JP4302260B2 - Gas barrier film - Google Patents

Description

【００３７】
【発明の効果】
本発明によれば、高湿度下でも高いガスバリア性を有する熱可塑性樹脂フィルムを工業的に安価に製造することができる。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a gas barrier film having excellent gas barrier properties even under high humidity.
[0002]
[Prior art]
Thermoplastic resin films such as polyamide and polyester are excellent in strength, transparency, and moldability, and are therefore used in a wide range of applications as packaging materials. However, when used for applications that require long-term storage, such as retort-treated foods, higher gas barrier properties are required.
[0003]
In order to improve the gas barrier property, a film in which polyvinylidene chloride (PVDC) is laminated on the surface of a thermoplastic resin film has been widely used for food packaging, etc., but PVDC generates organic substances such as acid gas during incineration. For this reason, in recent years, interest in the environment has increased and there has been a strong demand for a shift to other materials.
[0004]
Polyvinyl alcohol (PVA) is a material that replaces PVDC, which 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 decreases rapidly, and the food containing moisture, etc. In many cases, it cannot be used for packaging.
[0005]
A film made of a copolymer of vinyl alcohol and ethylene (EVOH) is known as a film that improves the deterioration of gas barrier properties under high humidity of PVA, but the gas barrier properties under high humidity are maintained at a practical level. In order to do so, it is necessary to increase the ethylene content to some extent. When EVOH is used as a coating material, it must be dissolved 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 recovery step of the organic solvent. Therefore, there is a problem that the cost becomes high.
[0006]
Various techniques for water resistance by cross-linking PVA with a cross-linking agent have been conventionally known. For example, a polymer containing a maleic acid unit reacts with a hydroxyl group such as PVA or polysaccharide to be water resistant. Widely known. For example, JP-A-8-66991 shows that a layer composed of 25-50% partially neutralized isobutylene-maleic acid copolymer and PVA has excellent water resistance. Japanese Patent Application Laid-Open No. 49-1649 describes a method of making a PVA film water resistant by mixing an alkyl vinyl ether-maleic acid copolymer with PVA.
[0007]
However, water resistance (that is, non-water-solubilization) and gas barrier properties are different, and water-soluble polymers are generally water-resistant by crosslinking molecules, but gas barrier properties are the invasion of relatively small molecules such as oxygen. The gas barrier property is not always obtained by simply crosslinking the polymer. For example, a three-dimensional crosslinkable polymer such as an epoxy resin or a phenol resin does not have a gas barrier property.
[0008]
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, an aqueous solution comprising a partially neutralized product of PVA or polysaccharide and polyacrylic acid or polymethacrylic acid is used. A method of crosslinking both polymers by ester bonds by coating and heat-treating the film has been proposed (Japanese Patent Laid-Open No. 10-237180), but it requires heating at a high temperature for a long time, resulting in a problem in productivity. there were.
[0009]
[Problems to be solved by the invention]
In order to solve the above problems, the present inventors intend to provide a thermoplastic resin film that has a high gas barrier property even under high humidity and can be manufactured industrially at low cost.
[0010]
[Means for Solving the Problems]
As a result of intensive studies, the present inventors have found that the above problems can be solved by forming a layer made of a specific resin composition on the surface of a thermoplastic resin film, and have reached the present invention.
That is, the gist of the present invention is as follows.
The crosslinking agent component is added in an amount of 0.1 to 100 parts by weight of a mixture of 97/3 to 20/80 (weight ratio) of polyvinyl alcohol and an olefin-maleic acid copolymer containing 10 mol% or more of maleic acid units. A gas barrier film having a gas barrier layer formed by heat treatment at a temperature of 150 ° C. or higher after blending 20 parts by weight.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described in detail.
[0012]
Examples of the thermoplastic resin film used in the present invention include 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, and polyethylene. Examples thereof include a film made of a polyolefin resin or a mixture thereof, or a laminate of these films, and may be an unstretched film or a stretched film.
[0013]
As a method for producing a film, a thermoplastic resin is heated and melted by an extruder and extruded from a T die, and is cooled and solidified by a cooling roll or the like to obtain an unstretched film, or is extruded from a circular die and is cooled by water or air. Solidify to obtain an unstretched film.
