JP2000318034A - Production of gas barrier film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce a film hard to receive the influence of humidity and excellent in oxygen gas barrier properties. SOLUTION: A gas barrier film is produced by extruding a polyvinyl alcohol type polymer containing 19 mol% or less of a 4 or less C α-olefin unit onto a substrate film while pref. adjusting the viscosity thereof to 1-35,000 poise and stretching the polymer coated substrate film at least by 3 times or more before heat-treating the same at 120 deg.C or higher.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a method for producing a gas barrier film.

[0002]

2. Description of the Related Art Various methods are known as methods for obtaining an oxygen gas barrier film and a packaging material using the same. One of them is aluminum (hereinafter “Al”).
Abbreviated. ) Although foil has perfect oxygen gas barrier properties, pinholes tend to occur by itself, so that a method of obtaining a film by laminating is known. However, the film on which the aluminum foil is laminated is opaque, so that the contents are difficult to see and remain as a residue after incineration.
In addition, there is a problem that mixing of metals by a metal detector cannot be detected. A method of depositing aluminum, silica, or the like is also known, but also has a problem that a pinhole is easily generated due to bending or the like.

[0003] As another oxygen gas barrier film, a method of coating polyvinylidene chloride (hereinafter abbreviated as "PVDC") is known. PVD
C has almost no hygroscopicity and has good gas barrier properties even under high humidity, so it is coated on various substrates. As a substrate coated with PVDC,
Films such as biaxially oriented polypropylene (hereinafter abbreviated as "OPP"), biaxially oriented nylon (hereinafter abbreviated as "ON"), biaxially oriented polyethylene terephthalate (hereinafter abbreviated as "OPET"), cellophane, etc. Is used. However, PVDC-laminated films have the problem of producing hydrogen chloride gas when incinerated as municipal waste.

As an oxygen gas barrier film, there is also known a method of applying completely saponified unmodified polyvinyl alcohol on the film or performing a heat treatment (Japanese Patent Application Laid-Open No. 6-32924). Polyvinyl alcohol film has a very good oxygen gas barrier property when the amount of moisture absorption is small, but has a strong hygroscopicity and a relative humidity of 70%.
Above this level, the oxygen gas barrier properties decrease sharply. Further, these polyvinyl alcohol films are usually applied as a solution of about several% to about 10% using a gravure coat, a roll coat, or the like. The thickness of the gas barrier layer after application and drying is several microns, and the gas barrier property is poor. When stretching is performed to improve the gas barrier layer, the gas barrier layer becomes 1 μm or less, and there is a problem that the stretching effect cannot be substantially obtained. It is known to use an ethylene / vinyl alcohol copolymer (hereinafter abbreviated as “EVOH”) in which more than 20 mol% of ethylene is copolymerized in order to improve the moisture absorption and stretchability of polyvinyl alcohol. Kaihei 5-116259). However, in this case, there is a problem in that if the degree of stretching is insufficient or if the degree of ethylene modification is increased in order to improve the stretchability, the melting point of the resin is lowered and sufficient heat treatment cannot be performed.

[0005]

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for producing a gas barrier film which is hardly affected by humidity and can obtain a coating film having excellent oxygen gas barrier properties. .

[0006]

Means for Solving the Problems The present inventors have conducted intensive studies on a method of manufacturing a gas barrier film which is a material that can substitute for PVDC, is less affected by humidity, and has excellent oxygen gas barrier properties. A gas barrier, comprising: extruding a polyvinyl alcohol-based polymer containing 19 mol% or less of α-olefin units of 4 or less onto a base film, and then subjecting it to stretching at least three times and heat treatment at 120 ° C. or more. The present inventors have found a method for producing a conductive film, and have completed the present invention.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION First, a polyvinyl alcohol-based polymer used for producing the gas barrier film of the present invention will be described in detail. The polyvinyl alcohol-based polymer used in the present invention is a polyvinyl alcohol-based polymer containing 19 mol% or less of α-olefin units having 4 or less carbon atoms. As the type of α-olefin, ethylene and propylene are preferable, and ethylene is particularly preferable. The modification degree of the α-olefin unit having 4 or less carbon atoms is
It is 19 mol% or less, preferably 3 to 19 mol%, more preferably 5 to 18 mol%. If it exceeds 19 mol%, the melting point of the polyvinyl alcohol-based polymer decreases, and a part of the crystal is melted by heat treatment after coating, thereby deteriorating the barrier property. When the content is 3 mol% or more, excellent oxygen gas barrier properties are exhibited at a high relative humidity of about 70% or more, and the stretching effect is sufficiently exhibited.

