JP2004136281A - Method of producing gas barrier laminate - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To produce a film and its laminate excellent in oxygen gas barrier property under a high humidity and free from chlorine in the structure under a more moderate condition than that of the conventional method. <P>SOLUTION: The method of producing a gas barrier laminate is such that a plastic substrate directly or through an under coat layer is coated with a coating (C) for forming the gas barrier layer containing polyvinyl alcohol (A) and an ethylene maleic acid copolymer (B) and that after heat treatment the above coated substrate is heated in the presence of water. <P>COPYRIGHT: (C)2004,JPO

Description

The present invention relates to a method for producing a gas barrier laminate having excellent gas barrier properties even under high humidity.

Thermoplastic resin films such as polyamide films and polyester films are used in a wide range of applications as packaging materials because of their excellent strength, transparency and moldability. However, since these thermoplastic resin films have high gas permeability such as oxygen, when used for packaging of general foods, retorted foods, cosmetics, medical supplies, pesticides, etc., the films permeated the films during long-term storage. The contents such as oxygen may be altered by the gas.

Therefore, a laminated film in which an emulsion of polyvinylidene chloride (hereinafter abbreviated as PVDC) or the like is coated on the surface of a thermoplastic resin to form a PVDC layer having a high gas barrier property has been widely used for food packaging and the like. However, since PVDC generates organic substances such as acid gas at the time of incineration, interest in the environment has increased in recent years, and there has been a strong demand for transfer to other materials.

Polyvinyl alcohol (hereinafter abbreviated as PVA) as a material that substitutes for PVDC does not generate toxic gas and has high gas barrier properties in a low-humidity atmosphere. In many cases, it cannot be used for packaging of foods and the like.

A copolymer of vinyl alcohol and ethylene (EVOH) is known as a polymer that has improved the gas barrier property of PVA under high humidity. However, in order to maintain the gas barrier property at a high humidity at a practical level, it is necessary to increase the copolymerization ratio of ethylene to some extent, and such a polymer becomes sparingly soluble in water.
Therefore, in order to obtain a coating agent using EVOH having a high ethylene copolymerization ratio, it is necessary to use an organic solvent or a mixed solvent of water and an organic solvent. Since a process is required, there is a problem that the cost is increased.

As a method of coating a liquid composition composed of a water-soluble polymer on a film and expressing high gas barrier properties even under high humidity, an aqueous solution composed of PVA and a partially neutralized product of polyacrylic acid or polymethacrylic acid is coated on the film. Then, a method of crosslinking both polymers by an ester bond by heat treatment is proposed (Patent Document 1: JP-A-06-220221, Patent Document 2: JP-A-07-102083, Patent Document 3: JP-A-07-2007). -205379, Patent Document 4: 07-266441, Patent Document 5: 08-041218, Patent Document 6: 10-237180, Patent Document 7: JP-A-2000-000931 Etc.).
However, in the method proposed in the above publication, a high-temperature heat treatment or a long-time heat treatment is required in order to exhibit a high gas barrier property, and a large amount of energy is required during production, so that the load on the environment is reduced. Not a few.
In addition, when heat treatment is performed at a high temperature, there is a risk of discoloration or decomposition of the PVA or the like forming the barrier layer, and deformation of the base material such as a plastic film on which the barrier layer is laminated, such as wrinkles, is generated. Can no longer be used. In order to prevent the deterioration of the plastic base material, it is necessary to use a special heat-resistant film capable of sufficiently withstanding high-temperature heating as a base material, which is difficult in terms of versatility and economy.
On the other hand, when the heat treatment temperature is low, it is necessary to perform the treatment for a very long time, and there is a problem that productivity is reduced.

Also, studies have been made to solve the problems of the PVA film by introducing a crosslinked structure into PVA. However, in general, the humidity dependency of the oxygen gas barrier property of the PVA film becomes smaller as the crosslink density increases, but the oxygen gas barrier property under the drying conditions that the PVA film originally has decreases, and as a result, It is very difficult to obtain good oxygen gas barrier properties under high humidity.
In general, cross-linking of polymer molecules improves water resistance, but gas barrier property is a property of preventing intrusion and diffusion of relatively small molecules such as oxygen. However, three-dimensionally crosslinkable polymers such as epoxy resins and phenolic resins do not have gas barrier properties.

A method has been proposed in which a gas barrier laminate having a high gas barrier property even under high humidity using a water-soluble polymer such as PVA is provided by heat treatment at a lower temperature or for a shorter time than before (Patent Document 8). JP-A-2001-323204, Patent Document 9: JP-A-2002-020677, and Patent Document 10: JP-A-2002-241671).

The coating agents described in Patent Literatures 8 to 10 have a higher gas barrier than conventional coating materials at a lower temperature or a shorter heating time and higher humidity than the coating agents described in Patent Literatures 1 to 7, even though a water-soluble polymer is used. A gas barrier laminate having properties can be formed.
However, according to Patent Documents 1 to 10, by heating, the hydroxyl group in PVA is subjected to an esterification reaction with COOH in polyacrylic acid or in ethylene-maleic acid copolymer, or a metal crosslinked structure is introduced. According to the method, there is a limit in improving the gas barrier property under high humidity. That is, even when the heating conditions are higher and longer, the oxygen permeability does not decrease beyond a certain value, but rather increases, the reverse phenomenon occurs. This is probably because the plastic substrate and the barrier layer being formed were thermally deteriorated by the severe heating conditions. Heating conditions of high temperature and long time also cause coloring and curling of the plastic substrate and the barrier layer being formed, which is not preferable in this respect.
As a result of the above, today, where further improvement in gas barrier properties under high humidity is increasingly demanded, merely heating and curing the coating agents described in Patent Documents 1 to 10 did not meet the more stringent requirements.
JP-A-06-220221 JP-A-07-102083 JP 07-205379 A JP-A-07-266441 JP 08-041218 A JP-A-10-237180 JP 2000-000931 A JP 2001-323204 A JP-A-2002-020677 JP-A-2002-241671

課題 The object of the present invention is to provide a gas barrier laminate having a higher gas barrier property under high humidity than before using a water-soluble polymer under milder conditions than before.