In the case of producing a stretched film, a method in which an unstretched film is once wound or continuously stretched by a simultaneous biaxial stretching method or a sequential biaxial stretching method is preferable. From the viewpoint of performance such as mechanical properties and thickness uniformity of the film, a method in which a flat film forming method using a T die and a tenter stretching method are combined is preferable.
[0014]
In the present invention, the weight ratio of PVA and olefin-maleic acid copolymer needs to be in the range of 97/3 to 20/80, preferably 90/10 to 40/60. When it is out of this range, it is not possible to obtain a crosslinking density necessary for developing gas barrier properties particularly in a high humidity atmosphere, and it is impossible to obtain a gas barrier film targeted by the present invention.
[0015]
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, etc. Among them, vinyl acetate is industrially most preferable.
[0016]
It is also possible to copolymerize other vinyl compounds with vinyl ester as long as the effects of the present invention are not impaired. Other vinyl compounds include unsaturated monocarboxylic acids such as crotonic acid, acrylic acid, and methacrylic acid and their esters, salts, anhydrides, amides, nitriles, and unsaturated dicarboxylic acids such as maleic acid, itaconic acid, and fumaric acid. Examples thereof include acids and salts thereof, α-olefins having 2 to 30 carbon atoms, alkyl vinyl ethers, vinyl pyrrolidones and the like.
[0017]
In order to form the gas barrier layer in the present invention, it is preferable for production to make the resin composition forming the gas barrier layer water-soluble, and if a large amount of a hydrophobic copolymer component is contained, water-solubility is impaired, which is preferable. Absent.
Further, if the ratio of the vinyl alcohol unit in PVA is too low, the ester bond reaction rate with the maleic acid copolymer is lowered and the gas barrier property of the film is lowered. Therefore, the vinyl alcohol unit is contained in an amount of 40 mol% or more. It is preferable.
[0018]
As the 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.
The closer the saponification degree is to 100%, the better from the viewpoint of gas barrier properties, but there is a concern of gelation when the temperature of the aqueous solution is lowered, and temperature management is necessary for storage. When the degree of saponification is slightly reduced to about 97%, for example, the stability of the solution is remarkably increased and there is almost no decrease in the barrier performance. However, when the degree of saponification is too low, the barrier performance is lowered and the water solubility of the polymer Sex is lost. The preferred degree of saponification is about 80% or more.
[0019]
The olefin-maleic acid copolymer used in the present invention can be obtained by polymerizing maleic anhydride and an olefin monomer by a known method such as solution radical polymerization.
Examples of copolymerizable olefin monomers include alkyl vinyl ethers having 3 to 30 carbon atoms such as methyl vinyl ether and ethyl vinyl ether, methyl (meth) acrylate, ethyl (meth) acrylate, butyl (meth) acrylate, and the like ( Examples include (meth) acrylic acid esters, vinyl esters such as vinyl vinyl acetate, olefins having 2 to 30 carbon atoms such as styrene, p-styrenesulfonic acid, ethylene, propylene, and isobutylene, and a mixture thereof. You can also.
Of these, alkyl vinyl ethers and lower olefins are most preferred from the viewpoint of improving gas barrier properties.
[0020]
In the present invention, the maleic acid unit in the olefin-maleic acid copolymer needs to be contained in an amount of 10 mol% or more.
If the maleic acid unit is less than 10 mol%, the formation of a crosslinked structure due to the reaction with the vinyl alcohol unit in PVA becomes insufficient and the gas barrier property is lowered. Maleic acid may be partially esterified or amidated.
[0021]
In the present invention, the maleic acid unit in the olefin-maleic acid copolymer is likely to have a maleic anhydride structure in which the adjacent carboxyl group is dehydrated and cyclized in a dry state, and the ring opens in wet or aqueous solution to form a maleic acid structure. Become.
[0022]
In this invention, it is necessary to mix | blend 0.1-20 weight part of crosslinking agent components with 100 weight part of the mixture of PVA and an olefin-maleic acid copolymer which forms a gas barrier layer.
By blending the cross-linking agent component, excellent gas barrier properties can be expressed by a short heat treatment.
When the amount of the crosslinking agent is less than 0.1 parts by weight, a sufficient crosslinking effect cannot be obtained, and when it is more than 20 parts by weight, the crosslinking agent adversely inhibits the expression of gas barrier properties.
