WO2000061369A1 - Gas barrier film and process for producing the same - Google Patents

Abstract

A film with gas barrier properties which comprises a thermoplastic resin film and formed on at least one side thereof a coating layer comprising a vinyl polymer (A) comprising at least 40 mol% vinyl alcohol units and a vinyl polymer (B) comprising at least 10 mol% maleic acid units. The (A)/(B) weight ratio is from 97/3 to 20/80. The coating layer has a coefficient of oxygen permeability of 500 ml. νm/m2/day/MPa or lower. This film has high gas barrier properties even under high-humidity conditions.

Description

 Description Gas barrier film and method for manufacturing the same

 The present invention relates to a gas barrier film having a coating layer formed thereon and a method for producing the same. Background art

 Thermoplastic resin films such as polyamides and polyesters are used in a wide range of applications as packaging materials because of their excellent strength, transparency and moldability. However, when used for applications requiring long-term storage, such as retorted foods, higher gas barrier properties are required.

 In order to improve gas barrier properties, films in which polyvinylidene chloride (PVDC) is laminated on the surface of these thermoplastic resin films have been widely used for food packaging and the like. However, since PDCC generates organic substances such as acid gas when incinerated, there is a strong demand for the transfer to other materials as interest in the environment increases in recent years.

 As an alternative to PVDC, polyvinyl alcohol (PVA) does not generate toxic gases and has high gas barrier properties in low-humidity atmospheres. However, PVA often cannot be used for packaging water-containing foods and the like because the gas barrier property rapidly decreases as the humidity increases.

Reduced the gas barrier property of PVA under high humidity by using another material As a good film, a copolymer of vinyl alcohol and ethylene

A film consisting of (E V 0 H) is known. However, in order to maintain the gas barrier properties under high humidity at a practical 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. For this reason, it is not desirable from the viewpoint of environmental problems, and there is a problem that the cost is high because a recovery step of the organic solvent is required.

 There have been known various techniques for achieving water resistance by cross-linking naturally water-soluble PVA using a cross-linking agent.For example, a polymer containing maleic acid units reacts with hydroxyl groups such as PVA and polysaccharides. It is widely known that it is water resistant. For example, JP-A-8-66991 states that a layer consisting of a 25 to 50% partially neutralized isobutylene-maleic acid copolymer and PVA has excellent water resistance. It is shown. JP-A-49-16949 describes a method for making a PVA film water-resistant by mixing an alkyl vinyl ether-maleic acid copolymer with PVA.

 However, water resistance (ie, water insolubility) and gas barrier properties are different properties. In general, water-soluble polymers are made water-resistant by crosslinking molecules. However, gas barrier properties prevent the penetration and diffusion of relatively small molecules such as oxygen, and simply cross-linking a polymer does not always provide gas barrier properties. For example, three-dimensional crosslinkable polymers such as epoxy resin and phenol resin do not have gas barrier properties.

A liquid composition consisting of a water-soluble polymer is coated on a film, As a method of exhibiting high gas barrier properties even under humidity, an aqueous solution consisting of PVA or polysaccharide and a partially neutralized product of polyacrylic acid or polyacrylic acid is coated on a film and heat-treated. Thus, a method has been proposed in which both polymers are crosslinked by an ester bond (jP—A—10—23718). In this method, gas barrier properties are developed by highly advanced cross-linking by an esterification reaction. However, this requires long-time heating at a high temperature, which causes a problem in productivity.

Disclosure of the invention

 The present invention provides a gas barrier film in which a coating agent capable of exhibiting high gas barrier properties even under high humidity is applied to at least one surface of a thermoplastic resin film, and The aim is to provide a method that can be industrially manufactured at low cost. The present inventors have assiduously studied and, as a result, have found that the above-mentioned problems can be solved by laminating a coating agent composed of a specific resin composition on the film surface and heat-treating the same, and have reached the present invention.

 The gist of the present invention is as follows.

(1) A gas barrier film comprising a vinyl polymer (A) containing at least 40 mol% of vinyl alcohol units and a vinyl polymer (B) containing at least 10 mol% of maleic acid units co one Bok layer containing preparative provided on one side at least of a thermoplastic resin film Lum, (a) and (B) the mass ratio of 9 7 / ^/ 3-2 0 da 8 0 Deari, Coat The oxygen permeability coefficient of the layer is not more than 500 m 1 · / m ² / day / MPa.

(2) The vinyl polymer (A) is polyvinyl alcohol. (3) Vinyl polymer (B) force One electrode of methyl vinyl ether-maleic anhydride copolymer, ethylene-maleic anhydride copolymer, and isobutylene-maleic anhydride copolymer Or a mixture thereof.

 (4) The crosslinking agent is contained in the range of 0.1 to 20 parts by mass relative to the total of 100 parts by mass of the vinyl polymer (A) and the vinyl polymer (B).

 (5) The cross-linking agent is a melamine compound or an isocyanate compound.

 (6) The water-swellable inorganic stratiform compound is contained in the range of 0.1 to 50 parts by mass with respect to a total of 100 parts by mass of the vinyl polymer (A) and the vinyl polymer (B). .

 (7) The water-swellable inorganic layered compound is fluorine mica.

 (8) An acrylic copolymer containing 70% by mass or more of acrylonitrile units based on a total of 100 parts by mass of the vinyl polymer (A) and the vinyl polymer (B). It is contained in a range of 200 parts by mass or less.

(9) The oxygen permeability coefficient of the coating layer is not more than 250 ml-11 m / ^mz / day ZMPa.

 (10) The thermoplastic resin is nylon 6.

(11) Oxygen permeability is below 180 ml Zm ² Z day ZM Pa (15 m equivalent of nylon film).

 (12) The thermoplastic resin is polyethylene terephthalate.

(1 3) Oxygen permeability ^{2 5 0 ml Zm 2 / day} / MP a ( poly ethylene terephthalate, single Tofui Lum 1 2 m equivalent) or less.

(14) The gas bath described in any of (1) to (13) above A method for producing a rear film, characterized by applying a coating agent on at least one side of the film and then performing a heat treatment at a temperature of 150 ° C. or more.

 (15) After the coating agent is applied to the film, the film is stretched in at least one of the longitudinal and transverse directions of the film, and then heat-treated.

 (16) Simultaneous biaxial stretching is performed as stretching.

 (17) When stretching after applying the coat layer to the film, the moisture content of the coat layer immediately before stretching is 0.1 to 50% by mass.

