for a relatively short time after coating. .

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) C08L 35/00 C08L 35/00 // C08J 5/18 CEX C08J 5/18 CEX F-term (reference) 3E086 AD01 BA04 BA15 BA24 BB01 BB22 BB41 CA03 4F071 AA14X AA22X AA29 AA31X AA34X AA36X AF08 AG28 AH04 BB06 BB08 BC02 BC12 4F100 AK01B AK21A AK21C AK25A AK25C AK27A AK27C AK42B AK70A AK70C AL05A AL05C BA03 BA06 BA10A BA10C BA15 EJ38B GB15 GB23 JB16B JD01 JN01 4J002 BB09Y BE02X BG10W BH02Y FD140 GF00 GG02

Claims (2)

[Claims] 1. A mixture comprising 10 to 80% by weight of an acrylic copolymer containing 70% by weight or more of acrylonitrile units, 15 to 80% by weight of polyvinyl alcohol, and 5 to 50% by weight of an olefin-maleic anhydride copolymer. A gas barrier film having a layer formed on at least one surface of a thermoplastic resin film. 2. A laminated film having at least one layer of the gas barrier film according to claim 1.