The present inventors have assiduously studied and as a result, surprisingly, it is possible to dramatically improve the barrier property by using water, which has been considered to be a major cause of the lowering of the barrier property. Heading reached the present invention.
That is, the first invention provides a gas barrier containing polyvinyl alcohol (A) and an ethylene-maleic acid copolymer (B) directly on a plastic substrate or on a plastic substrate via an undercoat layer. The present invention relates to a method for producing a gas-barrier laminate, which comprises applying a layer-forming coating material (C), performing a heat treatment, and then performing a heat treatment in the presence of water.

The second invention relates to the method for producing a gas barrier laminate according to the first invention, wherein the paint (C) contains a divalent or higher valent metal compound.
A third invention relates to the method for producing a gas barrier laminate according to the second invention, wherein the divalent or higher valent metal compound can react with a hydroxyl group or a carboxyl group,
A fourth invention relates to the method for producing a gas barrier laminate according to the second or third invention, wherein the divalent or higher-valent metal is Mg.
A fifth invention is described in the fourth invention, wherein the Mg compound is contained in an equivalent amount of 0.05 to 12.5% with respect to the carboxyl group in the ethylene-maleic acid copolymer (B). The present invention also relates to a method for producing a gas barrier laminate of the present invention.

A sixth invention is directed to any one of the first to fifth inventions, wherein the weight ratio between the polyvinyl alcohol (A) and the ethylene-maleic acid copolymer (B) is 90/10 to 10/90. The present invention also relates to a method for producing a gas barrier laminate according to the above.

A seventh invention is the gas barrier laminate according to any one of the first to sixth inventions, wherein the undercoat layer is formed from a polyester polyol having a glass transition temperature of 0 ° C. or higher and a polyisocyanate. And a method for producing the same.

８ An eighth invention relates to the method for producing a gas barrier laminate according to any one of the first to seventh inventions, wherein the method is heat-treated at 90 ° C. or higher in the presence of water.

According to the present invention, it is possible to provide a method for producing a gas barrier laminate having no chlorine in the structure, excellent in oxygen gas barrier properties under high humidity, and having a significantly higher gas barrier property than conventional ones. .

Hereinafter, the present invention will be described in detail.
[Paint for forming gas barrier layer (C)]
The coating material (C) for forming a gas barrier layer is applied to a plastic substrate or the like described below to impart gas barrier properties, and is composed of PVA (A) and an ethylene-maleic acid copolymer (hereinafter, referred to as EMA) ( B).

<PVA (A)>
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. Of these, vinyl acetate is the most industrially preferred.

で Other vinyl compounds can be copolymerized with the vinyl ester as long as the effects of the present invention are not impaired. Other vinyl monomers include unsaturated monocarboxylic acids such as crotonic acid, acrylic acid, and methacrylic acid, and esters, salts, anhydrides, amides, and nitriles thereof, and unsaturated acids such as maleic acid, itaconic acid, and fumaric acid. Examples thereof include dicarboxylic acids and salts thereof, α-olefins having 2 to 30 carbon atoms, alkyl vinyl ethers, and vinylpyrrolidones.

In the present invention, the polymer laminated to impart gas barrier properties to the film surface is preferably water-soluble for production, and if a large amount of a hydrophobic copolymer component is contained, the water-solubility is impaired, which is not preferable.

As the saponification method, a known alkali saponification method or acid saponification method can be used, and among these, a method of alcoholysis using methanol in an alkali hydroxide is preferable. The degree of saponification is preferably as close to 100% from the viewpoint of gas barrier properties. If the degree of saponification is too low, the barrier performance decreases. Usually, the degree of saponification is preferably about 95% or more, and more preferably 98% or more. The average degree of polymerization is preferably from 50 to 4,000, more preferably from 200 to 3,000.

<EMA (B)>
The ethylene-maleic acid copolymer (B) used in the present invention is obtained by polymerizing maleic anhydride and ethylene by a known method such as solution radical polymerization. It is also possible to copolymerize a small amount of another vinyl compound within a range that does not impair the object of the present invention. Examples of the vinyl compound include acrylates such as methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, butyl acrylate, and butyl methacrylate; vinyl formate; vinyl esters such as vinyl acetate; Examples thereof include olefins having 3 to 30 carbon atoms such as styrene, p-styrenesulfonic acid, propylene, and isobutylene, and compounds having a reactive group that reacts with a hydroxyl group of PVA.

The maleic acid unit in the EMA (B) in the present invention preferably contains at least 10 mol%, and an alternating copolymer of ethylene and maleic anhydride having approximately equimolar maleic acid units is preferable. When the amount of the maleic acid unit is less than 10 mol%, the formation of a crosslinked structure by the reaction with the PVA unit is insufficient, and the gas barrier property is reduced.
The EMA (B) used in the present invention preferably has a weight average molecular weight of 3,000 to 1,000,000, more preferably 5,000 to 900,000, and still more preferably 10,000 to 800,000.

In the EMA (B) used in the present invention, the maleic acid unit easily becomes a maleic anhydride structure in which adjacent carboxyl groups are dehydrated and cyclized in a dry state. Structure.

In the coating material (C) for forming a gas barrier layer used in the present invention, the weight ratio of PVA (A) to EMA (B) is preferably (A) / (B) = 90/10 to 10/90, and 70 / 30 to 15/85, more preferably 60/40 / to 20/80, and particularly preferably 50/50 to 25/75. If either PVA (A) or EMA (B) is relatively large, the effect of improving the barrier properties is small even if heat treatment is performed in the presence of water.

ガ ス The gas barrier layer forming paint (C) used in the present invention preferably contains a divalent or higher valent metal compound (D) in addition to PVA (A) and EMA (B). By containing the divalent or higher valent metal compound (D), a crosslinked structure can be formed in the barrier layer. It is preferable that the divalent or higher valent metal compound (D) can react with a hydroxyl group or a carboxyl group. A crosslinked structure is suitably formed by reacting with a hydroxyl group or a carboxyl group. The cross-linking structure generated here may be a coordination bond as well as an ionic bond or a covalent bond.

Examples of the metal compound (D) capable of reacting with a hydroxyl group or a carboxyl group include:
Halides, hydroxides, oxides, carbonates, phosphates, phosphites, hypophosphites, sulfates or sulfites (D1) of divalent or higher valent metals,
Zirconium complex salts, zirconium halides, zirconium salts of inorganic acids or zirconium salts of organic acids (D2) and the like are preferred, and the metal compound (D1) is preferred. As the divalent or higher valent metal compound (D), one kind selected from each group may be used alone, two or more kinds in each group may be used in combination, or one selected from each group may be used. More than one species can be used in combination.

