JP2001335736A - Coating agent and film for gas barrier - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a gas barrier coating agent exhibiting excellent gas barrier properties even at a high humidity and a gas barrier film having a layer formed from the coating agent on at least one side of a thermoplastic resin film. SOLUTION: This coating agent is an aqueous one which contains (A) a vinyl polymer having at least 40 mol% vinyl alcohol units, (B) an olefin-maleic acid copolymer having at least 10 mol% maleic acid or anhydride units, and (C) an inorganic layered compound provided that the wt. ratios of A/B and (A+B)/C are (97/3)-(20/80) and (10,000/1)-(1/2), respectively.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a gas-barrier coating agent having excellent gas-barrier properties even under high humidity, and a gas-barrier film obtained by forming the same on at least one surface of a thermoplastic resin film.

[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, moldability and gas barrier properties. 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 replacing PVDC, polyvinyl alcohol (PVA) does not generate toxic gas and has a high gas barrier property under a low humidity atmosphere. However, as the humidity increases, the gas barrier property rapidly decreases and contains moisture. In many cases, it cannot be used for packaging foods.

A film made of a copolymer of vinyl alcohol and ethylene (EVOH) is known as a film in which the gas barrier property of PVA under a high humidity is reduced, but the gas barrier property under a high humidity is practically used. In order to maintain the level, 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.

Various techniques for making PVA water-resistant by cross-linking PVA with a cross-linking agent are known in the art. For example, a polymer containing a maleic acid unit is made water-resistant by reacting with hydroxyl groups such as PVA and polysaccharides. It is widely known. For example, Japanese Patent Application Laid-Open No. 8-66991 discloses that a layer composed of 25-50% partially neutralized isobutylene-maleic anhydride copolymer and PVA has excellent water resistance. JP-A-49-1649 describes a method of making a PVA film water-resistant by mixing an alkyl vinyl ether-maleic anhydride copolymer with PVA.

However, water resistance (ie, water insolubility) and gas barrier properties are different properties. Generally, water resistance is achieved by cross-linking polymer molecules. However, gas barrier properties do not allow penetration of relatively small molecules such as oxygen. The gas barrier property is not always obtained simply by crosslinking the polymer. For example, a three-dimensional crosslinkable polymer such as an epoxy resin or a phenol resin does not have the gas barrier property.

Further, a method has been proposed in which an aqueous solution comprising PVA and a partially neutralized product of polyacrylic acid or polymethacrylic acid is coated on a film and heat-treated, whereby both polymers are crosslinked by an ester bond. Opening 1
In this method, long-time heating at a high temperature is required in order to sufficiently promote esterification and enhance the gas barrier property of the film, and there is a problem in productivity. Further, the film is colored by prolonged reaction at a high temperature, and the appearance is impaired.

Also, a method has been proposed in which a resin composition comprising a carboxyl group-containing high hydrogen bonding resin, a hydroxyl group-containing high hydrogen bonding resin, and an inorganic layered silicate is modified with heat and active energy rays (Japanese Patent Application Laid-Open No. Hei 10 (1999)). 231434), which requires an active energy ray, which requires further improvement from the viewpoint of economy.

[0010]

In order to solve the above problems, the present inventors have provided a highly reactive barrier coating agent having improved productivity, and provided this coating agent with a thermoplastic resin film. It is intended to provide a barrier film having high gas barrier properties even under high humidity and little coloring by applying it on at least one surface of the film.

[0011]

Means for Solving the Problems As a result of intensive studies, the present inventors have found that a coating agent containing a specific resin composition is applied to the surface of a film to form a layer composed of this resin composition. The present inventors have found that the above-mentioned problems can be solved and arrived at the present invention. That is, the gist of the present invention is as follows. (1) A vinyl polymer (A) containing at least 40 mol% of vinyl alcohol units, an olefin-maleic acid copolymer (B) containing at least 10 mol% of maleic acid or maleic anhydride units, and an inorganic layered compound In the aqueous coating agent containing (C), the weight ratio of (A) and (B) is 97/3 to 20/80, and (A + B) / (C) =
A gas barrier coating agent having a weight ratio of 10,000 / 1 to 1/2. (2) A gas barrier film in which a layer comprising the coating agent according to the above (1) is formed on at least one surface of a thermoplastic resin film.

