JP2000289154A - Film with gas barrier property and manufacture thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a film capable of maintaining high gas barrier properties even under high humidity and a method for manufacturing the film industrially at a low cost. SOLUTION: This film with gas barrier properties has a layer comprising a vinyl polymer A containing 40 mol% or more vinyl alcohol unit and a vinyl polymer B containing 10 mol% or more maleic acid or maleic anhydride unit and further, 99/1-40/60 molar ratio between the vinyl alcohol unit of (A) and the maleic acid unit or the maleic anhydride unit of (B), formed on at least one of the faces of the film.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a thermoplastic resin film having excellent gas barrier properties and a method for producing the same.

[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 content of ethylene to some extent, such a polymer is poorly soluble in water, and when a coating material is used, an organic solvent or a mixed solvent of water and an organic solvent is used. However, it is not desirable from the viewpoint of environmental problems, and also requires a step of recovering an organic solvent, which leads to a problem of high cost. .

[0006] 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 cross-linked by an ester bond by coating the film and heat-treating it.
No. 10-237180), this method requires high-temperature and long-time heating in order to sufficiently promote the esterification and sufficiently enhance the gas barrier properties of the film, and there has been a productivity problem.

[0007]

SUMMARY OF THE INVENTION The present invention solves the above-mentioned problems of the prior art and provides a thermoplastic resin film capable of maintaining a high gas barrier property even under high humidity, and an industrially inexpensive film. It is intended to provide a method of manufacturing.

[0008]

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 laminating a specific resin composition on the surface of a film, and have reached the present invention. That is, the gist of the present invention is as follows. (1) A vinyl polymer (A) containing at least one side of a film and containing at least 40 mol% of a vinyl alcohol unit.
And 10 mol% of maleic acid or maleic anhydride units
Containing the vinyl polymer (B) contained above, and
The molar ratio between the vinyl alcohol unit (A) and the maleic acid or maleic anhydride unit (B) is 99/1 to 40/6.
A gas barrier film, wherein a layer having a value of 0 is formed. (2) A vinyl polymer (A) containing at least one side of a film and containing at least 40 mol% of a vinyl alcohol unit.
And 10 mol% of maleic acid or maleic anhydride units
Containing the vinyl polymer (B) contained above, and
The molar ratio between the vinyl alcohol unit (A) and the maleic acid or maleic anhydride unit (B) is 99/1 to 40/6.
The method for producing a gas barrier film according to the above (1), wherein after applying a solution of 0, heat treatment is performed at a temperature of 150 ° C. or more.

[0009]

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

The vinyl alcohol polymer (A) containing at least 40 mol% of a vinyl alcohol unit used in the present invention is a polymer of a vinyl ester or a copolymer of a vinyl ester and another vinyl monomer. Alternatively, it can be obtained by a method of partially saponifying.
Examples of the vinyl ester include vinyl formate, vinyl acetate, vinyl propionate, vinyl pivalate, and vinyl versatate. Of these, vinyl acetate is industrially preferred. Other vinyl monomers to be copolymerized with vinyl esters include crotonic acid, acrylic acid, unsaturated monocarboxylic acids such as methacrylic acid and esters, salts, anhydrides, amides, nitrile compounds, maleic acid, itaconic acid, Unsaturated sulfonic acids such as fumaric acid and salts thereof,
Examples thereof include olefins having 2 to 30 carbon atoms, alkyl vinyl ethers, and vinylpyrrolidones. The above polymer is saponified, and all or a part of the vinyl ester unit becomes a vinyl alcohol unit. As the saponification method, a known alkali saponification method and acid saponification method can be applied, and among them, a method of alcoholysis using an alkali hydroxide in methanol is preferable.