As the metal compound (D1), hydroxides, oxides, carbonates, phosphates, phosphites, hypophosphites, and sulfates of divalent or higher-valent metals are preferable.
As the divalent or higher valent metal, Mg, Ca, Zn, Cu, Co, Fe, Ni, Al or Zr are preferable, Mg and Ca are more preferable, and Mg is further preferable.
Examples of the Mg compound include MgO, Mg (OH) ₂ , MgSO ₄ , MgCl ₂ , and MgCO ₃ , and MgO, Mg (OH) ₂ and MgSO ₄ are preferable. These Mg compounds are preferably contained in an equivalent amount of 0.05 to 12.5%, more preferably 0.1 to 10%, and more preferably 0.15 to 7%, based on the carboxyl group in EMA (B). Is more preferably 0.5%, particularly preferably 0.5 to 7.5%.

Examples of the metal compound (D2) include zirconium halides such as zirconium oxychloride, zirconium hydroxychloride, zirconium tetrachloride, and zirconium bromide; zirconium salts of mineral acids such as zirconium sulfate, basic zirconium sulfate, and zirconium nitrate; Organic acids such as zirconium, zirconium acetate, zirconium propionate, zirconium caprylate, zirconium stearate, zirconium ammonium carbonate, sodium zirconium sulfate, zirconium ammonium acetate, zirconium sodium oxalate, sodium zirconium citrate, zirconium ammonium citrate, etc. And zirconium complex salts thereof, and ammonium zirconium carbonate is preferred. Examples of zirconium ammonium carbonate include "Zircosol AC-7" manufactured by Nutex Co., Ltd.

The coating material (C) used in the present invention may further contain an inorganic layer compound. By containing the inorganic layered compound, the gas barrier properties of the barrier layer and the gas barrier laminate can be further improved.
From the viewpoint of gas barrier properties, the content of the inorganic layered compound is preferably higher. However, the inorganic layered compound has a strong affinity for water and tends to absorb moisture. In addition, paint containing an inorganic layered compound tends to have a high viscosity, so that paintability is easily impaired. Further, when the content of the inorganic layered compound is large, the transparency of the formed gas barrier layer or the gas barrier laminate decreases.
Therefore, from these viewpoints, the amount of the inorganic layered compound is preferably 1 to 300 parts by weight, and more preferably 2 to 200 parts by weight based on 100 parts by weight of the total of PVA (A) and EMA (B). More preferably, it is even more preferably at most 100 parts by weight.

The term “inorganic layered compound” as used herein refers to an inorganic compound in which unit crystal layers overlap to form a layered structure, and in particular, a compound that swells and cleaves in a solvent is preferable.
Preferred examples of the inorganic layered compound include montmorillonite, beidellite, saponite, hectorite, sauconite, vermiculite, fluoromica, muscovite, paragonite, phlogopite, biotite, lepidrite, margarite, clintnite, anandite, chlorite, donba Site, Sdoite, Kukueite, Clinochlore, Shamosite, Nimite, Tetrasilylmica, Talc, Pyrophyllite, Nacrite, Kaolinite, Halloysite, Chrysotile, Sodium Teniolite, Zansophyllite, Antigorite, Diccite, Hydrotalcite And swellable fluoromica or montmorillonite is particularly preferred.

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

The swellable fluoromica-based mineral is most preferable in terms of whiteness, and is represented by the following formula.
α (MF) · β (aMgF ₂ · bMgO) · γSiO ₂ (where M represents sodium or lithium, α, β, γ, a and b each represent a coefficient, and 0.1 ≦ α ≦ 2, 2 ≦ β ≦ 3.5, 3 ≦ γ ≦ 4, 0 ≦ a ≦ 1, 0 ≦ b ≦ 1, a + b = 1.)

As a method for producing such a swellable fluoromica-based mineral, for example, silicon oxide, magnesium oxide and various fluorides are mixed, and the mixture is completely cooled in an electric furnace or a gas furnace at a temperature range of 1400 to 1500 ° C. There is a so-called melting method in which the fluorinated mica-based mineral crystal grows in the reaction vessel during the cooling process.

方法 Further, there is a method of using talc as a starting material and intercalating an alkali metal ion with the talc to obtain a swellable fluoromica-based mineral (Japanese Patent Laid-Open No. 2-149415). In this method, swellable fluoromica-based mineral can be obtained by mixing talc with alkali silicofluoride or alkali fluoride and subjecting it to a short heat treatment at about 700 to 1200 ° C. in a magnetic crucible.

At this time, the amount of alkali silicate or alkali fluoride mixed with talc is preferably in the range of 10 to 35% by weight of the whole mixture. It is not preferable because the yield decreases.

ア ル カ リ The alkali metal of the alkali silicofluoride or alkali fluoride is preferably sodium or lithium. These alkali metals may be used alone or in combination. In addition, in the case of potassium among alkali metals, a swellable fluoromica-based mineral cannot be obtained, but it can be used in combination with sodium or lithium, and in a limited amount, for the purpose of adjusting the swellability. It is.

Further, in the step of producing the swellable fluoromica-based mineral, it is also possible to mix a small amount of alumina to adjust the swellability of the generated swellable fluoromica-based mineral.

Montmorillonite is represented by the following formula and can be obtained by purifying naturally occurring products.
MaSi ₄ (Al _{2 -a} Mg _a ) O ₁₀ (OH) ₂ · nH ₂ O (wherein M represents a cation of sodium, a is 0.25 to 0.60, and bonds with an ion exchangeable cation between layers) The number of water molecules used can vary depending on conditions such as cation species and humidity, and is represented by nH ₂ O in the formula.)
Montmorillonite also includes the same type ion substitutes of magnesia montmorillonite, iron montmorillonite, and iron magnesia montmorillonite represented by the following formula group, and these may be used.
MaSi ₄ (Al _1.67-a Mg _{0.5 + a} ) O ₁₀ (OH) ₂ .nH ₂ O
MaSi ₄ (Fe _{2 -a} ³⁺ Mg _a ) O ₁₀ (OH) ₂ .nH ₂ O
MaSi ₄ (Fe _{1.67 -a} ³⁺ Mg _{0.5 + a} ) O ₁₀ (OH) ₂ .nH ₂ O
(In the formula, M represents a sodium cation, and a is 0.25 to 0.60.)