 (18) Irradiate the heat-treated film with an electron beam.

 (19) A vinyl polymer which forms a coating agent (B) a methyl vinyl ether-maleic anhydride copolymer, wherein 0.1 to a carboxyl group in the vinyl polymer (B) is used. Contains ~ 20% equivalent of alkaline compound.

 (20) The pH force of the coating agent is in the range of 2.8 to 3.7.

 Therefore, according to the present invention, a coating agent comprising a mixture of a polymer containing vinyl alcohol units in a predetermined ratio or more and a polymer containing maleic anhydride units in a predetermined ratio or more is coated on a film and heat-treated. A thermoplastic resin film having high gas barrier properties even under humidity can be industrially manufactured at low cost.

BEST MODE FOR CARRYING OUT THE INVENTION

 (the film)

As the film used in the present invention, a thermoplastic resin film is suitable. Examples of the film include polyamide resin such as Nylon 6, Nylon 66, and Nylon 46, and polyethylene ethylene. Futari Polyester resin such as polyester, polyethylene naphtholate, polybutylene terephthalate, polybutylene terephthalate, polyolefin resin such as polypropylene, polyethylene, etc., or a film thereof, or a film thereof. Laminate. This film may be an unstretched film or a stretched film.

 This film can be produced by heating or melting a thermoplastic resin with an extruder, extruding it through a T-die, and cooling and solidifying it with a cooling roll to obtain an unstretched film. There is a method in which an unstretched film is obtained by extruding a plastic resin from a circular die and solidifying it by water cooling or air cooling. In the case of producing a stretched film, it is preferable that the film is stretched by a simultaneous biaxial stretching method or a sequential biaxial stretching method after winding the unstretched film once or continuously with the process of producing the unstretched film. From the viewpoint of performance such as mechanical properties and thickness uniformity of the film, a method in which a flat type film forming method using a T-die and a tensile stretching method are preferred.

 (Composition of coating agent)

 The coating layer constituting the gas barrier film of the present invention contains a vinyl polymer (A) containing a vinyl alcohol unit and a vinyl polymer (B) containing a maleic acid unit.

 Among them, a vinyl-based polymer (A) containing a vinyl alcohol unit (hereinafter sometimes simply referred to as “polymer (A)”) is a polymer of a vinyl ester or a vinyl ester and another vinyl-based monomer. Can be obtained by completely or partially saponifying the copolymer of

Vinyl esters include vinyl formate, vinyl acetate, and propion Examples thereof include vinyl acid, vinyl pivalate, and vinyl versatate. Among them, vinyl acetate is industrially preferable.

 Other vinyl monomers to be copolymerized with vinyl esters include unsaturated monocarboxylic acids such as crotonic acid, acrylic acid, and methyl acrylate, and esters, salts, anhydrides, amides, and nitriles thereof. And unsaturated dicarboxylic acids such as maleic acid, itaconic acid and fumaric acid and salts thereof, α-olefins having 2 to 30 carbon atoms, alkyl vinyl ethers, vinyl pyrrolidone and the like.

 The above polymer is saponified and all or a part of the vinyl ester group becomes a vinyl alcohol unit. Known methods for the alcoholic acid saponification and the acid-genation can be used as the method for the salification. Among them, the method of alcoholysis using methanol in methanol is preferable, and the degree of saponification is 10. It is preferable from the viewpoint of gas barrier properties that the value is close to 0%, but when the saponification degree is close to 100%, there is a concern that the aqueous solution may gel when the temperature of the aqueous solution becomes low. Management is required. If the degree of saponification is slightly reduced to, for example, about 97%, the stability of the solution is remarkably increased, and the barrier performance is hardly reduced. However, if the degree of saponification is too low, the barrier performance decreases. The preferred degree of saponification is about 80% or more.

The content of vinyl alcohol units in the vinyl polymer (III) must be at least 40 mol% based on all vinyl group units. When the content of the vinyl alcohol unit is less than 40 mol%, a film having a sufficient gas barrier property cannot be obtained. This is because the hydroxyl group of the vinyl alcohol unit acts as a reactive group that forms a crosslinked structure by reacting with the vinyl polymer (反 応) containing the maleic acid unit. Not only that, the strong cohesive force of unreacted hydroxyl groups in the vinyl alcohol unit works effectively to enhance gas barrier properties.

 The most preferred example of the vinyl-based polymer (A) is polyvinyl alcohol (hereinafter referred to as “PVA”), but copolymers of water-free maleic acid groups or other vinyl-based polymers may also be used. Good, or a partially modified vinyl alcohol unit may be used.

 A vinyl polymer (B) containing maleic acid units (hereinafter sometimes simply referred to as “polymer (B)”) is prepared by a known method such as solution radical polymerization of maleic anhydride and another vinyl monomer. It is obtained by polymerizing with.

 Other vinyl monomers include alkyl vinyl ethers having 3 to 30 carbon atoms, such as methyl vinyl ether and ethyl vinyl ether, methyl (meth) acrylate, ethyl (meth) acrylate, and (meth) acrylyl. (Meth) acrylic acid esters such as butyl acid, vinyl esters such as vinyl vinyl formate, styrene, p-styrenesulfonic acid, and C2-C30 olefins such as ethylene, propylene and isobutylene, etc. Is mentioned. These mixtures can also be used.

 Of these, alkyl vinyl ethers and lower olefins are the most preferable in terms of improving gas barrier properties. Among them, methyl vinyl ether-maleic anhydride copolymer, isobutylene-maleic anhydride copolymer, ethylene The maleic anhydride copolymer is excellent.

Maleic phosphate units in the polymer (B) is a this Toga必¹ is 1 0 mol% or more. If the content of maleic acid units is less than 10 mol%, poly The formation of the crosslinked structure by the reaction with the vinyl alcohol unit in the monomer (A) is insufficient, and the gas barrier property is reduced. The maleic acid may be partially esterified or amidated, and a part of the carboxyl group of the maleic acid may be neutralized by an alkali compound.

 When preparing a liquid coating agent by mixing the polymer (A) and the polymer (B), an appropriate amount of an alcohol compound is added to the carboxyl group in the polymer (B) to stabilize the liquid. Properties and the performance of the coated film can be improved. The amount of the alkali compound to be added should be appropriately selected depending on the type and blending amount of the polymer to be used. In particular, when a methyl vinyl ether-maleic anhydride copolymer is used as the polymer (B), the alkali compound is added. It is preferable to add the compound in an amount of 0.1 to 20% equivalent to the lipoxyl gas of the polymer (B) and adjust the pH of the solution to 2.8 to 3.7. By doing so, the gas barrier properties of the obtained film are remarkably improved.