In the present invention, the content of the vinyl alcohol unit in the vinyl alcohol polymer (A) must be 40 mol% or more based on all vinyl group units. If the vinyl alcohol unit is less than 40 mol%, a film having sufficient gas barrier properties cannot be obtained. This is because the hydroxyl group of the vinyl alcohol unit is
In addition to acting as a reactive group that forms a crosslinked structure by reacting with the polymer (B) containing maleic acid or maleic anhydride units, the strong cohesive force of unreacted hydroxyl groups effectively works to enhance gas barrier properties. Because. The most preferred example of the vinyl alcohol-based polymer is polyvinyl alcohol. However, a polymer obtained by copolymerizing a maleic anhydride group or another vinyl-based compound may be used. Further, those obtained by chemically modifying a part of a vinyl alcohol unit can also be used.

The polymer (B) according to the present invention containing maleic acid or maleic anhydride units in an amount of 10 mol% or more.
Is obtained by polymerizing maleic acid or maleic anhydride with another vinyl monomer by a method such as solution radical polymerization. Other vinyl monomers include alkyl vinyl ethers having 3 to 30 carbon atoms, such as methyl vinyl ether and ethyl vinyl ether, acrylates such as methyl acrylate, ethyl acrylate, butyl acrylate, methyl methacrylate, and vinyl formate ,
A vinyl ester such as vinyl acetate, an olefin having 2 to 30 carbon atoms such as styrene, p-styrenesulfonic acid, propylene and isobutylene, and a compound having a reactive group that reacts with a hydroxyl group of the polymer (A) are used. You can also. Specific examples of the polymer (B) include a copolymer of methyl vinyl ether and maleic acid or maleic anhydride, a copolymer of styrene and maleic acid or maleic anhydride, and a copolymer of isobutylene and maleic acid or maleic anhydride. Can be mentioned.

The polymer (B) in the present invention must contain maleic acid or maleic anhydride units in an amount of 10 mol% or more. The maleic acid or maleic anhydride unit in the polymer (B) reacts with the vinyl alcohol unit-containing polymer (A) to form a crosslinked structure, thereby obtaining a high gas barrier property.

In the present invention, the molar ratio of the vinyl alcohol unit in the polymer (A) to the maleic acid or maleic anhydride unit in the polymer (B) is from 99/1 to 40 /.
It must be in the range of 60. If the molar ratio is out of this range, it is not possible to obtain an effective crosslinking density for the expression of gas barrier properties of the film particularly under a high humidity atmosphere, and to obtain a gas barrier film intended for the present invention. Can not.

The gas barrier property of the film is obtained by further adding a small amount of a water-swellable layered inorganic compound such as vermiculite, montmorillonite or hectorite to the layer comprising the polymer (A) and the polymer (B) in the present invention. Can be further improved. Also,
In order to improve the properties of the film, various organic or inorganic additives can be contained in the layer comprising the polymer (A) and the polymer (B) as long as the object of the present invention is not impaired.

The film of the present invention can be obtained by preparing a mixed solution of the polymer (A) and the polymer (B), coating the solution on the surface of the film, and drying by heating. As a solvent for preparing the mixed solution, one or more mixed solvents of solvents such as water, lower alcohol, methyl ethyl ketone, methyl acetate, benzene, and toluene can be used. It is preferable to use water as the solvent in the case of exhibiting the property in view of the environment of the process or the cost of the solvent. However, a method of adding a small amount of an alcohol or an organic solvent to water is effective for the purpose of increasing the solubility, shortening the drying step, and improving the stability of the solution. In order to enhance the gas barrier properties of the film of the present invention, the polymer (A) and the polymer (B)
It is necessary that a cross-linking reaction by an ester bond occurs between them, but a catalyst such as an acid can be added to accelerate the cross-linking reaction.

In the present invention, the thickness of the layer comprising the polymer (A) and the polymer (B) 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 film is coated with the mixed solution composed of the polymer (A) and the polymer (B) is appropriately changed depending on the viscosity and the reactivity of the liquid and the specifications of the apparatus to be used. With a solution, it becomes difficult to coat a layer having a sufficient thickness to exhibit gas barrier properties, 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 70% by weight of the whole solution.

The method for coating the film with the mixed solution comprising the polymer (A) and the polymer (B) is not particularly limited, but a usual method such as gravure roll coating, reverse roll coating, wire bar coating and the like can be used. The coating may be performed before stretching the film, or may be performed on the stretched film.