The degree of saponification of the polyvinyl alcohol polymer of the present invention is preferably from 90 to 99.99 mol%, more preferably from 97 to 99.95 mol%, further preferably from 99 to 99.90 mol%. The degree of saponification is 99.99
If it exceeds mol%, it is difficult to obtain industrially,
If the saponification degree is less than 90 mol%, it is difficult to obtain a sufficient gas barrier property.

The degree of polymerization of the polyvinyl alcohol polymer of the present invention is preferably 2000 or less, more preferably 1 or less.
750 or less, more preferably 100 to 1500, particularly preferably 200 to 1400. 2000 degree of polymerization
When it exceeds, the viscosity at the time of coating becomes too high, and the coating property decreases. When the degree of polymerization is less than 100, the strength is reduced, and pinholes are easily generated. The degree of polymerization of the polyvinyl alcohol-based polymer is a value measured based on JIS K6726.

The polyvinyl alcohol-based polymer of the present invention is more preferably a polyvinyl alcohol-based polymer containing not more than 19 mol% of an α-olefin having 4 or less carbon atoms and not more than 5 mol% of a silyl group-containing unit. . The content of the silyl group-containing unit is 5 mol% or less, preferably 3 mol% or less, more preferably 0.1 mol% to
1.5 mol%. If the content of the silyl group-containing unit exceeds 5 mol%, the stability of the aqueous polyvinyl alcohol-based polymer solution will be significantly reduced. As a method for containing a silyl group, a method using vinylalkoxysilane (vinyltrimethoxysilane, vinyltriethoxysilane, etc.) as a copolymer component is preferable. The polyvinyl alcohol polymer of the present invention can be obtained by a conventionally known method.

The polyvinyl alcohol polymer of the present invention preferably contains 0.01 to 2% by weight of sodium acetate. The content of sodium acetate is more preferably 0.02 to 1% by weight, and still more preferably 0.1% by weight.
03 to 0.5% by weight, particularly preferably 0.03 to 0.4%
5% by weight. The content of sodium acetate is 0.01 to
When the content is out of the range of 2% by weight, it is difficult to obtain a sufficient gas barrier property.

Next, the coating liquid of the polyvinyl alcohol-based polymer of the present invention will be described. The viscosity at the time of application to the base film is preferably 1 to 35,000 poise. The viscosity of the coating polymer varies depending on the degree of polymerization of the polymer, the temperature of the polymer, and the concentration of the coating solution, and it is more preferable that the following formula is satisfied.

(1) When 20 ° C. ≦ T ≦ 120 ° C.

0.2 × (P / T) ≦ viscosity (poise) ≦ 5
00 × (P / T)

(This viscosity is a value measured under a shear rate of 10 cm ^-1 )

(2) When 120 ° C. <T ≦ 250 ° C.

500 × (P / T) <viscosity (poise) ≦ 5
000 × (P / T)

(This viscosity is a value measured under a shear rate of 1000 cm ^-1 ) [where T: temperature of coating polymer or coating solution, P: viscosity average degree of polymerization of coating polymer]

The preferred range of the coating temperature in (1) is 50 to 50.
110 ° C, more preferably 70 to 100 ° C
It is. The preferable range of the coating temperature in (2) is 140.
To 240 ° C, and a more preferred range is 180 to 23.
0 ° C.