 According to the present invention, it is necessary to coat the thus prepared coating agent on a film, dry it, and further perform a heat treatment to advance a crosslinking reaction. According to the study of the present inventors, it was found that when the pH of the solution was adjusted to 2.8 to 3.7, the gas barrier property was improved by a very short heat treatment, which is extremely industrially advantageous. It has been found.

Any alkali compound may be used as long as it can neutralize the carboxyl group in the polymer (B), such as hydroxides of alkali metals and alkaline earth metals, ammonium hydroxide, and organic amines. Is mentioned. The maleic acid units in the polymer (B) are adjacent carbohydrates in the dry state. The xyl group is liable to become a maleic anhydride structure dehydrated and cyclized, and when wet or in an aqueous solution the ring is opened to form a maleic acid structure.

 In the coating layer formed on the surface of the film by the coating agent, the composition ratio of the polymer (A) containing a vinyl alcohol unit and the polymer (B) containing a maleic acid unit is expressed by mass. It is necessary that the ratio be in the range of 97/3 to 20/80. Outside of this range, the gas barrier properties of the film will be insufficient, especially in a high humidity atmosphere.

 (Crosslinking agent)

 By including a crosslinking agent in a range of 0.1 to 20 parts by mass with respect to a total of 100 parts by mass of the polymer (A) and the polymer (B), high gas burrs can be obtained even by a very short heat treatment. Can be expressed.

 If the amount of the cross-linking agent is less than 0.1 part by mass, a sufficient cross-linking effect cannot be obtained.If the amount is more than 20 parts by mass, the cross-linking agent acts as an inhibitor of gas barrier properties, resulting in gas barrier properties. Will decrease.

 Examples of such a cross-linking agent include a compound containing a plurality of functional groups that react with a hydroxyl group or a carboxyl group in a molecule or a metal complex having a polyvalent coordination site. Of these, preferred are an isocyanate compound, a melamin compound, an epoxy compound, a carbodiimide compound, a silyl group-containing compound, a zirconium salt compound and the like.

 (Inorganic layered compound)

By adding a water-swellable layered inorganic compound to the mixture of the polymer (A) and the polymer (B), the gas barrier property of the obtained film can be further improved. The term “inorganic layered compound” as used herein refers to an inorganic compound in which unit crystal layers overlap to form a layered structure. Preferred examples of the inorganic layered compound include montmorillonite, pidelite, savonite, hectolite, sauconite, vermiculite, fluoromica, muscovite, paragonite, phlogopite, biotite, levy dry , Margarite clintonite, anandite, chlorite, donpasite, suidoite, cookeite, clinocroix, shamosite, nimaito, tetrasiririkmai power, evening Rek, non-filo-light, nacryate, force-origin, eightloite, chrysotile, sodium teniolite, zansofilite, anti-golite, date kite, hide mouth talcite, etc. Swellable fluoromica or montmorillonite is particularly preferred.

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

 Among the inorganic layered compounds, swellable fluoromica-based minerals are most preferred in terms of transparency. This swellable fluoromica-based mineral is represented by the following formula and can be easily synthesized by a known production method.

(MF) · β (a M g F 2 - b M g O). During · r S i O _z (wherein, M represents fire na Application Benefits um or lithium, beta §, a and b each coefficient Represents 0.1 ≤ α ≤ 2, 2 ≤ β ≤ 3.5, 3 ≤ r ≤ 4, 0 ≤ a ≤ 1 <0 ≤ b ≤ 1, a + b = l.)

The compounding amount of these inorganic layered compounds is preferably from 0.1 to 50 parts by mass. If the amount is less than 0.1 part by mass, the effect of improving gas barrier properties is insufficient. Conversely, if the amount is more than 50 parts by weight, gas barrier properties are further enhanced. When the layered silicate becomes difficult to disperse evenly in the coating liquid, the performance of the coating layer becomes uneven, and the flexibility of the obtained gas barrier film is reduced. Problems are more likely to occur in various processing steps for packaging materials such as.

 (Acrylonitrile copolymer)

 In the present invention, an acrylic copolymer containing 70% by mass or more of an acrylonitrile unit is added to 200 parts by mass of the total of the polymer (A) and the polymer (B). When contained in a range of not more than part by mass, the liquid properties of the coating agent can be improved.

 The coating agent composed of the polymer (A) and the polymer (B) has a high viscosity of the liquid and may be restricted in use depending on the production equipment. However, if the concentration of the solution is too low as a countermeasure, it takes a long time to dry the coating film after coating the coating agent on the film, which is undesirable because the productivity is lowered. Generally, a coating agent having a high concentration and a low viscosity is generally preferred.

 In order to improve this, a possible method is to add a water-dispersible component to the coating agent. Addition of an aqueous dispersion such as general acrylic latex or vinyl acetate-based latex will result in a gas barrier. This is not preferred because the properties are reduced.

 Acryl-based copolymers containing 70% by mass or more of acrylonitrile units have excellent gas barrier properties and can be added to a coating agent consisting of polymer (A) and polymer (B). Thus, the viscosity of the coating agent can be reduced without lowering the gas barrier properties.

The acrylonitrile copolymer contains acrylonitrile in an amount of 70% by mass or less, desirably 80% by mass or more, and the rest is acrylonitrile. One or more vinyl monomers copolymerizable with nitrile are 30% by mass or less, preferably 20% by mass or less. If the acrylonitrile content of the acrylonitrile copolymer is less than 70%, sufficient gas barrier properties cannot be obtained.

 The vinyl monomer copolymerizable with acrylonitrile is not particularly limited, but is a compound having a carbon-carbon unsaturated double bond, and includes (meth) acrylates, (Meth) acrylamides, (meth) acrylates having a functional group bonded thereto, vinylidenes, urethanes having an unsaturated bond, silicons having an unsaturated bond, fluorine-based unsaturated monomers Can use body. In particular, unsaturated carboxylic esters, specifically, methyl acrylate, ethyl acrylate, butyl acrylate, 2-ethylhexyl acrylate, and the like are preferable.

