JP2001105547A - Gas-barrier film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a thermoplastic resin film which has high gas-barrier properties even in a high humidity atmosphere and can be produced inexpensively. SOLUTION: A gas-barrier film having a gas-barrier layer is produced. The gas-barrier layer is formed by a method in which 0.1-20 pts.wt. of a crosslinking agent component is added to 100 pts.wt of a mixture of polyvinyl alcohol and an alkylvinyl ether-maleic anhydride copolymer in a weight ratio of 97/3-20/80, and the mixture is heat-treated.

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 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 (PVDC) is applied to the surface of a thermoplastic resin film.
Has been widely used for food packaging, etc., but PVDC generates organic substances such as acidic gas at the time of incineration, and in recent years, interest in the environment has increased and the shift to other materials has been strongly desired. .

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 a 25-50% partially neutralized product of isobutylene-maleic acid copolymer and PVA has excellent water resistance. Japanese Patent Application Laid-Open No. 49-1649 discloses P
A method is described in which a PVA film is made water-resistant by mixing an alkyl vinyl ether-maleic acid copolymer with VA.

However, water resistance (ie, water insolubility) and gas barrier properties are different properties. Generally, a water-soluble polymer is made water resistant by cross-linking molecules, but the gas barrier property is relatively small, such as oxygen. A property that prevents intrusion and diffusion of molecules, and gas barrier properties are not always obtained by simply cross-linking polymers.For example, three-dimensional cross-linkable polymers such as epoxy resin and phenol resin do not have gas barrier properties .

[0008] A method of coating a film with a liquid composition comprising a water-soluble polymer and exhibiting a high gas barrier property even under a high humidity is based on the use of PVA or polysaccharide and a partially neutralized product of polyacrylic acid or polymethacrylic acid. A method is proposed in which both films are cross-linked by ester bonding by coating a film with an aqueous solution and heat-treating the film (JP-A-10-237180). Had a problem.

[0009]

SUMMARY OF THE INVENTION In order to solve the above problems, the present inventors have attempted to provide a thermoplastic resin film which has high gas barrier properties even under high humidity and can be industrially manufactured at low cost. Is what you do.

[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. Reached. That is, the gist of the present invention is as follows. 97/3 to 20/8 of polyvinyl alcohol and olefin-maleic acid copolymer
A gas barrier film having a gas barrier layer formed by blending 0.1 to 20 parts by weight of a crosslinking agent component with respect to 100 parts by weight of a 0 (weight ratio) mixture and then performing heat treatment.

[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 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.

In the present invention, the weight ratio of PVA to the olefin-maleic acid copolymer must be in the range of 97/3 to 20/80, preferably 90/10 to 40/60. When the ratio is out of this range, the crosslink density required for exhibiting the gas barrier property particularly in a high-humidity atmosphere cannot be obtained, and the gas barrier film intended in the present invention cannot be obtained.

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.

It is also possible to copolymerize the vinyl ester with another vinyl compound 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 esters, salts, anhydrides, amides, and nitriles thereof, 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, and vinylpyrrolidones.

In order to form the gas barrier layer in the present invention, it is preferable from the viewpoint of production that the resin composition forming the gas barrier layer is made water-soluble. When a large amount of a hydrophobic copolymer component is contained, the water solubility is impaired. Is not preferred. If the ratio of the vinyl alcohol unit in the PVA is too low, the ester bond reaction rate with the maleic acid copolymer decreases, and the gas barrier property of the film decreases.
It is preferable that the content of the vinyl alcohol unit is 40 mol% or more.

As the saponification method, a known alkali saponification method or acid saponification method can be used, and among them, a method of alcoholysis using methanol with an alkali hydroxide 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 there is almost no decrease in the barrier performance. Sex is lost. The preferred degree of saponification is about 80% or more.

The olefin used in the present invention
The maleic acid copolymer 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.

In the present invention, the maleic acid unit in the olefin-maleic acid copolymer preferably contains at least 10 mol%. When 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 PVA becomes insufficient, and the gas barrier property is reduced. The maleic acid may be partially esterified or amidated.

In the present invention, the maleic acid unit in the olefin-maleic acid copolymer tends to have a maleic anhydride structure in which adjacent carboxyl groups are dehydrated and cyclized in a dry state. It becomes an acid structure.

In the present invention, it is necessary to add 0.1 to 20 parts by weight of a crosslinking agent component to 100 parts by weight of a mixture of PVA and an olefin-maleic acid copolymer which forms a gas barrier layer. By blending a crosslinking agent component, excellent gas barrier properties can be exhibited by heat treatment for a short time. If the amount of the cross-linking agent is less than 0.1 part by weight, a sufficient cross-linking effect cannot be obtained. If the amount is more than 20 parts by weight, the cross-linking agent adversely inhibits the development of gas barrier properties, which is not preferable. Examples of the crosslinking 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. Melamine compounds, epoxy compounds, carbodiimide compounds, zirconium salt compounds and the like are particularly preferred.

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 dried. Heat treatment is performed at a temperature of 150 ° C. or more to cause a crosslinking reaction to proceed.