[0012]

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

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.

As a method for producing a film, a thermoplastic resin is heated and melted by an extruder and extruded from a T-die and solidified by cooling with a cooling roll or the like to obtain an unstretched film, or extruded from a circular die and cooled with water or It is solidified by 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 the mechanical properties of the film and the uniformity of the thickness, a method of combining a flat film forming method using a T-die and a tenter stretching method is preferable.

Further, in order to improve the adhesiveness between the film and the coat layer, the film surface may be subjected to a corona discharge treatment or an anchor coat.

In the present invention, the vinyl polymer (A)
And the olefin-maleic acid copolymer (B) has a weight ratio of 9
7/3 to 20/80, preferably 90/10 to 25 /
It must be in the range of 75. When the ratio is out of this range, the crosslink density necessary for exhibiting the gas barrier property of the film particularly in a high humidity atmosphere cannot be obtained, and the gas barrier film intended in the present invention cannot be obtained.

The coating agent in the present invention is preferably water-soluble in terms of production, and if a hydrophobic copolymer component is contained in a large amount, the water-solubility is impaired, which is not preferable. Also,
The vinyl alcohol unit in the vinyl polymer (A) is 4
It is necessary that the content is 0 mol% or more, and if this ratio is too low, the ester bond reaction rate with the maleic acid copolymer (B) decreases, and the gas barrier film aimed at by the present invention is obtained. Can not.

A typical compound of the vinyl polymer (A) used in the present invention is polyvinyl alcohol. Polyvinyl alcohol can be obtained using 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.

As the saponification method, a known alkali saponification method or acid saponification method can be used. Among them, a method of alcoholysis using an alkali hydroxide in methanol is preferable. The degree of saponification is preferably closer to 100% from the viewpoint of gas barrier properties, but there is a concern that the aqueous solution may be gelled when the temperature of the aqueous solution is lowered, and temperature control is required for storage. When the saponification degree is slightly reduced, for example, to about 97%, the stability of the solution is remarkably increased, and the barrier performance is hardly reduced. However, when the saponification degree is too low, the barrier performance is reduced, and the water solubility of the polymer is reduced. Sex is lost. The preferred degree of saponification is about 80% or more.

Next, the olefin-maleic acid copolymer (B) used in the present invention is obtained by polymerizing maleic anhydride and an olefin monomer by a known method such as solution radical polymerization. Examples of the copolymerizable olefin monomer include alkyl vinyl ethers having 3 to 30 carbon atoms such as methyl vinyl ether and ethyl vinyl ether, and methyl (meth) acrylate, ethyl (meth) acrylate, and butyl (meth) acrylate. (Meth) acrylic acid esters, vinyl esters such as vinyl vinyl formate, styrene, p-styrenesulfonic acid, olefins having 2 to 30 carbon atoms such as ethylene, propylene and isobutylene, and mixtures thereof are used. You can also. Of these, alkyl vinyl ethers, lower olefins, and the like are most preferred in terms of improving gas barrier properties.

The maleic acid unit in the polymer (B) in the present invention must be contained in an amount of 10 mol% or more. If the amount of the maleic acid unit is less than 10 mol%, the formation of a crosslinked structure by the reaction with the vinyl alcohol unit in the polymer (A) is insufficient, and the gas barrier property is reduced.
Further, the maleic acid unit may be partially esterified or amidated.

The polymer (B) used in the present invention
The maleic acid unit in the dry state easily becomes a maleic anhydride structure in which adjacent carboxyl groups are dehydrated and cyclized, and opens into a maleic acid structure when wet or in an aqueous solution.

The inorganic layered compound in the present invention is an inorganic compound in which unit crystal layers overlap to form a layered structure, and preferably swells and cleaves in a solvent.

Examples of the inorganic layered compound include montmorillonite, beidellite, saponite, hectorite, sauconite, vermiculite, fluoromica, muscovite, paragonite, phlogopite, biotite, lepidrite, margarite, clintnite, anandite, chlorite, donba Site, sudoite, cocoaite, clinochlore, shamosite, nimite, tetrasilyl mica, talc, pyrophyllite, nacrite, kaolinite, halloysite, chrysotile, sodium teniolite,
Zansophyllite, antigorite, dickite, hydrotalcite and the like are mentioned, and swellable fluoromica and montmorillonite are particularly preferred.