 The acryl-based copolymer is preferably prepared by emulsion polymerization of an acrylonitrile monomer and another vinyl-based monomer in the presence of a power emulsifier which can be produced by a known method. Examples of emulsifiers include fatty acid minerals, organic sulfonates, polyvinyl alcohol, methyl vinyl ether-maleic anhydride copolymers, and copolymers of olefin-maleic anhydride such as isobutylene-maleic anhydride, polyvinylpyrrole. And one or a mixture of two or more of these. .

 The type of polymerization initiator, surfactant, etc. is not particularly limited.However, since these substances remain in the coating film formed from the latex and cause deterioration of the gas barrier property, the amount of the substances used is limited. It is preferable that the amount is as small as possible.

In addition, the nitrile copolymer of [polymer] ¾ has poor melt fluidity, It is desirable to add a molecular weight regulator to reduce the molecular weight.

 The high nitrile copolymer thus obtained is used as a mixture with the polymer (A) and the polymer (B). The mixing ratio is within a range of 200 parts by mass or less with respect to the total 100 parts by mass of the polymer (A) and the polymer (B). If the amount of the high nitrile copolymer exceeds 200 parts by mass, the gas barrier properties decrease, and the film-forming properties deteriorate, so that a good coating film cannot be obtained.

 When the polymer (A) or the polymer (B) is mixed for the purpose of emulsifier or the like at the time of polymerization of the high nitrile latex, the amount of the coating agent is determined in consideration of these amounts.

 This coating agent includes heat stabilizers, antioxidants, reinforcing agents, pigments, deterioration inhibitors, weathering agents, flame retardants, plasticizers, release agents, lubricants, etc., as long as the properties are not significantly impaired. It may be added.

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

 (Coating agent adjustment)

 The coating agent can be adjusted by a known method using a dissolving pot equipped with a stirrer or the like. For example, polymer (A) and polymer

It is preferable to use (B) separately as an aqueous solution or an aqueous dispersion and to mix them before use. At this time, a small amount of an alcohol or an organic solvent can be added to water for the purpose of increasing the solubility, shortening the drying step, or improving the stability of the solution. Further, a compound serving as a catalyst for the reaction can be added. The thickness of the coat layer containing the polymer (A) and the polymer (B) is desirably at least greater than 0.1 m in order to sufficiently enhance the gas barrier properties of the film.

 The polymer concentration when the coating agent is coated on the film can be appropriately changed depending on the viscosity and reactivity of the liquid, the specifications of the equipment used, and the like. If the concentration is too low, it becomes difficult to coat a layer having a sufficient thickness necessary to exhibit gas barrier properties, and it is likely 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 and the storage stability. From such a viewpoint, the polymer concentration is preferably in the range of 1 to 50% by mass of the whole solution.

 The coating method of the coating agent on the film is not particularly limited, and ordinary methods such as gravure mouth coating, reverse roll coating, meyer bar coating, and die coating are used. be able to. The coating may be performed before stretching the film, or may be performed on the stretched film.

 At this time, the surface of the film is subjected to a corona discharge treatment prior to coating, or a polyester-based resin, an acrylic-based resin, A commonly known treatment such as coating a primer resin with a resin, a polyvinyl alcohol resin, a silyl group-containing resin, a melamine resin, or a mixture thereof may be applied.

When coating is performed prior to stretching, the unstretched film is coated and dried, and then supplied to a ten-stretch type stretching machine to stretch the film simultaneously in the Ji row direction and the width direction (simultaneously). 2 籼 Nobunaka) Heat treatment. After stretching in the running direction of the film using a multi-stage heat roll or the like, coating is performed, and after drying, the film may be stretched in the width direction by a ten-in-one stretching machine (sequentially) Biaxial stretching). It is also possible to combine the stretching in the running direction with the simultaneous stretching in _two directions. Coating prior to stretching, followed by stretching and heat treatment, is preferred because the high temperature during stretching and heat treatment can be used for the crosslinking reaction.

 The moisture content of the coat layer before stretching is preferably 0.1 to 50% by mass, more preferably 1 to 50% by mass, and particularly preferably 2 to 50% by mass. If the water content is less than 0.1% by mass, the coating layer is liable to peel or crack. On the other hand, if the water content exceeds 50% by mass, the drying efficiency of the coat layer is reduced and causes troubles such as film cutting during stretching.

 The moisture content of the coat layer before stretching varies depending on the solid content of the coating agent, the thickness of the coat layer, etc., but should be controlled to the desired range by changing the temperature and drying time of the dryer. Can be.

 The coat layer is a force formed on one or both sides of the film. In order to cause a cross-linking reaction between the polymer (A) and the polymer (B) in the coat layer, the temperature is 150 ° C. or higher, preferably 18 ° C. It is preferable to carry out heat treatment in an atmosphere of 0 or more.

 If the heat treatment temperature is low, the crosslinking reaction cannot proceed sufficiently, making it difficult to obtain a film having sufficient gas barrier properties.

Conversely, if the heat treatment temperature is too high, the performance and appearance of the film deteriorate due to thermal decomposition of the coat layer and the base film. Therefore, it is desirable that the heat treatment temperature be 230 ° C or less. (Electron beam)

 The coated film thus obtained exhibits excellent gas barrier properties by itself, and the gas barrier properties are improved particularly as the heat treatment time is increased. However, too long a heat treatment will reduce productivity.

 In the present invention, the gas barrier property can be further enhanced by irradiating the coated, dried, and heat-treated film with an electron beam. <The amount of the irradiated electron beam is 1 Mrad or more. 20 M rad or less is preferable, and l M rad or more and 15 M rad or less is more preferable. If the irradiation amount of the electron beam is less than 1 Mrad, sufficient cross-linking by irradiation with the electron beam cannot be introduced, and the improvement of the gas nori- bility based on the irradiation of the electron beam becomes insufficient. Conversely, if the irradiation dose is more than 20 Mrad, the gas barrier properties will decrease. This is thought to be due to adverse effects such as breakage of molecular chains due to excessive irradiation. It is not clear why the gas barrier property is improved by irradiating the film with an electron beam.The main components of the coating layer, PVA and the copolymer of maleic and maleic acid, have a very high affinity. PVA is hardly crystallized because the domain of each component is very small, even if it is not completely mixed or not.Therefore, there is little restriction of molecular chains, and a crosslinked structure is easily formed by electron beams. It is thought to be. Example

 Hereinafter, examples of the present invention will be described. In addition, various physical property values were obtained as follows.