It is preferable to adjust the concentration of the polyvinyl alcohol-based polymer so as to satisfy the above relational expression, and the concentration is selected from the range of 15 to 100% by weight. A coating polymer solution concentration of 100% means a dry polymer containing no solvent. A preferred concentration is 20% or more and 9
0% or less, more preferably 50% or less. By using a hydrated or aqueous solution of a polyvinyl alcohol polymer having such a concentration, a uniform coating layer can be obtained. Water is suitably used as the solvent. Further, it does not hinder the use of a mixed solvent with methanol, ethanol, isopropyl alcohol, n-propyl alcohol, etc., but isopropyl alcohol and n-propyl alcohol are preferably used as a mixed solvent with water in view of the boiling point. Can be

A plasticizer, a melting point depressant and the like may be added to the coating polymer liquid. These include polyhydric alcohols such as glycerin, diglycerin and pentaerythritol. The amount of these additives is usually 10% by weight or less based on the polyvinyl alcohol-based dry polymer of the present invention. Further, an antifungal agent, an antiseptic and the like can be added to the coating solution.

The method for preparing the coating solution of the polyvinyl alcohol polymer of the present invention is not particularly limited. For example, if the solvent is 5
When the content is 0% or more, a method of heating and dissolving in advance, adjusting to a predetermined concentration and temperature, extruding from a die, and coating on a base film can be adopted. When almost no solvent is contained, a method of filling the polyvinyl alcohol-based polymer of the present invention into a single-screw or twin-screw extruder, heating and melting and extruding from a die can be adopted.

A crosslinking agent may be used in combination with the polyvinyl alcohol-based polymer coating solution of the present invention for the purpose of imparting water resistance. Examples of the crosslinking agent include an epoxy compound, an isocyanate compound, an aldehyde compound, a silica compound, an aluminum compound, a zirconium compound, and a boron compound. Among these, silica compounds such as colloidal silica and alkyl silicate are preferable. The amount of the crosslinking agent to be added is generally 5 to 60 parts by weight, preferably 10 to 40 parts by weight, and more preferably 15 to 30 parts by weight, based on 100 parts by weight of the polyvinyl alcohol polymer. If the amount of the crosslinking agent exceeds 60 parts by weight, the gas barrier properties may be adversely affected. It is also possible to add usually 5 to 60 parts by weight of an inorganic substance such as plate-like clay, mica and calcium carbonate to 100 parts by weight of the polyvinyl alcohol-based polymer.

Next, the polymer coating film of the present invention will be described. In the production method of the present invention, after applying the polyvinyl alcohol-based polymer of the present invention, it is necessary to stretch at least three times or more and to perform a heat treatment at 120 ° C. or more.

When the above-mentioned coating temperature is (1), the coating liquid is first dried to make the concentration of volatile components in the coating polymer 20% or less, preferably 10% or less. More preferred. Further, the content is preferably 0.1% or more, more preferably 1% or more, and most preferably 2% or more. Stretching can be performed with a volatile content higher than this, but bubbles may be generated due to evaporation of the volatile content, and it may be difficult to obtain a uniform coating film. The drying temperature at this time is not particularly limited, but is 70 to 110 ° C. in consideration of productivity. Similarly, when the coating temperature is (2), the volatile concentration is preferably 20% or less. However, when the solvent concentration is already 20% or less in the state of the coating liquid, it is not necessary to provide a drying step. Absent.

The thickness of the coating film of the polyvinyl alcohol-based polymer of the present invention having a volatile content of 20% or less is not particularly limited, but it is required to be 10 μm or more, preferably 15 μm or more, and more preferably, in consideration of subsequent stretching. 20 μm-10
0 μm. Forming a coating film of 100 μm or more is disadvantageous in cost.

Next, stretching will be described. Stretching may be performed immediately after the above-mentioned coating film of the polyvinyl alcohol-based polymer of the present invention having a volatile content of 20% or less is formed. Particularly, when the temperature of the polymer coating liquid is (2), the stretching is performed. It is desirable to temporarily cool to 100 ° C. or lower before the process. The stretching temperature is suitably selected from 90 to 230 ° C., and is usually equal to or lower than the heat treatment and heat setting temperature.