Normally, montmorillonite has ion-exchangeable cations such as sodium and calcium between its layers, but the content ratio varies depending on the production area. In the present invention, it is preferable that the ion-exchangeable cation between the layers is replaced with sodium by an ion-exchange treatment or the like. Further, it is preferable to use montmorillonite purified by water treatment.

The inorganic layered compound can be directly mixed with PVA (A) and EMA (B), but it is preferable to swell and disperse in a liquid medium in advance before mixing. The liquid medium for swelling and dispersion is not particularly limited.For example, in the case of a natural swelling clay mineral, water, methanol, ethanol, propanol, isopropanol, ethylene glycol, diethylene glycol, etc., alcohols, dimethylformamide, dimethyl sulfoxide , Acetone and the like, and alcohols such as water and methanol are more preferable.

The paint (C) used in the present invention contains a heat stabilizer, an antioxidant, a reinforcing material, a pigment, a deterioration inhibitor, a weathering agent, a flame retardant, a plasticizer, a mold release, as long as its properties are not significantly impaired. Agents, lubricants and the like may be added.

(4) Examples of the heat stabilizer, antioxidant and deterioration inhibitor include hindered phenols, phosphorus compounds, hindered amines, sulfur compounds, copper compounds, halides of alkali metals, and mixtures thereof.

Next, a method for producing the paint (C) used in the present invention will be described.
For example, a method in which PVA (A) and EMA (B) are separately prepared as aqueous solutions and mixed before use is preferable.
When the divalent or higher valent metal compound (D) is used, the coating (C) can be obtained by various methods. For example,
(1) When an aqueous solution of PVA (A) and an aqueous solution of EMA (B) are mixed, an aqueous solution of a divalent or higher-valent metal compound (D) or an aqueous solution of a divalent or higher-valent metal compound (D) is mixed;
(2) A metal compound (D) having a valency of 2 or more is dissolved in an aqueous solution of EMA (B) in advance, and this is mixed with an aqueous solution of PVA (A).
(3) A metal compound (D) having a valence of 2 or more is dissolved in an aqueous solution of PVA (A) in advance, and this is mixed with an aqueous solution of EMA (B).
And the like, and the method (2) is preferable.

The concentration (= solid content) of the paint (C) can be appropriately changed depending on the specifications of the coating apparatus and the drying / heating apparatus. However, if the solution is too dilute, a layer having a thickness sufficient to exhibit gas barrier properties is required. Coating becomes difficult, 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 coating material (C) is too high, it is difficult to obtain a uniform coating material, which tends to cause problems in coatability. From such a viewpoint, it is preferable that the concentration (= solid content) of the coating material (C) be in the range of 5 to 50% by weight.

[ Plastic substrate]
The gas barrier laminate of the present invention is obtained by applying the above-mentioned coating material (C) for forming a gas barrier layer directly on a plastic substrate or on a plastic substrate via an undercoat layer (hereinafter, also referred to as a UC layer). , Formed by heat treatment and then heat treatment in the presence of water.
The plastic substrate used here is a film-shaped substrate, a bottle, a cup, etc., manufactured from a thermoformable thermoplastic resin by means such as extrusion molding, injection molding, blow molding, stretch blow molding or draw molding. And a substrate having various container shapes such as a tray, and a film shape is preferable.
The plastic substrate may be composed of a single layer, or may be composed of a plurality of layers by, for example, co-extrusion or other lamination.

Examples of the thermoplastic resin constituting the plastic substrate include olefin-based copolymers, polyesters, polyamides, styrene-based copolymers, vinyl chloride-based copolymers, acrylic copolymers, and polycarbonates. Polymers, polyesters and polyamides are preferred.

Examples of the olefin copolymer include low-, medium- or high-density polyethylene, linear low-density polyethylene, polypropylene, ethylene-propylene copolymer, ethylene-butene-copolymer, ionomer, and ethylene-vinyl acetate copolymer. Coalescence, ethylene-vinyl alcohol copolymer, etc.
As polyester, polyethylene terephthalate, polybutylene terephthalate, polyethylene terephthalate / isophthalate, polyethylene naphthalate, etc.,
Examples of the polyamide include polyamides such as nylon 6, nylon 6,6, nylon 6,10, and meta-xylylene adipamide;
Examples of the styrene copolymer include polystyrene, styrene-butadiene block copolymer, styrene-acrylonitrile copolymer, styrene-butadiene-acrylonitrile copolymer (ABS resin), and the like.
As the vinyl chloride copolymer, polyvinyl chloride, vinyl chloride-vinyl acetate copolymer and the like,
Examples of the acrylic copolymer include polymethyl methacrylate and methyl methacrylate / ethyl acrylate copolymer.
These thermoplastic resins may be used alone or in combination of two or more.

The melt-moldable thermoplastic resin may contain, if desired, one or more additives such as pigments, antioxidants, antistatic agents, ultraviolet absorbers, lubricants, etc. per 100 parts by weight of the resin. It can be added in an amount of 0.001 part to 5.0 parts.
When a packaging material is formed using the gas barrier laminate of the present invention as described later, in order to ensure the strength of the packaging material, various reinforcing materials are used as a plastic base material constituting the gas barrier laminate. Can be used. That is, one of fiber reinforcing materials such as glass fiber, aromatic polyamide fiber, carbon fiber, pulp, and cotton linter, powder reinforcing material such as carbon black and white carbon, or flake-like reinforcing material such as glass flake and aluminum flake. One or two or more kinds can be blended in an amount of 2 to 150 parts by weight as a total amount per 100 parts by weight of the thermoplastic resin. For the purpose of further increasing the weight, heavy to soft calcium carbonate, mica, talc, kaolin, gypsum , One or more of clay, barium sulfate, alumina powder, silica powder, magnesium carbonate, etc., in a total amount of 5 to 100 parts by weight per 100 parts by weight of the thermoplastic resin according to a formulation known per se. No problem.
Furthermore, in order to improve the gas barrier properties, scaly inorganic fine powders such as water-swellable mica, clay and the like are formulated in a known amount in a total amount of 5 to 100 parts by weight per 100 parts by weight of the thermoplastic resin. There is no problem even if it is blended according to the formula.

[Undercoat layer]
The gas barrier laminate of the present invention is obtained by applying the above-mentioned coating material (C) for forming a gas barrier layer directly on a plastic substrate or via a UC layer onto a plastic substrate, and after heat-treating, further adding water. It is formed by heat treatment in the presence. Therefore, the UC layer used in the present invention will be described. The UC layer is located between the gas barrier layer and the plastic substrate, and mainly plays a role of improving the adhesion of the gas barrier layer.
The UC layer can be formed from various polymers such as urethane, polyester, acrylic, and epoxy, and a urethane UC layer is preferable.