These inorganic layered compounds may be naturally occurring, artificially synthesized or modified, or may be those treated with an organic substance such as an onium salt.

The swellable fluoromica-based mineral is most preferable because of its excellent transparency, and is represented by the following formula. α (MF) · β (aMgF ₂ · bMgO) · γSiO ₂ (where M represents sodium or lithium, α, β,
γ, a and b each represent a coefficient, and 0.1 ≦ α ≦ 2, 2 ≦ β
≦ 3.5, 3 ≦ γ ≦ 4, 0 ≦ a ≦ 1, 0 ≦ b ≦ 1, a + b
= 1. )

As a method for producing such a swellable fluoromica-based mineral, for example, silicon oxide, magnesium oxide and various fluorides are mixed, and the mixture is heated at a temperature of 1400 to 1500 ° C. in an electric furnace or a gas furnace. There is a so-called melting method in which the mica is completely melted in the range and the fluorine mica-based mineral grows in the reaction vessel during the cooling process.

There is also a method of using talc as a starting material and intercalating an alkali metal ion into the starting material to obtain a swellable fluoromica-based mineral (Japanese Patent Laid-Open No. 2-14).
9415). In this method, a swellable fluoromica-based mineral can be obtained by mixing talc with an alkali silicofluoride or alkali fluoride and subjecting the mixture to a short-time heat treatment at about 700 to 1200 ° C. in a magnetic crucible.

At this time, the amount of alkali silicate or alkali fluoride mixed with talc is 10 to 10% of the whole mixture.
It is preferable that the content be in the range of 35% by weight. If the content is outside this range, the yield of the swellable fluoromica-based mineral decreases, which is not preferable.

The alkali metal of alkali silicate or alkali fluoride is preferably sodium or lithium. In the step of producing the swellable fluoromica-based mineral, it is also possible to adjust the swellability of the resulting swellable fluoromica-based mineral by adding a small amount of alumina.

In addition, among the inorganic layered compounds that can be used in the present invention, montmorillonite is represented by the following formula and can be obtained by purifying naturally occurring compounds. MaSi ₄ (Al _2-a Mg _a ) O ₁₀ (OH) ₂ .nH ₂ O (where M represents a sodium cation, and a represents 0.2
5 to 0.60. Further, the number of water molecules bonded to the ion-exchangeable cations between the layers can be changed according to conditions such as the type of cation and humidity, and is represented by nH ₂ O in the formula. Also, montmorillonite includes the same type ion-substituted magnesia montmorillonite, iron montmorillonite, and iron magnesia montmorillonite represented by the following formula group, and these may be used. MaSi ₄ (Al _1.67-a Mg _{0.5 + a} ) O ₁₀ (OH) ₂ .n
_{H 2 O MaSi 4 (Fe 2} -a 3+ Mg a) O 10 (OH) 2 · nH 2 O MaSi 4 (Fe 1.67-a 3+ Mg 0.5 + a) O 10 (OH) 2 ·
nH ₂ O (where M represents a cation of sodium and a represents 0.2
5 to 0.60. )

Normally, montmorillonite has ion-exchangeable cations such as sodium and calcium between its layers, but the content ratio varies depending on the place of production. In the present invention, it is preferable that the ion-exchangeable cation between the layers is replaced with sodium by an ion-exchange treatment or the like. It is preferable to use montmorillonite purified by water treatment.

In the resin composition constituting the coating agent of the present invention, a heat stabilizer, an antioxidant, a reinforcing material, a pigment, a deterioration inhibitor, a weathering agent, a flame retardant, and the like, as long as their properties are not significantly impaired. Plasticizers, release agents, lubricants and the like may be added.

Examples of the heat stabilizer, antioxidant and deterioration inhibitor include hindered phenols, phosphorus compounds, hindered amines, sulfur compounds, copper compounds, halides of alkali metals, and mixtures thereof.

As the reinforcing agent, for example, clay, talc,
Calcium carbonate, zinc carbonate, wollastonite, silica,
Alumina, magnesium oxide, calcium silicate, sodium aluminate, sodium aluminosilicate, magnesium silicate, glass balloon, carbon black, zinc oxide, zeolite, hydrotalcite, metal fiber, metal whisker, ceramic whisker, potassium titanate whisker, boron nitride , Graphite, fiberglass,
And carbon fiber.