The coating liquid may be prepared by a known method using a dissolving vessel equipped with a stirrer. For example, a method is preferable in which PVA, an olefin-maleic acid copolymer, and a crosslinking agent are separately prepared as an aqueous solution or aqueous dispersion, and mixed before use. 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 step, and improving the stability of the solution. Further, a compound serving as a catalyst for the reaction may be added.

Further, 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, the gas barrier properties of the film obtained can be further improved. Can be done.

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 properties of the film.

The concentration of the polymer when the mixed solution is coated on a film is appropriately changed depending on the viscosity and reactivity of the solution and the specifications of the apparatus. It becomes 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 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. At this time, in order to improve the coatability as necessary, the surface of the film is subjected to a corona discharge treatment before coating, or an acrylic resin, a urethane resin, a polyvinyl alcohol resin is coated as a primer layer, etc. Alternatively, a generally known treatment may be performed. 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.

In the present invention, in order to enhance the crosslinking reaction of the gas barrier coat layer, it is preferable to perform heat treatment in an atmosphere at a temperature of 150 ° C. or more, preferably 180 ° 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.

[0030]

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

Oxygen permeability 20 ° C., relative humidity 8 using an oxygen barrier measuring instrument manufactured by Mocon.
The oxygen permeability in a 5% atmosphere was measured.

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. As an olefin-maleic acid copolymer, an equimolar copolymer of methyl vinyl ether-maleic acid (GAN) manufactured by International Specialty Products
TREZ AN119) was dissolved in an aqueous solution containing 2 mol% of sodium hydroxide with respect to the carboxyl group to obtain a 10% by weight solution. The aqueous solution was mixed such that the weight ratio of PVA and the olefin-maleic acid copolymer was 80/20,
Subsequently, the isocyanate compound dispersion liquid (Elastron BN11, manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) is added to PVA and the olefin-maleic acid copolymer in a total amount of 100 parts by weight so that the weight of the isocyanate compound becomes 5 parts by weight. , And stirred to prepare a coating solution. Apply this coating solution to 2
Axial stretched PET film (Emblet PE manufactured by Unitika)
T12, thickness 12μm) on the dried film thickness of about 2μ
m with a Meyer bar and 100 ° C for 2
After drying for 200 minutes, it was heat-treated at 200 ° C. for 10 seconds. The oxygen permeability of the obtained film at 20 ° C. and 85% RH showed an excellent value of 70 ml / 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 7 and Comparative Examples 2 to 3 The same operation as in Example 1 except that the olefin-maleic acid copolymer, the type of the crosslinking agent and the composition of the coating agent were changed as shown in Table 1. Was done. Table 1 shows the performance of the obtained film.

Example 8 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. As an olefin-maleic acid copolymer, an equimolar copolymer of methyl vinyl ether-maleic acid (GAN) manufactured by International Specialty Products
TREZ AN119) was dissolved in an aqueous solution containing 5 mol% of sodium hydroxide with respect to the carboxyl group to obtain a 20% by weight solution. The aqueous solution was mixed such that the weight ratio of PVA and the olefin-maleic acid copolymer was 70/30,
Subsequently, the isocyanate compound dispersion liquid (Elastron BN11, manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) is added to PVA and the olefin-maleic acid copolymer in a total amount of 100 parts by weight so that the weight of the isocyanate compound becomes 5 parts by weight. , And stirred to prepare a coating solution. Next, nylon 6
An extruder equipped with a T die (75 mm diameter, L / D 4
5), extruded in a sheet shape 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 rapidly cooled to a thickness of 150 μm. An unstretched film was used. Subsequently, the unstretched film was guided to a gravure roll coater, coated so as to have a coat thickness after drying of 20 μm, and dried in a hot air dryer at 80 ° C. for 30 seconds. Next, the film was supplied to a tenter-type simultaneous biaxial stretching machine and preheated at a temperature of 100 ° C. for 2 seconds.
The film was stretched at a magnification of 3 times in the machine direction and 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 after cooling to room temperature, the stretched film was wound.
Table 1 shows the performance of the obtained film.

[0036]

[Table 1]

[0037]

According to the present invention, a thermoplastic resin film having high gas barrier properties even under high humidity can be industrially manufactured at low cost.

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification FI FI Theme Court ゛ (Reference) C08L 29:00 C08L 29:00 (72) Inventor Kento Shiba 23 Uji Kozakura, Uji City, Kyoto 23 Unitika Co., Ltd. Central F-term in laboratory (reference) 3E086 AD01 BA04 BA15 BA24 BB01 BB22 BB87 CA03 4F071 AA02 AA14X AA29 AA36X AA76 AE02 AF08 AG12 AH04 BA02 BB02 BC01 4F100 AA27B AA27H AH02B AH03B AH03BB AK03 AK03 AK03

Claims (2)

[Claims] 1. A crosslinking agent component of 0.1 to 2 parts by weight per 100 parts by weight of a 97/3 to 20/80 (weight ratio) mixture of polyvinyl alcohol and an olefin-maleic acid copolymer.
A gas barrier film having a gas barrier layer formed by heat treatment after blending 0 parts by weight. 2. The gas barrier film according to claim 1, wherein the crosslinking agent component is at least one compound among an isocyanate compound, a melamine compound, an epoxy compound, a carbodiimide compound, and a zirconium salt compound.