JP2001164174A - Gas-barrier coating agent and gas-barrier film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a gas-barrier film which has a high gas-barrier property even under a high humidity and is industrially inexpensively prepared. SOLUTION: The gas-barrier film is prepared by applying a gas-barrier coating agent containing 100 pts.wt. mixture containing a polyvinyl alcohol and a polyacrylic acid at a weight ratio of from 90/10 to 5/95 and from 0.1 to 50 pts.wt. at least one crosslinking agent component chosen from an isocyanate compound, a melamine compound, a urea compound, an epoxy compound, a carbodiimide compound and a zirconate compound onto at least one side of a thermoplastic resin film and heating this.

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 having excellent gas barrier properties even under high humidity and a gas barrier coating agent.

[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 crosslinking with a crosslinking agent are known in the art. For example, a polymer containing a maleic acid unit is reacted with a hydroxyl group of PVA or polysaccharide to make it water-resistant. 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.

By the way, a mixture of PVA and polyacrylic acid or a partially neutralized product thereof is composed of a water-absorbing material, a dispersion stabilizer,
Widely used as thickeners, paper and fiber treatment agents, and the like. P
By coating the film with a mixture of VA and polyacrylic acid or a partially neutralized product thereof, a film having excellent gas barrier properties can be obtained under low humidity, but the hydrophilicity of the coating layer is high under high humidity. In addition, the gas barrier properties are greatly reduced.

As a method of coating a film with a liquid composition comprising a water-soluble polymer and exhibiting high gas barrier properties even under high humidity, an aqueous solution comprising PVA and a partially neutralized product of polyacrylic acid or polymethacrylic acid is used. A method of coating a film and heat-treating the film has been proposed (Japanese Patent Application Laid-Open No. 10-237180). Time heating was required, and there was a problem in productivity. In addition, the film is colored by reacting at high temperature for a long time, and the appearance is impaired.
In particular, when used for food packaging, improvement was required.

[0010]

SUMMARY OF THE INVENTION The present inventors have solved the above-mentioned problems by improving the productivity by providing a highly reactive barrier coating agent and applying the coating agent. Accordingly, it is an object of the present invention to provide a gas barrier film which has high gas barrier properties even under high humidity, has little coloring, and can be industrially manufactured at low cost.

[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 that the weight ratio of polyvinyl alcohol to polyacrylic acid is 90/10
100 parts by weight of a 5/95 mixture and 0.1 parts of the crosslinker component.
A gas barrier coating agent containing 1 to 50 parts by weight, and a film formed on at least one surface of a thermoplastic resin film with the coating agent.

[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.
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 the mechanical properties and thickness uniformity of the film, a method combining a flat film forming method using a T-die and a tenter stretching method is preferable.

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.

As long as the effects of the present invention are not impaired, another vinyl compound can be copolymerized with the vinyl ester. Other vinyl monomers include crotonic acid,
Unsaturated monocarboxylic acids such as 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 and salts thereof, having 2 to 30 carbon atoms Α-olefins, alkyl vinyl ethers, vinyl pyrrolidones and the like.

In the present invention, the polymer to be laminated to impart gas barrier properties to the film surface is preferably water-soluble for production. If a large amount of a hydrophobic copolymer component is contained, the water solubility is impaired. Not preferred.

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. If the saponification degree is too low, the gas barrier performance will decrease. Degree of saponification is usually about 9
0% or more, preferably 95% or more, and the average degree of polymerization is 20%.
0 to 2500, preferably 200 to 2000.

Next, the polyacrylic acid used in the present invention is obtained by polymerizing an acrylic acid monomer by a known method such as solution radical polymerization. Although the number average molecular weight of polyacrylic acid is not particularly limited,
The range of ~ 200,000 is preferred.

A small amount of another vinyl compound can be copolymerized with polyacrylic acid as long as the effects of the present invention are not impaired. Other vinyl compounds include, for example, acrylates such as methacrylic acid, methyl acrylate, ethyl acrylate, butyl acrylate, methyl methacrylate, vinyl esters such as vinyl formate and vinyl acetate, styrene, p-styrene Sulfonic acid, ethylene,
Examples thereof include olefins having 2 to 30 carbon atoms such as propylene and isobutylene, and compounds having a reactive group that reacts with a hydroxyl group or a crosslinking agent of PVA.