Oxygen permeability The oxygen permeability in an atmosphere at 20 ° C and a relative humidity of 85% was measured using a Mocon oxygen barrier measuring instrument.

Oxygen permeability coefficient of coating layer

 The gas barrier properties of the film vary depending on the type and thickness of the base film and the thickness of the coating layer. Therefore, the oxygen permeability coefficient of the coating layer itself was evaluated.

 This oxygen permeability coefficient was determined by the following equation.

1 / QF 2 1 ZQ _b + L / PC

Where Q _F : oxygen permeability of the coat film (ml Zm ² / day ZM Pa)

QB: oxygen permeability of the thermoplastic resin film ^{(ml / m 2 / day /} MP a)

P c: Oxygen permeability coefficient of the coating layer (ml-m / m ² Z day ZM P a)

 L: Coating layer thickness (m)

 Therefore, the oxygen permeability of the coated film can be estimated from the above equation if P c and L are known.

The oxygen permeability of the film used in the following examples at 20 ° C. and 85% RH was as follows. This film was a biaxially stretched PET film (900 ml / m ² Z day / MP a, if the film strength biaxially stretched nylon film (thickness 1 is ^{4 0 0 ml Zm 2 / day} ZM P a. Therefore, this value is the calculation of the oxygen permeability coefficient of the coat layer Was used.

□ Moisture percentage of single layer

The moisture content of the coat is determined after coating the film with the coating agent. Is dried, and the coat film of Nobenaka is collected. The total mass of the coat layer is a gram, and the mass of water in the coat layer is b gram. (B / a) XI 00 (mass% ). The mass of water in the coat layer was determined by subtracting the mass after completely drying the coat layer from the total mass of the coat layer.

Appearance of coat film

 The appearance of the coated film was visually evaluated. When no peeling or cracking of the coat layer was observed, the evaluation was “good”. Conversely, if peeling or cracking of the coat layer was observed, it was evaluated as “poor”.

(Example 1)

 As the polymer (A), a polyvinyl alcohol UF040G (99% saponification degree, average polymerization degree 500) manufactured by Unitika Chemical Co., Ltd. was dissolved in pure water to obtain a 10% by mass aqueous solution. On the other hand, polymer

As (B), a methyl vinyl ether-maleic acid equimolar copolymer GAN TREZ AN119 manufactured by International Specialty Products, Inc. was converted to 5 mol% of hydroxylated hydroxyl group based on the carboxyl group of G AN TREZ. It was dissolved in an aqueous solution containing lithium to obtain a 10% by mass solution. Next, the two aqueous solutions are mixed so that the mass ratio of the polymer (A) and the polymer (B) becomes (A) / (B) = 74/26, and the mixture is stirred at room temperature to obtain a liquid coating agent. Was prepared.

This coating agent was coated on a biaxially stretched PET film (thickness: 12 m) with a Meyer bar coat so that the coating thickness after drying was about 2 m, and dried at 100 ° C for 2 minutes. Thereafter, heat treatment was performed at 200 ° C. for 5 minutes. The resulting film has an excellent oxygen permeability of 40 m ^1/2 / day / MP, and the estimated oxygen permeability coefficient of the coating layer is 84 ml-m / m ² Z day ZM Pa.

 (Comparative Example 1)

The same operation as in Example 1 was performed using only the PVA aqueous solution as the coating agent. The resulting film has an oxygen permeability of 410 m 1 / m ² / day / MPa, which is insufficient for gas packaging for food packaging films. The oxygen permeation coefficient was 1657 ml · m / ² Z day ZMPa.

 (Examples 2 to 7, Comparative Examples 2 and 3)

 The same operation as in Example 1 was performed by changing the types and ratios of the polymer (A) and the polymer (B), and the oxygen permeability of the obtained film and the oxygen permeability coefficient of the coat layer were determined. The results are shown in Table 1. Here, Isoban is an isobutylene-maleic anhydride copolymer manufactured by Kuraray Co., Ltd., SMA1000 and SMA2000 are styrene-monomaleic anhydride copolymers manufactured by Atochem, and E MA is an ethylene-maleic anhydride copolymer manufactured by ALDRICH.

From the results shown in Table 1, the film of the present invention is useful because it has excellent gas barrier properties, and its coating agent has much better performance than PVA, which is generally used as a gas barrier coating agent. It turns out that it is. table 1

 Film: PET12 / i m

 Heat treatment: 200 ° C, 5 minutes

 Vinyla Vinylalmalein Maleic acid (A) Alkalinized (B) Alkali compound Coat Oxygen permeability Acid in the coat layer Coal unit Acid unit content Unit content Mass fraction Mass fraction Compound addition amount Thickness Permeability coefficient Poly content Poly content

 Ma mar

 (A) (mol%) (B) (mol%) Parts by mass Parts / mVd / Pa (mol%) based on carnetoxy IX in ml B / ml / m / d / MPa ml · m

Example 1 UF040G 99 Gantrez 50 74 26 NaOH 5 2 40 84 Example 2 UF040G 99 Gantrez 50 24 76 NaOH 5 2 120 277 Example 3 UF040G 99 SMA1000 50 47 53 NaOH 5 2 140 332 Example 4 UF040G 99 S A2000 50 37 63 NaOH 20 1.9 190 458 Example 5 EVOH 73 Gantrez 50 47 53 NaOH 5 2.1 110 263 Example 6 UF040G 99 iso ', ン 04 50 55 45 NaOH 50 2 90 200 Example 7 UF040G 99 EMA 50 60 40 NaOH 5 2 55 117 Comparative Example 1 UF040G 99 100 0 2.2 410 1657 Comparative Example 2 UF040G 99 Gantrez 50 7 93 NaOH 5 2.1 630 4410 Comparative Example 3 UF040G 99 SMA1000 50 7 93 NaOH 5 2 850 30600

(Examples 8 to 12, Comparative Example 4)

 The same operation as in Example 1 was performed by changing the type and amount of the alkali, and the coating agent was adjusted. The obtained coating agent was coated on a PET film in the same manner as in Example 1, dried at 100 ° C. for 2 minutes, and then heat-treated for different times. Table 2 shows the oxygen permeability of the obtained film and the oxygen permeability coefficient of the coating layer.