The stretching direction may be either vertical or horizontal in the film forming direction, or biaxial stretching may be performed both vertically and horizontally.
In this case, there are no restrictions on the stretching ratio in the vertical and horizontal directions, the order of the stretching, and the like, and there is no hindrance to changing the stretching temperature by the vertical and horizontal stretching. Preferably, however, it is uniaxial stretching in the horizontal direction or simultaneous biaxial stretching in the vertical and horizontal directions. The stretching ratio needs to be 3 times or more. It is preferably at least 5 times, more preferably at least 9 times, particularly preferably at least 12 times. The stretching ratio in this case is a value determined from the thickness of the coating film before stretching and the thickness of the coating film after stretching. The stretching ratio is preferably 50 times or less, and more preferably 40 times or less.

Next, the heat treatment will be described. The heat treatment temperature needs to be 120 ° C. or more, and preferably 1
It is 40 ° C or higher, more preferably 150 to 240 ° C, particularly preferably 160 to 200 ° C. In the heat treatment, when the above-mentioned stretching temperature is 120 ° C. or more, the heat treatment may be performed simultaneously with the stretching, or a heat fixing step may be provided after the stretching, and the heat treatment may be performed there. The time of the heat treatment is not particularly limited as long as the polymer reaches the heat treatment temperature, but is about 10 seconds to 5 minutes. The heat treatment is preferably performed in air.

The gas barrier film obtained by the production method of the present invention has an oxygen permeation amount measured at 20 ° C. and 90% RH in terms of the thickness of the polyvinyl alcohol-based polymer coating layer of the present invention of 2 μm. 30cc / m ² · day · at
m, and preferably 15 cc / m ² · day · atm or less, especially 1
Oxygen gas barrier properties of 0 cc / m ² · day · atm or less can be achieved.

As the base film in the production of the gas barrier film of the present invention, a polyolefin film,
Examples include a polyester film and a polyamide film. For base films such as polyolefin films, polyester films and polyamide films,
It is preferable to contain silicon (Si). The content of silicon is preferably 2% by weight or less, more preferably 1% by weight or less, and even more preferably 0.1 to 0.5% by weight.
When the silicon content is 0.1 to 2% by weight, the adhesion between the polyolefin film, the polyester film and the polyamide film and the film made of the polymer for film application is improved. Silicon is usually added in the form of a silica compound, and a known silica compound such as silicon oxide or alkyl silicate is used. Among these, colloidal silica (SiO ₂ ) is preferably used. As a method for adding the silica compound to the base film, a method of mixing the silica compound in the resin in advance at the time of forming the base film is generally used.

The thickness (final thickness in the case of stretching) of the base film is preferably 5 to 100 μm.

An adhesive component layer may be formed between the polyvinyl alcohol-based polymer layer of the present invention and the substrate film layer for the purpose of improving adhesiveness. The adhesive component is
Before applying the aqueous solution of the polymer for film application, it can be applied to the surface of the base film or mixed with the aqueous solution of the polymer for film application before use. The type of the adhesive is not particularly limited, and a conventionally known adhesive is preferably used.
Isocyanate type, urethane type, polyester type, imine type and the like are used.

In the gas barrier film of the present invention, a heat seal resin layer is usually formed on a polyvinyl alcohol polymer film layer. The formation of the heat seal resin layer is usually performed by an extrusion lamination method or a dry lamination method. Heat sealing resins include high density polyethylene (HDPE), low density polyethylene (LDPE), and linear low density polyethylene (LLD).
Polyethylene resins such as PE) and polypropylene (P
P) resin, ethylene-vinyl acetate copolymer, ethylene
α-olefin random copolymers, ionomer resins and the like can be used. Further, an adhesive layer may be provided between the polyvinyl alcohol-based polymer film layer and the heat seal resin layer.

[0035]

EXAMPLES The present invention will be specifically described with reference to Examples and Comparative Examples, but the present invention is not limited to these. In the following Examples and Comparative Examples, “parts”
And "%" means a weight basis unless there is particular notice. Further, the oxygen permeation amount (OTR) of the polyvinyl alcohol coating film (laminate of the substrate and the polyvinyl alcohol) (unit: cc / m ² · day · atm)
Means that the laminate is kept at a temperature of 20 ° C. and a relative humidity of 90% for 7 days.
After humidity control for a day, the measurement was performed. The oxygen permeation amount shown below is a value obtained by converting the thickness of the polymer for film application into 2 μm.

