JP2001310425A - Gas barrier film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a thermoplastic resin film which can have high gas barrier properties even under high humidity. SOLUTION: A gas barrier film forming a coating film comprising 100 pts.wt. polyacrylic acid and 0.1-100 pts.wt. crosslinking agent ingredient such as isocyanate compounds, melamine compounds, urea compounds, epoxy compounds, carboimide compounds and zirconium salt compounds 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 having excellent gas barrier properties even under high humidity.

[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. It may not 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. In addition, 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 collecting the organic solvent. Therefore, there is a problem that the cost increases.

[0006] Various techniques for waterproofing by cross-linking PVA have been conventionally known. For example, it is widely known that a polymer containing a maleic acid unit reacts with a hydroxyl group such as PVA or polysaccharide to be waterproofed. Have been. For example,
JP-A-8-66991 discloses a 25-50% partially neutralized product of isobutylene-maleic anhydride copolymer and PVA.
Is known to have 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.

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 has been proposed in which both polymers are crosslinked by an ester bond by coating the film and heat-treating it (Japanese Patent Application Laid-Open No. 10-237180). However, in this method, the esterification is sufficiently advanced to obtain a gas barrier property of the film. In order to increase the temperature, it is necessary to heat at a high temperature for a long time, and there is a problem in productivity, and the gas barrier property under high humidity is insufficient. Further, the film is colored by reacting at a high temperature for a long period of time, and the appearance is impaired.

[0009]

DISCLOSURE OF THE INVENTION The present inventors have solved the above-mentioned problems and have attempted to provide a barrier film having excellent gas barrier properties even under high humidity and little coloration. .

[0010]

Means for Solving the Problems As a result of earnest studies, the present inventors have found that the above-mentioned problems can be solved by forming a film made of a specific resin composition, and have reached the present invention. That is, the gist of the present invention resides in a gas barrier film in which a coating comprising 100 parts by weight of polyacrylic acid and 0.1 to 100 parts by weight of a crosslinking agent component is formed on at least one surface of a substrate film.

[0011]

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 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.

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 the polyacrylic acid is not particularly limited,
A range of 0000 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, for example, methacrylic acid, methyl acrylate, ethyl acrylate, butyl acrylate, acrylates such as methyl methacrylate, vinyl formate, vinyl esters such as vinyl acetate,
Examples thereof include olefins having 2 to 30 carbon atoms such as styrene, p-styrenesulfonic acid, ethylene, 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 a coating solution for forming a gas barrier film, 0.1 to 20% by weight of carboxyl groups in polyacrylic acid is used.
Is preferably added. Polyacrylic acid has high hydrophilicity and can be made into an aqueous solution without adding an alkali. However, by adding an alkali compound, the gas barrier property of the obtained film is 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 present invention, the gas barrier coating is composed of 0.1 to 1 of a crosslinking agent component per 100 parts by weight of polyacrylic acid.
The composition comprises 00 parts by weight, preferably 0.3 to 70 parts by weight, and more preferably 0.5 to 50 parts by weight.
When the added amount of the crosslinking agent is less than 0.1 part by weight, the crosslinking reaction becomes insufficient, and when it is more than 50 parts by weight, the gas barrier property is rather deteriorated, which is not preferable. The crosslinking agent used in the present invention may be a crosslinking agent having a self-crosslinking property, a compound having a plurality of functional groups which react with a carboxyl group in a molecule, a metal complex having a polyvalent coordination site, or the like. Of these, isocyanate compounds, melamine compounds, urea compounds, epoxy compounds, carbodiimide compounds, zirconium salt compounds, and the like are preferable, and it is particularly preferable to combine an epoxy compound with another crosslinking agent component. Further, a small amount of a catalyst can be added to promote the crosslinking reaction.

The coating solution may be prepared by a known method using a dissolving vessel equipped with a stirrer. At this time, the stability of the aqueous solution is improved by adding the alkali compound to the aqueous solution of polyacrylic acid.

In the present invention, by adding a small amount of a water-swellable layered inorganic compound such as vermiculite, montmorillonite or hectorite to a mixture of polyacrylic acid and a crosslinking agent component, the gas barrier properties of the resulting film are further improved. Can be done.

The gas barrier film of the present invention can be obtained by preparing a mixed solution of polyacrylic acid, coating this on the surface of the film, and drying by heating. Also, after coating on the surface of the film, after preliminary drying,
After stretching in the longitudinal and transverse directions, by heating and drying, a biaxially stretched gas barrier film can be efficiently produced. For the purpose of increasing the solubility of the polyacrylic acid and the crosslinking agent, shortening the drying step, and improving the stability of the solution, a small amount of an alcohol or an organic solvent can be added to water.