For example, in the case of a urethane-based UC layer,
(1) A UC composition containing a polyol component such as a polyester polyol or a polyether polyol and a polyisocyanate component is coated on a plastic substrate, heated, and the polyol component and the polyisocyanate component are allowed to react with each other. Can be formed. By applying a solution of the coating material (C) on the UC layer and heating the solution, a laminate composed of the base material / UC layer / gas barrier layer can be obtained.
(2) The composition for UC is coated on a plastic substrate and dried to obtain a precursor of the UC layer in which the reaction between the polyol component and the polyisocyanate component is not completed, and the paint ( By applying and heating the solution of C), the formation of the UC layer and the formation of the gas barrier layer can be performed at one time to obtain the substrate / UC layer / gas barrier layer.
(3) Alternatively, after coating the composition for UC on a plastic substrate, the coating for forming a gas barrier layer is applied without heating, and the formation of the UC layer and the formation of the gas barrier layer are performed by heating. It is also possible to obtain a laminate composed of the base material / UC layer / barrier layer by performing the above at once.
The polyisocyanate contained in the composition for UC also reacts with the hydroxyl group in PVA (A) in the interface region with the gas barrier layer, thereby contributing to the improvement of adhesion and assisting the crosslinking of the gas barrier layer to improve the water resistance. Therefore, the methods (2) and (3) are preferable.

As the polyol component used for forming the UC layer, a polyester polyol is preferable, and the polyester polyol is obtained by reacting a polycarboxylic acid or a dialkyl ester thereof or a mixture thereof with a glycol or a mixture thereof. Polyester polyol to be used.
Examples of the polycarboxylic acid include aromatic polycarboxylic acids such as isophthalic acid, terephthalic acid, and naphthalenedicarboxylic acid, and aliphatic polycarboxylic acids such as adipic acid, azelaic acid, sebacic acid, and cyclohexanedicarboxylic acid.
Examples of the glycol include ethylene glycol, propylene glycol, diethylene glycol, butylene glycol, neopentyl glycol, 1,6-hexanediol, and the like.

These polyester polyols preferably have a glass transition temperature (hereinafter, referred to as Tg) of -50 ° C to 120 ° C, more preferably -20 ° C to 100 ° C, and still more preferably 0 ° C to 90 ° C. The preferred Tg of the polyester polyol is also related to the heat-curing conditions when the coating (C) is heat-cured after application. In the case of heat curing at a relatively low temperature, a polyester polyol having a relatively high Tg is preferable, and in the case of heat curing at a relatively high temperature, a polyester polyol having a relatively wide Tg from a low temperature to a high temperature can be suitably used. For example, when the paint (C) is cured by heating at 180 ° C, a polyester polyol having a Tg of about 70 to 90 ° C is preferable. On the other hand, when the coating material (C) is cured by heating at 200 ° C., a polyester polyol having a Tg of about 0 to 90 ° C. can be used.
The number average molecular weight of these polyester polyols is preferably from 1,000 to 100,000, more preferably from 3,000 to 50,000, and even more preferably from 10,000 to 40,000.

As the polyisocyanate used for forming the UC layer,
For example, 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, m-phenylene diisocyanate, p-phenylene diisocyanate, 4,4'-diphenylmethane diisocyanate, 2,4'-diphenylmethane diisocyanate, 2,2'- Diphenylmethane diisocyanate, 3,3'-dimethyl-4,4'-biphenylene diisocyanate, 3,3'-dimethoxy-4,4'-biphenylene diisocyanate, 3,3'-dichloro-4,4'-biphenylene diisocyanate, Aromatic polyisocyanates such as 1,5-naphthalene diisocyanate, 1,5-tetrahydronaphthalene diisocyanate, xylylene diisocyanate, tetramethyl xylylene diisocyanate,
Tetramethylene diisocyanate, 1,6-hexamethylene diisocyanate, dodecamethylene diisocyanate, trimethylhexamethylene diisocyanate, 1,3-cyclohexylene diisocyanate, 1,4-cyclohexylene diisocyanate, hydrogenated xylylene diisocyanate, lysine diisocyanate, isophorone diisocyanate, Aliphatic polyisocyanates such as 4,4'-dicyclohexylmethane diisocyanate and 3,3'-dimethyl-4,4'-dicyclohexylmethane diisocyanate;
Isocyanurate derived from the above polyisocyanate monomer, polyfunctional polyisocyanate compound such as buret and allophanate, or trimethylolpropane, terminal isocyanate group-containing compound obtained by reaction with a trifunctional or higher functional compound such as glycerin. Examples thereof include polyfunctional polyisocyanate compounds. Trifunctional isocyanurate, which is a trimer of hexamethylene diisocyanate (hereinafter also referred to as HMDI), is preferable.

The weight ratio between the polyester polyol and the polyisocyanate is preferably from 10:90 to 99: 1, more preferably from 30:70 to 90:10, and even more preferably from 50:50 to 85:15.

The thickness of the UC layer can be appropriately determined according to the intended use, but is preferably 0.1 μm to 10 μm, more preferably 0.1 μm to 5 μm, and more preferably 0.1 μm to 1 μm. Is particularly preferred. When the thickness is less than 0.1 μm, it is difficult to exhibit adhesiveness. On the other hand, when the thickness exceeds 10 μm, difficulty tends to occur in a production process such as coating.

The concentration of the polyesterol and the polyisocyanate in the composition for UC can be adjusted using an appropriate solvent, and the concentration is preferably in the range of 0.5 to 80% by weight of the total, preferably 1 to 80% by weight. More preferably, it is in the range of 70 to 70% by weight. If the concentration of the solution is too low, it is difficult to form a coating film having a required film thickness, and an excessive amount of heat is required during drying, which is not preferable. If the concentration of the solution is too high, the viscosity of the solution becomes too high, causing a problem that the operability is deteriorated at the time of mixing and coating.

Examples of the solvent that can be used in the composition for UC include, but are not limited to, toluene, MEK, cyclohexanone, solvesso, isophorone, xylene, MIBK, ethyl acetate, and butyl acetate.
In the UC layer, in addition to the above components, a well-known curing promoting catalyst, filler, softener, antioxidant, stabilizer, adhesion promoter, leveling agent, defoamer, plasticizer, inorganic filler, tackifier Coloring agents such as resins, fibers, pigments, and the like, and usable time extenders can also be used.