In the present invention, the polymer (A) and the polymer (B) formed on one or both sides of the film are used.
In order to cause a cross-linking reaction between the two polymers, it is preferable to perform the heat treatment at a temperature of 150 ° C. or more after coating. If the temperature of the heat treatment is low, the crosslinking reaction cannot proceed sufficiently, making it difficult to obtain a film having sufficient gas barrier properties. Also,
The method of performing 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 the crosslinking reaction.

In the present invention, as a base film on which a layer composed of the polymer (A) and the polymer (B) is formed, polyamide resins such as nylon 6, nylon 66 and nylon 46, polyethylene terephthalate (PET),
Polyester resin such as polyethylene naphthalate, polybutylene terephthalate, polybutylene naphthalate,
A film made of a polyolefin resin such as polypropylene or polyethylene, or a mixture thereof, or a laminate of those films is used, and may be an unstretched film or a stretched film.

[0021]

Next, the present invention will be described in detail with reference to examples. The oxygen barrier property of the film was determined by measuring the oxygen permeability in an atmosphere at 20 ° C. and a relative humidity of 85% using an oxygen barrier measuring instrument manufactured by Mocon.

Example 1 UF040G (99.6% of saponification degree, average polymerization degree: 500) manufactured by Unitika Chemical Co., Ltd. was used as PVA, and as a maleic anhydride copolymer, an International Specialty Pr.
GANTREZ AN119 (a molar copolymer of methyl vinyl ether / maleic anhydride) manufactured by Oducts Co. was used.
First, PVA was dissolved in pure water to obtain a 10% by weight aqueous solution. On the other hand, GANTREZ was added to maleic acid unit at 1
Dissolve in an aqueous solution containing 0 mol% sodium hydroxide
% By weight. Subsequently, both aqueous solutions were mixed so that the molar ratio of the vinyl alcohol unit in PVA and the maleic acid unit of GANTREZ was as shown in Table 1, and stirred at room temperature to prepare a coating solution. This coating solution is applied to a biaxially stretched PET film (Emblet PE manufactured by Unitika).
T12, thickness 12 μm), the coating thickness after drying is about 2
It was coated with a wire bar to a thickness of μm, dried at 100 ° C. for 2 minutes, and then heat-treated at 200 ° C. for 5 minutes. The oxygen permeability of the obtained film is as shown in Table 1,
It had excellent gas barrier properties.

Examples 2 and 3 Coated films were prepared in the same manner as in Example 1 except that the mixing ratio of PVA and GANTREZ was changed as shown in Table 1. Table 1 shows the oxygen permeability of the obtained film.

Example 4 As a maleic anhydride copolymer, an equimolar copolymer of styrene and maleic anhydride (SMA1000 manufactured by Atochem) was used.
Was used to prepare a 10% by weight aqueous solution of SMA 1000 containing 10 mol% of sodium hydroxide based on maleic anhydride units. Next, this solution and the same PV as in Example 1 were used.
A solution was prepared by mixing vinyl alcohol units of PVA with SMA10.
The mixture was mixed such that the ratio of maleic anhydride units of 00 was 80/20. In the same manner as in Example 1, biaxially stretched PE
The film was coated on a T film, and the results of measuring the oxygen permeability of the obtained film are shown in Table 1.

Example 5 As a maleic anhydride copolymer, a styrene-maleic anhydride copolymer (SMA2000 manufactured by Atochem Co., Ltd .; maleic anhydride unit content: 33 mol%) was used. Biaxially stretched PET was prepared in the same manner as in Example 4 except that mol% of sodium hydroxide was added.
The film was coated, and the results of measuring the oxygen permeability of the obtained film are shown in Table 1.

Example 6 An ethylene-vinyl alcohol copolymer (EVOH) having an ethylene content of 27 mol% was prepared by mixing water / isopropanol = 35 /
It was dissolved in 65 parts by weight to obtain a 10% by weight solution of EVOH. On the other hand, GANTREZ was set to 1 in the same manner as in Example 1.
A 0% by weight aqueous solution was obtained. Next, the two solutions were mixed so that the molar ratio of the vinyl alcohol unit in EVOH to the maleic acid unit in GANTREZ was 80/20, and the mixture was stirred at room temperature to prepare a coating solution. This coating solution was used in Example 1.
The film was coated on a biaxially stretched PET film in the same manner as described above, and the results of measuring the oxygen permeability of the obtained film are shown in Table 1.