Example 1 Degree of polymerization 1050, degree of saponification 99.0 mol%, degree of ethylene modification 6.5 mol%, amount of sodium acetate contained 0.4% by weight
Was dissolved at 90 ° C. to obtain a 20% aqueous solution. At this time, the solution viscosity was 9 poise. This solution was extruded at 90 ° C. onto a non-stretched polypropylene film provided with a 1 μm-thick isocyanate-based adhesive before being subjected to corona treatment and dried at 100 ° C. to obtain a 20 μm-thick polyvinyl alcohol gas barrier layer. . At this time, the water content of the gas barrier layer was 2% by weight based on polyvinyl alcohol. Next, the obtained film laminate (base unstretched polypropylene, adhesive,
A laminate made of polyvinyl alcohol) was mounted on a stretching machine, stretched uniaxially at 120 ° C., and heat-treated and heat-set at 160 ° C. for 1 minute in air. The thickness of the obtained polyvinyl alcohol gas barrier layer after the stretching heat treatment was 1.
It was 8 μm. (Stretch ratio = 20 / 1.8 = 11
Times). The film laminate subjected to the stretching heat treatment is heated at 20 ° C. for 9 hours.
After humidity control for 7 days at 0% RH, the gas barrier property was measured under the same conditions. As a result, the oxygen permeation amount was 5.7 cc / m ² ···
It was day-atm.

Example 2 Using the same polyvinyl alcohol as in Example 1, a solution was prepared under the same conditions. Next, this solution was applied on an unstretched nylon film and dried at 100 ° C. to a thickness of 15 μm.
Was obtained. At this time, the water content of the coat layer was 1.7% by weight. Next, this laminate was mounted on a stretching machine, stretched at 200 ° C. simultaneously in the vertical and horizontal directions, and heat-treated at 200 ° C. and heat-set for 2 minutes.
The thickness of the obtained polyvinyl alcohol layer after the heat treatment for stretching was 1.6 μm. (Stretching ratio = 15 / 1.6 = 9.
4 times). The film laminated body subjected to the stretching heat treatment is 20 ° C.
After humidity control under 90% RH for 7 days, the gas barrier property was measured under the same conditions. As a result, the oxygen permeation amount was 2.1 cc / m ^2.
* Day * atm.

Example 3 As a substrate film, a corona treatment was applied,
An experiment was performed in the same manner as in Example 2 except that an unstretched polyester film provided with a 5 μm isocyanate-based anchor coat layer was used. After the film laminate subjected to the stretching heat treatment was conditioned at 20 ° C. and 90% RH for 7 days, the gas barrier property was measured under the same conditions.
It was 2.3 cc / m ² · day · atm.

Example 4 Polyvinyl alcohol unmodified with ethylene was dissolved at 98 ° C. at a polymerization degree of 1700, a saponification degree of 99.6 mol%, a sodium acetate content of 0.2% by weight, and a 25% aqueous solution was obtained.
The solution viscosity at this time was 1600 poise. This solution was extruded at 90 ° C. onto a non-stretched polypropylene film provided with a 1 μm-thick isocyanate-based adhesive before being subjected to corona treatment and dried at 100 ° C. to obtain a 20 μm-thick polyvinyl alcohol gas barrier layer. . At this time, the water content of the gas barrier layer was 2.4% by weight based on polyvinyl alcohol. Next, the obtained film laminate (laminate consisting of unstretched polypropylene base material, adhesive, and polyvinyl alcohol) was mounted on a stretching machine,
The film was stretched in a uniaxial direction at 120 ° C., and heat-treated and heat-set at 160 ° C. for 1 minute. The thickness of the obtained polyvinyl alcohol gas barrier layer after the heat treatment for stretching was 2.2 μm. The film laminate subjected to the stretching heat treatment is heated at 20 ° C and 90 ° C.
After humidifying for 7 days at% RH, the gas barrier properties were measured under the same conditions. As a result, the oxygen permeation amount was 12 cc / m ² · da.
y · atm.