 (Example 13)

 As the polymer (A), the above-mentioned UF040G was dissolved in pure water to obtain a 20% by mass aqueous solution. As a polymer (B), the above-mentioned GANTREZAN 119 was dissolved in an aqueous solution containing 5 mol% of sodium hydroxide with respect to the carboxylic acid unit to obtain a 20% by mass solution.

 Next, both aqueous solutions were mixed so that the mass ratio of the polymer (A) and the polymer (B) became (A) / (B) 70Z30, to prepare a coating agent.

 Next, using an extruder equipped with a T die (slow compression type single screw screw with a diameter of 75 mm and an LZD of 45), the temperature of the thin cylinder was 260 ° C, and the temperature of the T die was 2 ° C. At 80 ° C, the PET resin was extruded in a sheet form, closely adhered to a cooling roll adjusted to a surface temperature of 10 ° C, and rapidly cooled to obtain an unstretched film having a thickness of 120m. Subsequently, the unstretched film is guided through a gravure roll type coater, coated with a coating agent so that the coat thickness after drying becomes 20 m, and heated in a hot air dryer at 80 ° C. Dried for 30 seconds. Next, this film is fed to a ten-set simultaneous biaxial stretching machine, preheated at 100 ° C for 2 seconds, and then tripled in the vertical direction and 3.5 times in the horizontal direction at 95 ° C. The film was stretched at twice the magnification.

15 seconds at 200 ° C with 5% relaxation in the 橫 direction The film was rolled up after a heat treatment for a period of time and cooling to room temperature. Table 2 shows the oxygen permeability of the obtained film and the oxygen permeability coefficient of the coating layer.

 (Example 14)

 Using the same extruder as used in Example 13, Nylon 6 resin was extruded in a sheet shape at a temperature of 260 ° C. for the thin cylinder and 270 ° C. for the T-die, The film was quenched by closely contacting it on a cooling roll adjusted to a surface temperature of 10 ° C. to obtain an unstretched film having a thickness of 150 Aim. Subsequently, the unstretched film was led to a gravure roll type coater overnight, and the same liquid as used in Example 13 was coated and dried under the same conditions. Next, a film was produced under the same conditions as in Example 13 except that the temperature condition during stretching was set to 170 ° C.

 Table 2 shows the oxygen permeability of the obtained film and the oxygen permeability coefficient of the coating layer.

From the results in Table 2, it can be seen that by appropriately adjusting the degree of neutralization and pH of the coating agent, a film having excellent gas barrier properties can be obtained even with a relatively short heat treatment.

Table 2

 (A) Polyvinyl alcohol: UF040G

 (B) Maleic anhydride polymer: Gantrez ΑΝΠ9

 Base film Film thickness (A) 1 (B) Alkali compound Alkali compound pH heat treatment temperature heat treatment Coat Oxygen permeability Acid in coat layer

 Addition halo time) 1

m Cal ratio in mass ratio B '° C sec β m ml / m ² / d / Pa ml

/ M ² / d / Pa

 Then (mo

 0?)

Example 8 PET 12 60/40 NaOH 5 3.0 200 60 2.0 45 95

Example 9 PET 12 80/20 NaOH 1 2.8 200 60 1.9 55 111

Example 10 0 PET 12 90/10 NaOH 2 3.5 200 60 1.8 73 143

Example 1 1 PET 12 70/30 Ca (OH) 2 5 3.0 200 15 2.0 95 212

Example 1 2 PET 12 70/30 NH ₃ 15 3.7 200 15 2.1 170 440

Example 1 3 PET 12 70/30 NaOH 5 2.9 200 15 2.0 75 164

Example 14 Nylon 15 70/30 NaOH 5 2.9 200 15 2.0 65 155 00 Comparative Example 4 PET 12 80/20 NaOH 1 2.8 150 60 2.0 530 2578 ^

(Example 15)

 As the polymer (A), the above-mentioned UF040G was dissolved in pure water to obtain a 10% by mass aqueous solution. As a polymer (B), the above-mentioned GANTREZAN 119 was dissolved in an aqueous solution containing 2 mol% of sodium hydroxide with respect to the carboxyl group to obtain a 10% by mass solution. '

 Then, both aqueous solutions were mixed such that the mass ratio of the polymer (A) and the polymer (B) was (A) / (B) = 80Z20. Subsequently, an isocyanate compound dispersion (Elastron BN11) manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd. was mixed with a polymer having a mass ratio of the isocyanate compound of 100 (solid) of polymer (A) and polymer (B). It was added so as to be 5 parts by mass with respect to parts by mass, and stirred to prepare a coating agent.

This coating agent was coated on a biaxially stretched PET film (thickness: 12 xm) using a Meyer bar so that the coating thickness after drying was about 2 m, and dried at 100 ° C for 2 minutes. Thereafter, heat treatment was performed 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 m 1 / ^z / day / MPa as shown in Table 3.

 (Examples 16 to 22 and Comparative Example 5)

 The same operation as in Example 15 was performed by changing the types and ratios of the polymer (A) and the polymer (B), and the type and amount of the crosslinking agent, respectively, to thereby obtain an oxygen permeability and a coat of the obtained film. The oxygen permeability coefficient of the layer was determined. The results are shown in Table 3.

 (Examples 23 to 25)

来 The same stretched nylon film as that of Example 14 was led to a gravure roll type co-polymer overnight, and the composition was as shown in Table 3 and the crosslinking agent was as shown in Table 3. A film was produced under the same conditions as in Example 14 using a coating agent to which was added.

Table 3 shows the oxygen permeability of the obtained film and the oxygen permeability coefficient of the coating layer.

Table 3

 Isocyanate (I): Daiichi Kogyo Seiyaku Co., Ltd .: I Laston BN11 Isocyane h (II): Daiichi Kogyo Seiyaku Co., Ltd .: I Last Q E-37 Melamine: Mitsui Cytec: Cyme 1325

I-honki: Made by Tokyo Kasei Co., Ltd .: Fushi-tanshi-shi-Rusi-Gerishishi-ru I-Terkar-ki-shi: Imide: Nisshinbo Co., Ltd .: Calho-shi 'Ra-E-shi' ruconium salt First rare element '; / Luco' / -Lu AC-7

(Example 26)

 As the polymer (A), the above UFO40G was dissolved in pure water to obtain a 20% by mass aqueous solution. As a polymer (B), the above-described GANTEZAN 119 was dissolved in an aqueous solution containing 2 mol% of sodium hydroxide with respect to the carboxyl group to obtain a 20% by mass solution.