In order to form the UC layer and the barrier layer, the composition for forming each layer is coated on a plastic substrate by a roll coater method, a gravure method, a gravure offset method, a spray coating method, or a combination thereof. , UC layer to a desired thickness, but is not limited to these methods.
Moreover, after applying to an unstretched film and drying, it can also be stretched. For example, after drying, the film may be supplied to a tenter-type stretching machine to simultaneously stretch the film in the running direction and the width direction (simultaneous biaxial stretching) and heat-treat. Alternatively, the film may be stretched in the running direction of the film using a multi-stage heat roll or the like, and then a paint or the like may be applied, 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.
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 laminate.

[Gas barrier laminate]
The gas barrier laminate of the present invention is obtained by applying the above-mentioned coating material (C) for forming a gas barrier layer directly on a plastic substrate or via a UC layer onto a plastic substrate, and after heat-treating, further adding water. It is formed by heat treatment in the presence.
That is, after the coating material (C) is applied, an esterification reaction between PVA (A) and EMA (B) and the coating material (C) contain a divalent or higher valent metal compound (D) by heating once. In this case, a reaction between the metal compound (D) and PVA (A) or between the metal compound (D) and EMA (B) occurs, and the gas barrier laminate which is also referred to as a precursor of the final gas barrier laminate is produced. A body (hereinafter, this precursor may be referred to as “gas barrier laminate (1)”) is produced. By heat-treating the precursor in the presence of water, a gas-barrier laminate having significantly improved gas barrier properties can be obtained (hereinafter, the gas-barrier laminate heat-treated in the presence of water is referred to as a gas barrier laminate). Laminate (2) ").
As described in the section of the prior art, after applying the coating material, by heating, the hydroxyl group in PVA is sufficiently esterified with COOH in polyacrylic acid or EMA, or the functional group is reacted with the above functional group. In the past, it was thought that it was necessary to heat at a higher temperature or for a longer time in order to cause a crosslinking reaction with a metal. However, in order to improve the gas barrier properties under high humidity by introducing various cross-linking structures by heat, there is a practical limit from the viewpoint of the heat resistance of the plastic substrate itself and the barrier layer being formed.
On the other hand, the detailed mechanism of why the barrier property is improved is still unknown, but as described above, the coating (C) is applied, heated, and then heat-treated in the presence of water. A gas barrier laminate (2) having much better gas barrier properties than before can be obtained without thermal degradation of the plastic substrate itself and the barrier layer.

Depending on the ratio of PVA (A) to EMA (B), the presence or absence of a divalent or higher valent metal compound (D), and the content of a divalent or higher valent metal compound (D), etc. Since it can be affected, the preferable heat treatment conditions for the paint (C) cannot be unconditionally determined, but it is preferably performed at a temperature of 100 ° C or more and 300 ° C or less, more preferably 120 ° C or more and 250 ° C or less, and 140 ° C or more. 240 ° C or lower is more preferable, and 160 ° C or higher and 220 ° C or lower is particularly preferable.
Specifically, heat treatment is performed for 90 seconds or more in a temperature range of 100 ° C. to less than 140 ° C., for 1 minute or more in a temperature range of 140 ° C. to less than 180 ° C., or for 30 seconds or more in a temperature range of 180 ° C. to less than 250 ° C. Preferably,
It is more preferable to perform heat treatment for 2 minutes or more in a temperature range of 100 ° C or more and less than 140 ° C, or 90 seconds or more in a temperature range of 140 ° C or more and less than 180 ° C, or 1 minute or more in a temperature range of 180 ° C or more and 240 ° C or more. Preferably,
It is particularly preferable to perform heat treatment for 4 minutes or more in a temperature range of 100 ° C or more and less than 140 ° C, or 3 minutes or more in a temperature range of 140 ° C or more and less than 180 ° C, or about 2 minutes in a temperature range of 180 ° C or more and less than 220 ° C. preferable.

If the temperature of the heat treatment is too low or the time is too short, the crosslinking reaction becomes insufficient, and the water resistance of the gas barrier laminate (1) becomes insufficient. Further, when the heat treatment is performed at a temperature exceeding 300 ° C., the formed barrier layer and the plastic base material are deformed, wrinkled and thermally decomposed, and as a result, physical properties such as gas barrier properties are easily reduced.
In addition, the longer the heat treatment time, the better the gas barrier properties under high humidity tend to be. However, the heat treatment time must be within one hour in consideration of productivity and deformation and deterioration of the base film due to heat. Is preferably within 30 minutes, and particularly preferably within 20 minutes.
For example, when PVA (A) / EMA (B) = 30/70 (weight ratio) and Mg (OH) ₂ is contained at 1 to 5% with respect to COOH in EMA (B), It is preferable to carry out heat treatment at 160 to 200 ° C. for about 15 seconds to 10 minutes.

Next, the obtained gas barrier laminate (1) may be heat-treated in the presence of water.
As a method of heat-treating the gas barrier laminate (1) in the presence of water, there are various methods as described below.
(1) Immerse the gas barrier laminate (1) in water (hot water).
(2) Water (hot water) is sprayed on the gas barrier laminate (1) in the form of a mist or shower.
(3) Put the gas barrier laminate (1) under high humidity.
(4) The gas barrier laminate (1) is exposed to water vapor. You may heat with a hot roll, blowing a steam.
These multiple methods can be combined.
The temperature of water used for the treatment and the environmental temperature are preferably 90 ° C or higher, more preferably 95 ° C or higher, further preferably 100 to 140 ° C, and more preferably 110 to 130 ° C. Most preferred. The processing time is preferably 1 minute or more, more preferably 10 minutes or more, and most preferably 20 minutes or more. It is preferable that the water temperature and the environmental temperature are higher and the treatment time is longer. However, from the viewpoints of productivity, economy, energy saving, etc., the temperature should be as high as about 140 ° C. and the time as long as about 1 hour. Realistic.

Although it cannot be said unconditionally because it differs depending on the processing conditions, the heat treatment in the presence of water reduces the oxygen permeability under high humidity to about 1 / 1.5 to 1/70 of the level before the processing. In addition, oxygen gas barrier properties can be improved.
For example, the oxygen permeability measured under conditions of 25 ° C. and 80% relative humidity is 13 cc · μm / m ² · 24 h · atm or less before treatment, and at best 3.1 cc · μm / m ² · 24 h · atm. The degree of permeability was reduced to 1.5 cc · μm / m ² · 24 h · atm or less, and in a good case, 0.05 cc · μm / m ² · 24 h · atm by heat treatment in the presence of water. Oxygen permeability can be reduced to a degree.