Examples of the cross-linking agent used in the present invention include a compound containing a plurality of functional groups that react with a hydroxyl group or a carboxyl group in the molecule, or a metal complex having a polyvalent coordination site. Among these, an isocyanate compound, Melamine compounds, epoxy compounds, carbodiimide compounds, zirconium salt compounds and the like are particularly preferable.
[0023]
In the present invention, as a method for forming a gas barrier layer on a thermoplastic film, a coating solution comprising PVA, an olefin-maleic acid copolymer and a crosslinking agent is prepared, coated on the film, dried, and further 150 ° C. or higher. A heat treatment is performed at a temperature of 1 to advance the crosslinking reaction.
[0024]
As a method for adjusting the coating liquid, a known method may be used using a melting pot equipped with a stirrer. For example, a method in which PVA, an olefin-maleic acid copolymer and a crosslinking agent are separately made into an aqueous solution or an aqueous dispersion and mixed before use is preferable. At this time, a small amount of alcohol or an organic solvent can be added to water for the purpose of increasing the solubility, shortening the drying process, improving the stability of the solution, or the like. In addition, a compound serving as a catalyst for the reaction can be added.
[0025]
Furthermore, the gas barrier property of the resulting film can be further improved by adding a small amount of a water-swellable layered inorganic compound such as vermiculite, montmorillonite or hectorite to the resin composition forming the gas barrier layer in the present invention. it can.
[0026]
The thickness of the gas barrier layer in the present invention is desirably at least 0.1 μm in order to sufficiently enhance the gas barrier property of the film.
[0027]
In addition, the polymer concentration when the mixed solution is coated on the film is appropriately changed depending on the viscosity and reactivity of the solution and the specifications of the apparatus, but if it is too dilute, it has a sufficient thickness to exhibit gas barrier properties. It is difficult to coat this layer, and a problem that it takes a long time in the subsequent drying process tends to occur. On the other hand, if the concentration of the liquid is too high, problems may arise in the mixing operation and storage stability. From such a viewpoint, the polymer concentration is preferably in the range of 10 to 50% by weight of the entire solution.
[0028]
The method of coating the mixed solution on the film is not particularly limited, and usual methods such as gravure roll coating, reverse roll coating, wire bar coating, and die coating can be used. Further, the coating may be performed before the film is stretched, or may be performed on the stretched film. At this time, in order to improve the coatability as necessary, the surface of the film is subjected to corona discharge treatment before coating, or an acrylic resin, urethane resin, polyvinyl alcohol resin or the like is coated as a primer layer. Ordinarily known treatments may be performed.
In order to perform coating prior to stretching, the film is first coated on an unstretched film and dried, and then supplied to a tenter-type stretching machine to simultaneously stretch the film in the running direction and the width direction (simultaneous biaxial stretching), or heat treatment, Alternatively, the film may be stretched in the running direction of the film using a multistage hot 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 running direction stretching and simultaneous biaxial stretching with a tenter.
A method of coating prior to stretching, followed by stretching and heat treatment is a preferable method because a high temperature during stretching and heat treatment can be used for the crosslinking reaction.
[0029]
In the present invention, in order to enhance the crosslinking reaction of the gas barrier coat layer, it is necessary to perform heat treatment in an atmosphere at a temperature of 150 ° C. or higher, preferably 180 ° C. or higher.
If the heat treatment temperature is low, the crosslinking reaction cannot be sufficiently advanced, and it becomes difficult to obtain a film having sufficient gas barrier properties.
[0030]
【Example】
Next, the present invention will be specifically described with reference to examples.
[0031]
Oxygen permeability The oxygen permeability in an atmosphere of 20 ° C. and a relative humidity of 85% was measured with an oxygen barrier measuring device manufactured by Mocon.
[0032]
Example 1
PVA (manufactured by Unitika Chemical Co., Ltd., UF040G, saponification degree 99%, average polymerization degree 400) was dissolved in pure water to obtain a 10% by weight aqueous solution.
As an olefin-maleic acid copolymer, an equimolar copolymer of methyl vinyl ether-maleic acid (GANTREZ AN119) manufactured by International Specialty Products was dissolved in an aqueous solution containing 2 mol% sodium hydroxide with respect to the carboxyl group, and 10 weights were obtained. % Solution.