The gas barrier properties of a film obtained by adding a small amount of a crosslinking agent component to the coating agent in the present invention can be further improved.

As a crosslinking agent, an isocyanate compound,
Melamine compounds, epoxy compounds, carbodiimide compounds, zirconium salt compounds and the like can be mentioned.

The coating solution may be prepared by a known method using a dissolving vessel equipped with a stirrer, and a known device such as a homogenizer, a ball mill, or a high-pressure dispersion device may be used as the stirrer. it can. At this time, the stability of the aqueous solution is improved by adding the alkali compound to the aqueous solution of the polymer (B).

The gas barrier film of the present invention is obtained by preparing a mixed solution of the polymer (A), the polymer (B) and the inorganic layered compound (C), coating the solution on the surface of the film, and drying by heating. . For the purpose of increasing the solubility, shortening the drying step, and improving the stability of the solution, a small amount of alcohol or an organic solvent can be added to water.

In the present invention, the thickness of the layer comprising the polymer (A), the polymer (B) and the inorganic layer compound (C) is desirably at least 0.1 μm in order to sufficiently enhance the gas barrier properties of the film. .

The polymer concentration at the time of coating the film with the coating agent solution can be appropriately changed depending on the viscosity and reactivity of the solution and the specifications of the apparatus used. However, it is difficult to coat a layer having a sufficient thickness, 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 viewpoint, the polymer concentration is preferably in the range of 10 to 50% by weight of the whole solution.

The method of coating the film with the solution is not particularly limited, but ordinary methods such as gravure roll coating, reverse roll coating, and wire bar coating can be used. 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.

In the present invention, in order to cause a cross-linking reaction of the gas barrier layer, the temperature is 120 ° C. or higher, preferably 150 ° C.
It is preferable to perform heat treatment in an atmosphere at a temperature of not less than ° C. If the heat treatment temperature is low, the crosslinking reaction cannot proceed sufficiently,
It becomes difficult to obtain a film having sufficient gas barrier properties. If the heat treatment time is too short, the crosslinking reaction cannot proceed sufficiently, and it becomes difficult to obtain a film having sufficient gas barrier properties. Usually, it is 1 second or more, preferably 3 seconds or more.

[0044]

Next, the present invention will be described in detail with reference to examples. In the present invention, since the gas barrier property of the film changes depending on the type and thickness of the base film and the thickness of the coat layer, the oxygen permeability coefficient of the coat layer itself was evaluated.
The oxygen permeability coefficient was determined by the following equation. 1 / QF = 1 / QB + L / PC where QF: oxygen permeability of the coated film (ml / m
² · day · MPa) QB: Oxygen permeability of the thermoplastic resin film (ml / m ²⁾
・ Day ・ MPa) PC: Oxygen permeability coefficient of coat layer (ml ・ μm / m ²・ d
ay · MPa) L: Coat layer thickness (μm) Therefore, if PC and L are known, the oxygen permeability of the coat film can be estimated from the above equation. Oxygen barrier properties were measured at 20 ° C using a Mocon oxygen barrier measuring instrument.
The oxygen permeability in an atmosphere with a relative humidity of 85% was measured. The oxygen permeability of a PET film having a thickness of 12 μm is 900 ml / m ² · day · MPa,
μm nylon 6 film has an oxygen permeability of 400 ml /
m ² · day · MPa.

Example 1 As a polymer (A), polyvinyl alcohol UF040G (99% saponification degree, average polymerization degree 400) manufactured by Unitika Chemical Co., Ltd. was dissolved in pure water to obtain a 20% by weight aqueous solution. International Specialty Pr as polymer (B)
Gantrez AN119, an equimolar copolymer of methyl vinyl ether-maleic acid manufactured by Oducts Co., Ltd., was dissolved in an aqueous solution containing 2 mol% of sodium hydroxide based on the carboxyl group to form a 20% by weight solution. The two aqueous solutions were mixed so that the weight ratio of the polymer (A) and the polymer (B) was 70/30, and then montmorillonite (Kunimine F, manufactured by Kunimine Kogyo Co., Ltd.) was mixed with the solid content of (A) and (B). It was added so as to be 10% by weight based on the total amount, and stirred to prepare a coating solution. This coating solution was coated on a biaxially stretched PET film (Emblet PET12 manufactured by Unitika Ltd., thickness 12 μm) with a Mayer bar so that the coating film thickness after drying was about 2 μm, and dried at 100 ° C. for 2 minutes. Heat treatment was performed at 200 ° C. for 15 seconds. 20 ° C., 85 of the obtained film
% RH is 26 ml / m ² · day ·
MPa and an excellent value.