If it is necessary to retort (sterilize) with steam under pressure after storing the food in the container (= packaging material) among the containers (packaging material) for storing the food, this retort treatment is performed. The performance of the gas barrier layer constituting the packaging material can also be improved by utilizing it.
That is, a gas-barrier laminate (1) is obtained, a food packaging container is obtained using the same, and the food is accommodated, and then subjected to retort treatment (sterilization treatment) at 120 ° C. for 30 minutes with steam under pressure to obtain the food. It is possible to improve the gas barrier properties of the gas barrier laminate (1) constituting the packaging container and to provide the gas barrier laminate (2).

Hereinafter, the present invention will be described specifically with reference to Examples and Comparative Examples, but the present invention is not limited to only these Examples.

<Oxygen permeability>
The film subjected to only the heat treatment was left in an atmosphere of 25 ° C. and 80% RH, and then the oxygen permeability at 25 ° C. and 80% RH was obtained using an oxygen permeation tester OX-TRAN TWIN manufactured by Modern Control. Similarly, after the heat treatment, the film subjected to the heat treatment in the presence of water was measured for oxygen permeability at 25 ° C. and 80% RH after the treatment. Specifically, oxygen gas and nitrogen gas (carrier gas) humidified at 25 ° C. and 80% RH were used.

The oxygen permeability of the film (= barrier layer) formed from the gas barrier layer forming paint (C) containing PVA (A) and EMA (B) was determined by the following formula.
1 / P _total = 1 / P _film + 1 / P _PET
However,
P _total : a laminated film composed of a film (= barrier layer) formed from a coating material (C) for forming a gas barrier layer containing PVA (A) and EMA (B), and a base film (polyethylene terephthalate film) layer Oxygen permeability. When having a UC layer, the oxygen permeability of the film (= barrier layer), the UC layer and the base film.
P _film : Oxygen permeability of the film layer formed from the gas barrier layer forming paint (C) containing PVA (A) and EMA (B).
P _PET : oxygen permeability of the substrate film (polyethylene terephthalate film) layer. When having a UC layer, the oxygen permeability of the UC layer and the base film.

Comparative Example 1 Example 1
Polyester (manufactured by Toyobo Co., Ltd., Byron 200 (Tg67 ° C., Mn = 17000) dissolved in a mixed solvent of toluene / MEK) and polyisocyanate (Sumitomo Chemical Co., Ltd., Sumidur 3300) were mixed with polyester and poly The weight ratio of the isocyanate was adjusted to 60/40 to obtain a mixed solution. To this mixed solution, a 1% MEK solution of dibutyltin laurylate, MEK and ethyl acetate were mixed to obtain a primer composition (= composition for forming a UC layer) having a solid content of about 14%.

PVA (Poval 124 (polyvinyl saponification degree: 98 to 99%, average degree of polymerization: about 2400), manufactured by Kuraray Co., Ltd.) was dissolved in hot water, and then cooled to room temperature to obtain a PVA aqueous solution. Separately, an EMA (weight average molecular weight: 100,000) aqueous solution in which Mg (OH) ₂ was dissolved was adjusted so that the COOH equivalent was 4.4%.
The PVA aqueous solution and the EMA aqueous solution were mixed so that the weight ratio of PVA and EMA was as shown in Table 1, to obtain a mixed solution having a solid content of 10% by weight (= a coating material for forming a barrier layer).

The above primer composition was coated on a biaxially stretched polyester film (thickness: 12 μm) with a bar coater No. 4 and dried in an electric oven at 80 ° C. for 30 seconds to form a film having a thickness of 0.5 μm, thereby obtaining a laminated film. The above-mentioned PVA / EMA mixed solution was coated on this laminated film with a bar coater No. 6 and dried at 80 ° C. for 2 minutes in an electric oven, followed by drying at 200 ° C. for 2 minutes and heat treatment in an electric oven to form a film having a thickness of 2 μm, thereby obtaining a laminated film 1 (Comparative Example). 1).
The laminated film 1 obtained in Comparative Example 1 was treated in hot water (120 ° C., 1.2 kgf / cm ² ) for 30 minutes using an autoclave to obtain a laminated film 2 (Example 1).
Table 1 shows the results of measuring the oxygen permeability of the laminated film and the film layer (= gas barrier layer) obtained in Comparative Example 1 and Example 1.

Comparative Example 2 Example 2
A laminated film was obtained in the same manner as in Comparative Example 1 and Example 1, except that the hot water treatment conditions were 105 ° C. and 0.3 kgf / cm ² . Table 1 shows the results of measuring the oxygen permeability of the obtained laminated film and film layer.

[Comparative Example 3] [Example 3]
An EMA aqueous solution in which Ca (OH) ₂ was dissolved was adjusted so that the COOH equivalent was 2.5%. A laminated film was obtained in the same manner as in Comparative Example 1 and Example 1, except that the obtained aqueous solution was used. Table 1 shows the results of measuring the oxygen permeability of the obtained laminated film and film layer.

[Comparative Example 4] [Example 4]
An EMA aqueous solution in which the metal compound was not dissolved was prepared. A laminated film was obtained in the same manner as in Comparative Example 1 and Example 1, except that the obtained aqueous solution was used. Table 1 shows the results of measuring the oxygen permeability of the obtained laminated film and film layer.

[Comparative Example 5] [Example 5]
A laminated film was obtained in the same manner as in Comparative Example 1 and Example 1, except that the primer layer was not used. Table 1 shows the results of measuring the oxygen permeability of the obtained laminated film and film layer.

[Comparative Example 6] [Example 6]
Polyester (manufactured by Toyobo Co., Ltd., Byron GK-880 (Tg 84 ° C., Mn = 23000)) dissolved in a mixed solvent of toluene / MEK, and polyisocyanate (Sumitomo Chemical Co., Ltd., Sumidur 3300) were mixed with polyester. And the polyisocyanate were adjusted to have a weight ratio of 60/40 to obtain a mixed solution. This mixed solution was mixed with a 1% MEK solution of dibutyltin laurylate, MEK and ethyl acetate to obtain a primer composition having a solid content of about 14%.