The aqueous solution was mixed so that the weight ratio of PVA and olefin-maleic acid copolymer was 80/20, and then the isocyanate was added to 100 parts by weight of the total solid content of PVA and olefin-maleic acid copolymer. The compound dispersion (Daiichi Kogyo Seiyaku, Elastron BN11) was added so that the weight of the isocyanate compound was 5 parts by weight, and the mixture was stirred to prepare a coating solution.
After coating this coating liquid on a biaxially stretched PET film (Embret PET12 manufactured by Unitika, thickness 12 μm) with a Mayer bar so that the coating thickness after drying is about 2 μm, and drying at 100 ° C. for 2 minutes, Heat treatment was performed at 200 ° C. for 10 seconds.
The oxygen permeability at 20 ° C. and 85% RH of the obtained film was an excellent value of 70 ml / m ² · day · MPa.
[0033]
Comparative Example 1
A coating solution was prepared in the same procedure as in Example 1 without adding a crosslinking agent. This coating solution was coated on a PET film in the same manner as in Example 1, dried and heat-treated.
The performance of the obtained film is shown in Table 1.
[0034]
Examples 2-7, Comparative Examples 2-3
The same operation as in Example 1 was performed except that the type of the olefin-maleic acid copolymer, the crosslinking agent and the composition of the coating agent were changed as shown in Table 1.
The performance of the obtained film is shown in Table 1.
[0035]
Example 8
PVA (manufactured by Unitika Chemical Co., Ltd., UF040G, saponification degree 99%, average polymerization degree 400) was dissolved in pure water to obtain a 10% by weight aqueous solution.
As an olefin-maleic acid copolymer, an equimolar copolymer of methyl vinyl ether-maleic acid (GANTREZ AN119) manufactured by International Specialty Products was dissolved in an aqueous solution containing 5 mol% sodium hydroxide with respect to the carboxyl group, and the weight was 20 weight. % Solution.
The aqueous solution was mixed so that the weight ratio of PVA and the olefin-maleic acid copolymer was 70/30, and then the isocyanate was added to 100 parts by weight of the total solid content of the PVA and the olefin-maleic acid copolymer. The compound dispersion (Daiichi Kogyo Seiyaku, Elastron BN11) was added so that the weight of the isocyanate compound was 5 parts by weight, and the mixture was stirred to prepare a coating solution.
Next, nylon 6 resin was extruded into a sheet shape at a cylinder temperature of 260 ° C. and a T die temperature of 270 ° C. using an extruder equipped with a T die (slow compression type single screw with a 75 mm diameter and L / D of 45). The film was brought into close contact with a cooling roll adjusted to a surface temperature of 10 ° C. and rapidly cooled to obtain an unstretched film having a thickness of 150 μm.
Subsequently, the unstretched film was guided to a gravure roll coater, coated so that the coating thickness after drying was 20 μm, and dried in a hot air dryer at 80 ° C. for 30 seconds. Next, the film was supplied to a tenter simultaneous biaxial stretching machine, preheated at a temperature of 100 ° C. for 2 seconds, and then stretched at 170 ° C. at a magnification of 3 times in the machine direction and 3.5 times in the transverse direction. Next, heat treatment was performed at 200 ° C. for 15 seconds with a transverse relaxation rate of 5%, and after cooling to room temperature, the stretched film was wound up.
The performance of the obtained film is shown in Table 1.
[0036]
[Table 1]

[0037]
【The invention's effect】
According to the present invention, a thermoplastic resin film having a high gas barrier property even under high humidity can be produced industrially at low cost.

Claims (2)

The crosslinking agent component is added in an amount of 0.1 to 100 parts by weight of a mixture of 97/3 to 20/80 (weight ratio) of polyvinyl alcohol and an olefin-maleic acid copolymer containing 10 mol% or more of maleic acid units. A gas barrier film having a gas barrier layer formed by heat treatment at a temperature of 150 ° C. or higher after blending 20 parts by weight.   The gas barrier film according to claim 1, wherein the crosslinking agent component is at least one compound selected from an isocyanate compound, a melamine compound, an epoxy compound, a carbodiimide compound, and a zirconium salt compound.