In the present invention, the thickness of the gas barrier layer is preferably at least 0.1 μm in order to sufficiently enhance the gas barrier properties of the film.

The concentration of the polymer when the film is coated with a mixed solution comprising polyacrylic acid and a cross-linking agent is appropriately changed depending on the viscosity and reactivity of the solution and the specifications of the equipment to be used. This makes it difficult to coat a layer having a sufficient thickness to exhibit the property, and also tends to cause a problem that a long time is required in a subsequent drying step. 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.

The method for coating the film with the mixed solution 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 accelerate the crosslinking reaction of the gas barrier layer, it is preferable to perform heat treatment in an atmosphere at a temperature of 120 ° C. or more, preferably 150 ° C. or more. 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. 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 1
Seconds or more, preferably 3 seconds or more are good.

[0025]

Next, the present invention will be described in detail with reference to examples. (1) Gas Barrier Property of Film 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 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. The oxygen permeability of the PET film having a thickness of 12 μm was 900 ml / m ² · day · MPa.

Example 1 Polyacrylic acid (Polyacrylic acid 2 manufactured by Wako Pure Chemical Industries, Ltd.)
(5% by weight aqueous solution, number average molecular weight: 150,000) 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. An isocyanate compound dispersion (manufactured by Daiichi Kogyo Seiyaku Co., Ltd., based on 100 parts by weight of the solid content of polyacrylic acid,
Elastron BN-11) was added so that the weight of the isocyanate compound became 10 parts by weight, and the mixture was stirred to obtain a coating liquid. 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 thickness after drying was about 2 μm, and dried at 100 ° C. for 2 minutes. Heat treatment was performed at 200 ° C. for 5 minutes. 20 ° C. of the obtained coated film,
Oxygen permeability at 85% RH is 110 ml / m ² · d
a.MPa, and the oxygen permeability coefficient of the coat layer is 238.
ml · μm / m ² · day · MPa.

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 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 to 9 and Comparative Examples 2 and 3 The same operation as in Example 1 was performed 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.

Examples 10 to 12 As shown in Table 1, the same operation as in Example 1 was carried out except that two kinds of crosslinking agents were used in combination. Table 1 shows the performance of the obtained film.

Example 13 The coating solution obtained in Example 1 was coated on a biaxially stretched nylon film (emblem manufactured by Unitika Ltd., thickness: 15 μm) with a Mayer bar so that the thickness of the coating after drying was about 2 μm. After drying at 100 ° C. for 2 minutes, heat treatment was performed at 200 ° C. for 5 minutes. Table 1 shows the performance of the obtained film.

[0031]

[Table 1]

[0032]

According to the present invention, a film made of polyacrylic acid or a partially neutralized polyacrylic acid and a coating agent in which a crosslinking agent is mixed at a specific ratio is formed on the surface of a thermoplastic resin film, so that the film is excellent even under high humidity. A film having improved gas barrier properties is obtained.

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) B29L 9:00 B29L 9:00 C08L 101: 00 C08L 101: 00 (72) Inventor Hayami Onishi Uji Kyoto Pref. 23 Uji Kozakura Ichika Central Research Laboratory F-term (reference) 4F006 AA35 AA38 AB24 AB33 AB34 AB54 AB65 AB73 BA05 CA07 DA04 4F100 AK25B AK42A AK48A AT00A BA02 CA02B CC01B EH46B EJ37 EJ38A EJ41 GB03 A01A29A QG15 QG18

Claims (6)

[Claims] 1. A gas barrier film in which a coating comprising 100 parts by weight of polyacrylic acid and 0.1 to 100 parts by weight of a crosslinking agent component is formed on at least one surface of a base film. 2. A crosslinking agent component comprising: an isocyanate compound;
The gas barrier film according to claim 1, which is at least one of a melamine compound, a urea compound, an epoxy compound, a carbodiimide compound, and a zirconium salt compound. 3. The gas barrier film according to claim 1, wherein the oxygen permeability coefficient at 20 ° C. and 85% RH is 1000 ml · μm / m ² · day · MPa or less. 4. The gas barrier film according to claim 1, wherein the base film is a nylon 6 film. 5. The gas barrier film according to claim 1, wherein the base film is a polyethylene terephthalate film. 6. An aqueous solution comprising 100 parts by weight of polyacrylic acid and 0.1 to 100 parts by weight of a cross-linking agent component, containing 0.1 to 20 equivalent% of an alkali compound based on a carboxyl group in polyacrylic acid. The gas-barrier film according to any one of claims 1 to 5, which is obtained by coating a base film with an aqueous coating agent mixed with, followed by stretching and heat treatment.