 Next, both aqueous solutions were mixed such that the mass ratio of the polymer (A) and the polymer (B) became (A) Z (B) = 70Z30. Subsequently, Kunipia F, a montmorillonite manufactured by Rinmine Industrial Co., was used as an inorganic layered compound, and the mass ratio thereof was 1 to the total solid parts by mass of the polymer (A) and the polymer (B). It was added so as to be 0 parts by mass and stirred to prepare a coating agent.

This coating agent was coated on a biaxially stretched PET filem (thickness: 12 zm) using a Meyer bar so that the coating thickness after drying was about 2 m, and dried at 100 ° C for 2 minutes. Thereafter, heat treatment was performed at 200 ° C. for 15 seconds. The oxygen permeability of the obtained film at 20 and 85% RH showed an excellent value of 26 m 1 / m ² / day / MPa as shown in Table 4.

 (Examples 27 to 32)

 The same operation as in Example 26 was performed after changing the kind and amount of the inorganic layered compound, the composition of the coating agent, and the base film. The results are shown in Table 4. In Table 4, Somasif is a swellable synthetic fluoromica manufactured by Corp Chemical.

 (Example 33)

The same unstretched nylon film as that of Example 14 was led to the gravure roll type co-polymer overnight, and the same coating agent as that used in Example 26 was used. Was coated so that the coat thickness after drying was 11 m, and a film was produced under the same conditions as in Example 14.

 Table 4 shows the oxygen permeability of the obtained film and the oxygen permeability coefficient of the coat layer.

 (Example 34)

 As the polymer (A), the above-mentioned UF • 40G was dissolved in pure water to obtain a 10% by mass aqueous solution. As a polymer (B), the above-mentioned isoban 04 was dissolved in an aqueous solution containing 60 mol% of ammonium hydroxide with respect to the carboxyl group to obtain a 10% by mass solution. Then, both aqueous solutions were mixed so that the mass ratio of the polymer (A) and the polymer (B) became (A) Z (B) = 70Z30 to obtain a coating agent. The same operation as in Example 33 was performed using this coating agent.

Table 4 shows the oxygen permeability of the obtained film and the oxygen permeability coefficient of the coat layer.

Table 4

 Coat thickness 2 zm

o

(Example 35)

 As the polymer (A), the above UFO40G was dissolved in pure water to obtain a 10% by mass aqueous solution. As a polymer (B), the above-mentioned GANTREZAN 119 was dissolved in an aqueous solution containing 2 mol% of sodium hydroxide with respect to the carboxyl group to obtain a 10% by mass solution.

 Next, both aqueous solutions were mixed so that the mass ratio of the polymer (A) and the polymer (B) would be (A) / (B) = 71 Z29, and the Nippon Xlan Co., Ltd. The lonitrile copolymer emulsion (97% by mass of acrylonitrile) was added in an amount of 43 parts by mass based on 100 parts by mass of the solid content of the polymer (A) and the polymer (B). Parts, and stirred to prepare a coating agent.

 This coating agent was coated on a biaxially stretched PET film (thickness: 12 m) using a Meyer bar so that the coating thickness after drying was about 2 m, and dried at 100 ° C for 2 minutes. Thereafter, heat treatment was performed at 200 for 10 seconds. Table 5 shows the performance of the obtained gas barrier film.

 (Example 36, Comparative Example 67)

220 parts of water and 0.04 parts of persulfuric acid soda were charged into a pressure-resistant reactor lined with glass, and after degassing, the temperature of the contents was kept at 80 ° C. In a separate container, 80 parts of acrylonitrile, 18 parts of methyl acrylate, and 2 parts of methyl methacrylate were weighed and mixed to prepare a monomer mixture. The monomer mixture was continuously metered into the pressure-resistant reactor over 5 hours. At the same time, 0.6 parts of sodium persulfate (added as a 1.48% aqueous solution) and sulfometrichlorate (H-Emulsifier: brand name Anto XMS-2N) 2 parts (but added as a 4.76% aqueous solution) over 5 hours It was continuously added quantitatively. During this time, the content was maintained at 80 ° C, and the reaction was allowed to proceed until the internal pressure was sufficiently reduced.

 This was mixed with an aqueous solution of the polymer (A) and the polymer (B) prepared in the same manner as in Example 35, and the total solid content of (A) and (B) was 100 parts by mass. The coating agent was adjusted so that the amount of the tril copolymer was as shown in Table 5.

 This coating agent was coated on a biaxially stretched PET film (Emblend PET 12 manufactured by Unitika Ltd., thickness 12 m) with a Meyer bar so that the coating thickness after drying was about 2 m. After drying at 00 ° C for 2 minutes, heat treatment was performed at 200 ° C for 10 seconds. Table 5 shows the results.

In Comparative Example 6, in which the content of the acrylonitrile copolymer was larger than the range of the present invention, no good coating film was obtained. In Comparative Example 7 using a copolymer having a low acrylonitrile ratio, the gas barrier property was poor.

Table 5

 Coat thickness 2 Attn

 Neutralization Gantrez: 2% (NaOH). Iso /, ': 60¾ (Paint, SMA: 5¾ (NaOH) Heat treatment 200 ° (:, 10 seconds

 Base film Film thickness Vinyla Vinylalmalein Maleic acid (A) 1 (B) Acrylo: triΛ7. Nitrile Coat Coat fill Oxygen permeable Coal layer alcohol Coal unit Acid unit content Unit content Content Copolymer agent concentration Viscosity viscosity Appearance Oxygen permeation content Poly content Poly content

 Ma mar

m (A) (mol%) (B) (mol%) Mass ratio mass% mass parts mPas ml / m ² / d ml ·

 / MPa / m2 / d / MPa Example 35 PET 12 UF040G 99 Gantrez 50 71/29 97 43 10 200 Good 110 251

Example 36 PET 12 UF040G 99 Gantrez 50 80/20 80 100 10 160 Good 140 332

Comparative example 6 PET 12 UF040G 99 Gantrez 50 80/20 80 900 10 30 defective 900

Comparative Example 7 PET 12 UF040G 99 Gantrez 50 80/20 60 100 10 140 Good 680 5564

O CO

(Examples 37 and 38)

 The above-mentioned UF040G as the polymer (A) was dissolved in pure water to obtain a 10% by mass aqueous solution. As a polymer (B), the above-mentioned GANTREZAN 119 was dissolved in an aqueous solution containing 5 mol% of sodium hydroxide with respect to the carboxyl group to obtain a 10% by mass solution.