In the present invention, when preparing an aqueous solution by mixing PVA and polyacrylic acid, it is preferable to add 0.1 to 20 equivalent% of an alkali compound to the carboxyl group in polyacrylic acid. Polyacrylic acid itself has high hydrophilicity and can be made into an aqueous solution without adding an alkali, but by adding an appropriate amount of an alkali compound, the gas barrier properties of the obtained film are remarkably improved. The alkali compound may be any as long as it can neutralize a carboxyl group in polyacrylic acid, and examples thereof include hydroxides of alkali metals and alkaline earth metals, ammonium hydroxide, and organic ammonium hydroxide compounds.

In the coating agent of the present invention, it is necessary to add 0.1 to 50 parts by weight of a crosslinking agent component to 100 parts by weight of a mixture of PVA and polyacrylic acid which forms a gas barrier layer. . By blending the crosslinking agent component,
The reaction proceeds due to the heat treatment for a short time, excellent gas barrier properties can be exhibited, and the coloring of the film is remarkably improved. When the amount of the crosslinking agent is less than 0.1 part by weight, a sufficient crosslinking effect cannot be obtained, and when the amount is more than 50 parts by weight, the crosslinking agent adversely inhibits the development of gas barrier performance. Absent.

The crosslinking agent used in the present invention may be a crosslinking agent having a self-crosslinking property, such as a compound having a plurality of functional groups in the molecule which react with a hydroxyl group or a carboxyl group, or a metal having a polyvalent coordination site. A complex or the like may be used. Of these, isocyanate compounds, melamine compounds,
Epoxy compounds, carbodiimide compounds, zirconium salt compounds and the like are particularly preferred. Further, the crosslinking agent component
More than one kind may be added.

In the present invention, a small amount of a catalyst may be added in order to promote a crosslinking reaction in the coat layer.

The coating liquid may be adjusted by a known method using a dissolving vessel equipped with a stirrer or the like. For example, a method in which PVA and polyacrylic acid are separately prepared as aqueous solutions and mixed before use is preferable. At this time, the stability of the aqueous solution is improved by adding the alkali compound to the aqueous solution of polyacrylic acid. In addition, when adding PVA and polyacrylic acid to water in a dissolving vessel, it is better to add alkali first.

The gas barrier properties 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 coating agent of the present invention.

The gas barrier film of the present invention is made of PVA
And a mixed solution of polyacrylic acid and a cross-linking agent component is prepared, coated on the surface of the film, and then dried by heating. A small amount of an alcohol or an organic solvent can be added to water for the purpose of enhancing the solubility of each component, shortening the drying step, and improving the stability of the solution.

The thickness of the coat layer of the gas barrier film in the present invention 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 of the present invention can be appropriately changed depending on the viscosity and reactivity of the liquid and the specifications of the apparatus to be used. It becomes difficult to make the thickness sufficient to develop, and a problem that a long time is required in the 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 for coating the film with the coating agent is not particularly limited, but ordinary methods such as gravure roll coating, reverse roll coating, and wire bar coating can be used. In order to perform coating prior to stretching, first, an unstretched film is coated and dried, and then supplied to a tenter-type stretching machine to stretch the film simultaneously in the running direction and the width direction (simultaneously 2 times).
Axial stretching), heat-treated, or stretched in the running direction of the film using a multi-stage hot roll or the like, then coated, dried, and then stretched in the width direction by a tenter-type stretching machine (sequential biaxial stretching). Is also good. 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. On the other hand, 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. The coating agent of the present invention has a high cross-linking agent reacting with PVA or polyacrylic acid or a self-crosslinking reaction of the crosslinking agent even under relatively mild heat treatment conditions of, for example, 200 ° C. for 1 minute or less. High barrier properties can be exhibited even under humidity.

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.

[0033]

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

The oxygen barrier property was determined by measuring the oxygen permeability in an atmosphere at 20 ° C. and a relative humidity of 85% using an oxygen barrier measuring device manufactured by Mocon Corporation. The oxygen permeability coefficient of the coat layer was determined as Qc by measuring the oxygen permeability of the coat film in an atmosphere of 20 ° C. and a relative humidity of 85% using an oxygen barrier measuring device manufactured by Mocon Corporation. On the other hand, the oxygen permeability of the uncoated film was measured, and was determined as QB. Next, the coat thickness was determined from the difference between the average thickness of the uncoated film and the average thickness of the coated film, and was defined as L. From the above values, the oxygen permeability coefficient of the coat layer was calculated using the above equation. In addition, thickness 12 μm
Oxygen permeability of PET film is 900ml / m ² · d
ay · MPa.