Examples 2 to 6 The same operation as in Example 1 was carried out by changing the kind of the inorganic layer compound (C) and the composition of the coating agent. Table 1 shows the oxygen permeability of the obtained film.

Comparative Example 1 A coating solution was prepared in the same procedure as in Example 1 without adding the inorganic layered compound (C). This coating solution was coated on a PET film, dried and heat-treated in the same manner as in Example 1.
The resulting film has an oxygen permeability of 145 ml / m ² · d
ay · MPa.

Comparative Examples 2-3 A coating solution was prepared in the same procedure as in Example 1 except that either the polymer (A) or the polymer (B) was not added. This coating solution was coated on a PET film, dried and heat-treated in the same manner as in Example 1. The obtained film was dissolved in water during the rubbing test.

Example 7 Coating was carried out under the conditions shown in Table 1 using an isobutylene-maleic anhydride copolymer (Isovan manufactured by Kuraray Co., Ltd.) as the polymer (B). The results are shown in Table 1.

Example 8 An extruder (75 mm diameter,
Using a gentle compression type single screw with an L / D of 45), extruded into a sheet at a temperature of 260 ° C. and a T-die temperature of 270 ° C., closely adhered to a cooling roll adjusted to a surface temperature of 10 ° C., and quenched. And an unstretched film having a thickness of 150 μm. Subsequently, the unstretched film was guided to a gravure roll coater, and the coating solution shown in Example 1 was coated so that the coating thickness after drying was 2 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 15 seconds at a transverse relaxation rate of 5%, and a biaxially stretched film having a thickness of 15 μm was wound. Table 1 shows the oxygen permeability of the obtained film and the oxygen permeability coefficient of the coat layer.

Example 9 Using the coating solution of Example 7, a nylon film was coated in the same manner as in Example 8. Table 1 shows the oxygen permeability of the obtained film and the oxygen permeability coefficient of the coat layer.

Comparative Example 4 A nylon film was coated in the same manner as in Example 8 except that no inorganic layer compound was added. Table 1 shows the oxygen permeability of the obtained film and the oxygen permeability coefficient of the coat layer.

[0053]

[Table 1]

[0054]

By forming the coating agent of the present invention on the surface of a thermoplastic resin film, a film having excellent gas barrier properties can be produced, and excellent gas barrier properties can be maintained even under high humidity. be able to.

Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat II (Reference) C09D 123/00 C09D 123/00 135/00 135/00 (72) Inventor Sayami Onishi 23 Uji Kozakura, Uji-city, Kyoto Prefecture Unitika F-term in the Central Research Laboratories of the Company (reference)

Claims (6)

[Claims] 1. A vinyl polymer (A) containing at least 40 mol% of vinyl alcohol units, an olefin-maleic acid copolymer (B) containing at least 10 mol% of maleic acid or maleic anhydride units, and inorganic In the aqueous coating agent containing the layered compound (C), the weight ratio of (A) and (B) is 97/3 to 20/80, and (A +
B) / (C) = 10000/1 to 1/2 (weight ratio). 2. The gas barrier coating agent according to claim 1, wherein 0.1 to 20% by weight of an alkali compound is mixed with respect to the carboxyl group in the vinyl polymer (B). 3. A gas barrier film in which a layer comprising the coating agent according to claim 1 is formed on at least one surface of a thermoplastic resin film. 4. The gas barrier film according to claim 3, wherein the oxygen permeability coefficient at 20 ° C. and 85% RH is 300 ml · μm / m ² · day · MPa or less. 5. The gas barrier film according to claim 3, wherein the thermoplastic resin film is nylon 6. 6. The gas barrier film according to claim 3, wherein the thermoplastic resin film is polyethylene terephthalate.