 Next, both aqueous solutions were mixed such that the mass ratio of the polymer (A) and the polymer (B) became (A) / (B) = 70/30, and the mixture was stirred at room temperature to prepare a coating agent.

 This coating agent was coated on a biaxially stretched PET film (thickness: 12 m) using a Meyer bar so that the coating thickness after drying was about 2 m, and dried at 100 for 2 minutes. Heat treatment was performed at 200 ° C. for 10 seconds. Thereafter, the film was introduced into an electron beam irradiation apparatus (Curetron, manufactured by Nissin High Voltage), and the film was irradiated with an electron beam at an accelerating voltage of 175 kV and at a dose shown in Table 6.

 Table 6 shows the results.

In Examples 37 and 38, the oxygen permeability of the film before irradiation with an electron beam was 150 ml Zm ² Z day. (Comparative Example 8)

 The same operation as in Examples 37 and 38 was performed using a liquid containing only the polymer (A) as the coating agent. Table 6 shows the results.

Table 6 shows that the gas barrier property can be further improved by irradiating the coated film with an electron beam according to the present invention. In Comparative Example 8, that is, when only PVA was coated, no improvement in gas barrier properties was observed even when electron beams were irradiated. Table 6

 Thickness 2

(Examples 39 and 40, Comparative Examples 9 and 10)

 The same coating agent as that of Example 37 was prepared, and the same non-rolled nylon film as that of Example 14 was obtained.

 Subsequently, the unstretched film was guided to a gravure roll type coater overnight, and the coating agent prepared above was coated so that the coat thickness after drying became 20 m, and the temperature was adjusted to 80 ° C. Drying was performed in a hot air drier so that the moisture content of the coat layer became the value shown in Table 7.

 Next, a film was produced under the same conditions as in Example 14.

 Table 7 shows the oxygen permeability of the obtained film and the oxygen permeability coefficient of the coat layer.

As is clear from Table 7, in Examples 39 and 40 in which the moisture content of the coat layer was within the range of the present invention, the film stretchability and the appearance of the coat layer were also good. On the other hand, in Comparative Example 9 in which the coat layer was completely dried, cracks occurred in the coat layer, and a good film could not be obtained. In the case of Comparative Example 10 in which the moisture content of the coat layer was as high as 200%, the temperature of the base film was not increased in the stretching step, and the film could not be stretched.

Coating composition: PVA / Gantrez (5% neutralized) = 70/30

Claims

The scope of the claims

 1. A gas barrier film comprising a vinyl polymer (A) containing at least 40 mol% of vinyl alcohol units and a vinyl polymer (B) containing at least 10 mol% of maleic acid units. The coated δ layer is provided on at least one side of the thermoplastic resin film.

The mass ratio to (Β) is 97 Ζ 3 to 20/80, and the oxygen permeability coefficient of the coating layer is 500 ml-^ mm ² Z day ZM Pa or less. .

 2. The gas barrier film according to claim 1, wherein the vinyl polymer (A) is polyvinyl alcohol.

 3. The gas barrier film according to claim 1, wherein the vinyl polymer (B) power, methyl vinyl ether / maleic anhydride copolymer, ethylene / maleic anhydride copolymer, and isobutylene One of a maleic anhydride copolymer and a mixture thereof.

 4. The gas barrier film according to any one of claims 1 to 3, wherein a total of 100 parts by mass of the vinyl polymer (A) and the vinyl polymer (B) is crosslinked. The agent is contained in the range of 0.1 to 20 parts by mass.

 0 5. The gas barrier film according to claim 4, wherein the crosslinking agent is a melamine compound or an isocyanate compound.

6. The gas-free film according to any one of claims 1 to 5, wherein the total amount of the vinyl polymer (A) and the vinyl polymer (B) is 100 parts by mass. It contains water-swellable inorganic compounds in the range H of 0.15 to 50 5li.

7. The gas barrier film according to claim 6, wherein the water-swellable inorganic layered compound is fluorine mica.

 8. The gas according to any one of claims 1 to 7, which is a lyophilizable film, wherein the total amount of the vinyl polymer (A) and the vinyl polymer (B) is 100 parts by mass. Containing an acrylic copolymer containing at least 70 mass% of acrylonitrile units in a range of 200 mass% or less,

9. The gas barrier film according to any one of claims 1 to 8, wherein the oxygen permeability coefficient of the coating layer is 250 ml-m / m ² / day ZM Pa or less. is there.

 10. The gas barrier film according to any one of claims 1 to 9, wherein the thermoplastic resin is nylon 6.

1 1. The gas barrier film according to claim 10, wherein the oxygen permeability is not more than 180 mm md ay / M Pa (converted to a nylon film of 15 m).

 1 2. The gas barrier film according to any one of claims 1 to 9, wherein the thermoplastic resin is polyethylene terephthalate.

1 3. The gas barrier film according to claim 12, wherein the oxygen permeability is not more than 250 ml Zm ² / day / MPa (polyethylene terephthalate film 12 equivalent).

 1 4. A method for producing a gas barrier film according to any one of claims 1 to 13, wherein the method comprises applying a coating agent on at least one side of the film. The heat treatment is performed at a temperature of 0 ° C or more.

15. The manufacturing method according to claim 14, wherein after applying the coating agent to the film, the film is applied in at least one of the longitudinal direction and the lateral direction of the film. The film is stretched and then heat treated.

 1 6. The manufacturing method according to claim 15, wherein the two processes are performed simultaneously.

17. The production method according to claim 15 or 16, wherein when the coating layer is applied after the coating layer is applied, the water content of the coating layer immediately before stretching is 0.1 to 50. % By mass.

 1 8. The manufacturing method according to any one of claims 14 to 17, wherein the heat-treated film is irradiated with an electron beam.

 1 9. The process according to any one of claims 14 to 18, wherein the vinyl polymer (B) f) forming the coating agent is methyl vinyl ether monomaleic anhydride copolymer. The vinyl polymer (B) contains 0.1 to 20% equivalent of the alkali compound with respect to the carboxyl group in the vinyl polymer (B).

 20. The method according to any one of claims 14 to 18, wherein the pH of the coating agent is in the range of 2.8 to 3.7.