Example 1 PVA (UF040G, manufactured by Unitika Chemical Co., Ltd., saponification degree: 99%, average polymerization degree: 400) was dissolved in pure water to obtain a 10% by weight aqueous solution. Polyacrylic acid (manufactured by Wako Pure Chemical Industries, Ltd., polyacrylic acid 25% by weight aqueous solution, number average molecular weight 1)
50,000) was diluted with an aqueous solution containing 10 mol% of sodium hydroxide based on the carboxyl group of polyacrylic acid to obtain a 10% by weight aqueous solution. The aqueous solution was mixed so that the weight ratio of PVA and polyacrylic acid was 30/70, and then the isocyanate compound dispersion (Daiichi Kogyo Seiyaku) was added to 100 parts by weight of the total solid content of PVA and polyacrylic acid. Co., Ltd., Elastron BN-11) was added so that the weight of the isocyanate compound was 5 parts by weight, and stirred to obtain a coating solution. This coating solution is applied to a biaxially stretched PET film (Emblet PET12 manufactured by Unitika Ltd., 12 μm thick).
m) Coating with a Mayer bar so that the thickness of the dried coating film becomes about 2 μm, and drying at 100 ° C. for 2 minutes.
Heat treatment was performed at 00 ° C. for 30 seconds. The appearance of the obtained coated film was good without coloring, and the oxygen permeability at 20 ° C. and 85% RH was 110 ml / m ² · day · MPa.
And the oxygen permeability coefficient of the coat layer is 238 ml / m ² ·
It was day · MPa.

Comparative Example 1 A coating agent was prepared in the same procedure as in Example 1 without adding a crosslinking agent. This coating solution was subjected to PET in the same manner as in Example 1.
The film was coated, dried and heat treated. Table 1 shows the performance of the obtained film.

Examples 2 and 3 The same operation as in Example 1 was performed except that the weight ratio between PVA and polyacrylic acid was changed as shown in Table 1. Table 1 shows the performance of the obtained film.

Examples 4 to 12, Comparative Examples 2 and 3 The same operation as in Example 1 was carried out except that the kind and amount of the crosslinking agent and the degree of neutralization were changed as shown in Table 1. Table 1 shows the performance of the obtained film.

[0039]

[Table 1]

[0040]

According to the present invention, a film made of PVA, polyacrylic acid or partially neutralized polyacrylic acid, and a coating agent obtained by mixing a cross-linking agent at a specific ratio is formed on the surface of a thermoplastic resin. Thus, a film having excellent gas barrier properties can be obtained. In addition, the coating agent of the present invention is suitable for industrial production because a dense crosslinked structure is formed by a short-time heat treatment, and the obtained gas barrier film is excellent in commercial value without coloring.

Continued on the front page (51) Int.Cl. ⁷ Identification code FI Theme coat II (reference) // C08L 29:04 C08L 29:04 Z 33:06 33:06 F term (reference) 4F071 AA29 AA32 AB13 AC06 AC12 AE02 AE19 AF08 AG12 AH04 BA02 BB02 BC02 4F100 AA02A AA02H AH02A AH02H AH03A AH03H AK01B AK21A AK25A AK42B AK48B AL05A AT00B BA02 CA02A CC00A GB23 JB16B JD02A JD03 JL02 JN28 B021

Claims (7)

[Claims] 1. A gas barrier coating agent comprising 100 parts by weight of a mixture of polyvinyl alcohol and polyacrylic acid in a weight ratio of 90/10 to 5/95, 0.1 to 50 parts by weight of a crosslinking agent component, and an aqueous solvent. 2. The crosslinking agent component comprises at least one of an isocyanate compound, a melamine compound, a urea compound, an epoxy compound, a carbodiimide compound, and a zirconia salt compound.
The gas barrier coating agent according to claim 1, which is a compound of a kind. 3. The gas barrier coating agent according to claim 1, wherein an alkali compound is mixed in an amount of 0.1 to 20 equivalent% with respect to a carboxyl group in acrylic acid. 4. A gas barrier film comprising a coating formed on at least one surface of a thermoplastic resin film, wherein the coating comprises the coating agent according to any one of claims 1 to 3. 5. The gas barrier film according to claim 4, wherein the oxygen permeability coefficient at 20 ° C. and 85% RH is 1000 ml · μm / m ² · day · MPa or less. 6. The gas barrier film according to claim 4, wherein the thermoplastic resin film is nylon 6. 7. The gas barrier film according to claim 4, wherein the thermoplastic resin film is polyethylene terephthalate.