Example 7 In the same manner as in Example 1, a 10% by weight aqueous solution of PVA was prepared. On the other hand, as a maleic anhydride copolymer, an isobutylene-maleic anhydride equimolar copolymer (Isovan 04 manufactured by Kuraray Co., Ltd.) was used, and 60 parts per maleic anhydride unit was used.
10% by weight of isoban containing mol% sodium hydroxide
An aqueous solution was prepared. The two solutions were mixed, and the two solutions were mixed such that the ratio of the vinyl alcohol unit of PVA to the maleic anhydride unit of isovan became 80/20, and stirred at room temperature to prepare a coating solution. This coating solution was coated on a biaxially stretched PET film in the same manner as in Example 1, and the results of measuring the oxygen permeability of the obtained film are shown in Table 1.

Comparative Example 1 A 10% by weight aqueous solution of PVA as in Example 1 was prepared and coated on a biaxially stretched PET film by the same method as in Example 1, and the oxygen permeability of the obtained film was measured. The results are shown in Table 1.

COMPARATIVE EXAMPLE 2 GANTRTE to vinyl alcohol unit of PVA
A biaxially stretched PET film was coated in the same manner as in Example 1 except that the molar ratio of maleic acid units of Z was changed to 20/80, and the results of measuring the oxygen permeability of the obtained film are shown in Table 1. Indicated.

Comparative Example 3 A biaxially stretched PET film was coated in the same manner as in Example 1 except that the ratio of the vinyl alcohol unit of PVA to the maleic anhydride unit of SMA1000 was changed to 20/80. Table 1 shows the results of measuring the oxygen permeability of the sample.

[0031]

[Table 1]

[0032]

According to the present invention, a film capable of maintaining a high gas barrier property even under a high humidity without generating an organic substance such as an acid gas at the time of incineration as in the case of PVDC, and an industrially applicable film. Is provided at a low cost, and its practical value is extremely large.

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Yoshihiro Umemura 23 Uji Kozakura, Uji-shi, Kyoto Unitika Central Research Laboratory F-term (reference) 4F006 AA12 AA35 AA39 AB20 AB24 BA05 CA07 DA04 EA05 4F100 AK21B AK24B AK42A AL01B AL05B AS00A BA02 EH462 EJ38A EJ422 GB90 JD02 JD03 YY00 4J038 CB091 CB092 CB131 CB132 CC021 CC022 CC091 CC092 CE021 CE022 CE051 CE052 CF061 CF062 CG081 CG082 CG141 CG142 CH031 CH032 CJ09 CJ08MA08 MA08

Claims (3)

[Claims] 1. A film comprising a vinyl polymer (A) containing 40 mol% or more of vinyl alcohol units and at least one maleic acid or maleic anhydride unit on at least one surface of the film.
It contains a vinyl polymer (B) containing 0 mol% or more, and the molar ratio of the vinyl alcohol unit of (A) to the maleic acid or maleic anhydride unit of (B) is 99/1.
A gas barrier film, comprising a layer having a thickness of 40/60. 2. The gas barrier film according to claim 1, wherein the oxygen permeability measured at 20 ° C. and 85% RH is 150 ml / m ² · day · MPa or less. 3. A film comprising a vinyl polymer (A) containing at least 40 mol% of a vinyl alcohol unit and at least one maleic acid or maleic anhydride unit on at least one surface of the film.
It contains a vinyl polymer (B) containing 0 mol% or more, and the molar ratio of the vinyl alcohol unit of (A) to the maleic acid or maleic anhydride unit of (B) is 99/1.
The method for producing a gas barrier film according to claim 1 or 2, wherein a heat treatment is performed at a temperature of 150 ° C or higher after applying an aqueous solution of ４０40/60.