PVA (Poval 124 (polyvinyl saponification degree: 98 to 99%, average degree of polymerization: about 2400), manufactured by Kuraray Co., Ltd.) was dissolved in hot water, and then cooled to room temperature to obtain a PVA aqueous solution. Separately, an EMA (weight average molecular weight: 100,000) aqueous solution in which Mg (OH) ₂ was dissolved was adjusted so that the COOH equivalent was 4.4%.
The PVA aqueous solution and the EMA aqueous solution were mixed so that the weight ratio of PVA and EMA was as shown in Table 1, to obtain a mixed solution having a solid content of 10% by weight.

The above primer composition was coated on a biaxially stretched polyester film (thickness: 12 μm) with a bar coater No. 4 and dried in an electric oven at 80 ° C. for 30 seconds to form a film having a thickness of 0.5 μm, thereby obtaining a laminated film. The above-mentioned PVA / EMA mixed solution was coated on this laminated film with a bar coater No. 6 and dried at 80 ° C. for 2 minutes in an electric oven, followed by drying at 200 ° C. for 2 minutes and heat treatment in an electric oven to form a film having a thickness of 2 μm, thereby obtaining a laminated film 1 (Comparative Example). 6).
The laminated film 1 obtained in Comparative Example 6 was treated in hot water (120 ° C., 1.2 kgf / cm ² ) for 30 minutes using an autoclave to obtain a laminated film 2 (Example 6).
Table 1 shows the results of measuring the oxygen permeability of the laminated film and the film layer obtained in Comparative Example 6 and Example 6.

[Comparative Examples 7 to 9] [Examples 7 to 9]
A laminated film was obtained in the same manner as in Comparative Example 6 and Example 6, except that the drying and heat treatment conditions were set to 180 ° C. for 2 minutes, 160 ° C. for 2 minutes, or 140 ° C. for 2 minutes as shown in Table 1.
Table 1 shows the results of measuring the oxygen permeability of the obtained laminated film and film layer.

[Comparative Examples 10 to 12] [Examples 10 to 12]
The aqueous PVA solution used in Example 1 and the aqueous EMA solution used in Example 1 were mixed so that the weight ratio of PVA and EMA became as shown in Table 1, to obtain a mixed solution having a solid content of 10% by weight. . A laminated film was obtained in the same manner as in Comparative Example 1 and Example 1, except that the obtained aqueous solution was used.
Table 1 shows the results of measuring the oxygen permeability of the obtained laminated film and film layer.

[Comparative Examples 13 to 14] [Examples 13 to 14]
As shown in Table 1, an EMA aqueous solution in which Mg (OH) ₂ was dissolved was adjusted so that the COOH equivalent became 1.1% or 8.8%. A laminated film was obtained in the same manner as in Comparative Example 1 and Example 1, except that the obtained aqueous solution was used.
Table 1 shows the results of measuring the oxygen permeability of the obtained laminated film and film layer.

[Comparative Example 15] [Example 15]
A laminated film was obtained in the same manner as in Comparative Example 1 and Example 1, except that the drying and heat treatment conditions were changed to 240 ° C. for 2 minutes. Table 1 shows the results of measuring the oxygen permeability of the obtained laminated film and film layer.

[Comparative Example 16] [Example 16]
A laminated film was obtained in the same manner as in Comparative Example 6 and Example 6, except that the drying and heat treatment conditions were changed to 240 ° C. for 2 minutes. Table 1 shows the results of measuring the oxygen permeability of the obtained laminated film and film layer.

[Comparative Example 17]
The laminated film 1 obtained in Comparative Example 1 was treated for 30 minutes in heated ion-exchanged water (120 ° C., 1.2 kgf / cm ² ) using an autoclave to obtain a laminated film 2 (Comparative Example 17).
Table 1 shows the results of measuring the oxygen permeability of the laminated film and the film layer (= gas barrier layer) obtained in Comparative Example 17.

[Comparative Example 18]
The laminated film 1 obtained in Comparative Example 1 was treated with distilled water (120 ° C., 1.2 kgf / cm ² ) heated in an autoclave for 30 minutes to obtain a laminated film 2 (Comparative Example 18).
Table 1 shows the results of measuring the oxygen permeability of the laminated film and the film layer (= gas barrier layer) obtained in Comparative Example 18.

As shown in Comparative Examples 15 to 16 and Comparative Examples 6 to 9, only the heat treatment has a limit on the achievable oxygen permeation, and heating at 240 ° C. is no longer more effective than heating at 200 ° C. The transmittance could not be reduced.
On the other hand, even if the heat treatment is performed at a lower temperature as shown in Examples 15 to 16 and Examples 6 to 9, the heat treatment is performed in the presence of water, so that the heat treatment is substantially below the limit value due to the heat treatment alone. Oxygen permeability can be reduced.
Further, as shown from Comparative Example 4 vs. Example 4 and Comparative Examples 1 to 3 vs. Examples 1 to 3, when the paint contains a divalent or higher valent metal compound, heat treatment is performed in the presence of water. Effect becomes more remarkable.

Claims (8)

A gas barrier layer-forming coating material (C) containing polyvinyl alcohol (A) and an ethylene-maleic acid copolymer (B) on a plastic substrate directly or on a plastic substrate via an undercoat layer. A method for producing a gas-barrier laminate, comprising applying, heat-treating, and heat-treating in the presence of water. The method for producing a gas barrier laminate according to claim 1, wherein the paint (C) contains a divalent or higher valent metal compound. The method for producing a gas barrier laminate according to claim 2, wherein the divalent or higher valent metal compound can react with a hydroxyl group or a carboxyl group. The method for producing a gas barrier laminate according to claim 2, wherein the divalent or higher metal is Mg. The method for producing a gas-barrier laminate according to claim 4, wherein the Mg compound is contained in an equivalent amount of 0.05 to 12.5% with respect to the carboxyl group in the ethylene-maleic acid copolymer (B). . The gas barrier laminate according to any one of claims 1 to 5, wherein the weight ratio of the polyvinyl alcohol (A) to the ethylene-maleic acid copolymer (B) is 90/10 to 10/90. Method. The method for producing a gas barrier laminate according to any one of claims 1 to 6, wherein the undercoat layer is formed from a polyester polyol having a glass transition temperature of 0 ° C or higher and a polyisocyanate. The method for producing a gas barrier laminate according to any one of claims 1 to 7, wherein the heat treatment is performed at 90 ° C or higher in the presence of water.