Example 5 A degree of polymerization of 500, a degree of saponification of 99.2 mol%, a degree of modification of ethylene of 17.8 mol%, a degree of modification of a silyl group by copolymerization of vinyltrimethoxysilane of 0.25 mol%, and an amount of sodium acetate of 0.1. 3% by weight of polyvinyl alcohol was put into a mixed solvent of water / n-propyl alcohol = 6/4 (weight ratio) and dissolved at 85 ° C. to obtain a 25% aqueous solution. At this time, the solution viscosity was 8 poise. This solution was extruded at 85 ° C. onto a non-stretched polypropylene film provided with a 1 μm-thick isocyanate-based adhesive on a corona treatment in advance and dried at 100 ° C. to obtain a polyvinyl alcohol barrier layer having a thickness of 21 μm. At this time, the volatile content of the barrier layer was 1.3 to polyvinyl alcohol.
% By weight. Next, the obtained film laminate (laminate composed of unstretched polypropylene base material, adhesive, and polyvinyl alcohol) was mounted on a stretching machine, stretched uniaxially at 120 ° C., heat-treated at 160 ° C. for 1 minute, and heat-set. Was given. The thickness of the obtained polyvinyl alcohol gas barrier layer after the stretching heat treatment was 1.5 μm. (Stretch ratio = 2
1 / 1.5 = 14 times). After the film laminate subjected to the stretching heat treatment was conditioned at 20 ° C. and 90% RH for 7 days, the gas barrier property was measured under the same conditions.
It was 1.2 cc / m ² · day · atm.

Example 6 An isocyanate-based adhesive was melt-extruded on an unstretched polypropylene film that had been corona-treated in advance.
On top of that, the polyvinyl alcohol used in Example 5 was melted at 210 ° C. in a uniaxial extruder and extruded from a die to laminate a laminate (unstretched polypropylene / adhesive / polyvinyl alcohol). At this time, the resin viscosity was 9,000 poise. The barrier layer thickness of the obtained polyvinyl alcohol was 14 μm, and the volatile content was 0.2% by weight. Next, the obtained film laminate was mounted on a stretching machine and stretched uniaxially at 120 ° C.
Heat treatment and heat setting were performed at 0 ° C. for 1 minute. The thickness of the obtained polyvinyl alcohol gas barrier layer after the stretching heat treatment was 1.3 μm. (Stretch ratio = 14 / 1.3 = 1
0.8 times). Twenty-five film laminates subjected to stretching heat treatment
After humidity control for 7 days at 90 ° C. and 90% RH, the gas barrier properties were measured under the same conditions.
m ² · day · atm.

Example 7 An isocyanate-based adhesive was melt-extruded on an unstretched polypropylene film previously subjected to corona treatment.
Further, the polyvinyl alcohol used in Example 1 was melted at 230 ° C. in a uniaxial extruder and extruded from a die to laminate a laminate (unstretched polypropylene / adhesive / polyvinyl alcohol). The resin viscosity at this time was 30,000 poise. The obtained polyvinyl alcohol had a barrier layer thickness of 16 μm and a volatile content of 0.1% by weight. Next, the obtained film laminate was mounted on a stretching machine and stretched uniaxially at 120 ° C.
Heat treatment and heat setting were performed at 60 ° C. for 1 minute. The thickness of the obtained polyvinyl alcohol gas barrier layer after the stretching heat treatment was 1.8 μm. (Stretch ratio = 16 / 1.8 =
8.9 times). Twenty-five film laminates subjected to stretching heat treatment
After humidity control for 7 days at 90 ° C. and 90% RH, the gas barrier properties were measured under the same conditions.
m ² · day · atm.

Comparative Example 1 A film laminate was obtained in the same manner as in Example 1 except that the stretching temperature was 100 ° C., and the heat treatment and heat setting were performed at 100 ° C. The thickness of the obtained polyvinyl alcohol gas barrier layer was 2.1 μm. This was humidified at 20 ° C. and 90% RH for 7 days, and the gas barrier property was measured under the same conditions. As a result, the oxygen permeation amount was 56 cc / m ² · day · at.
m.

Comparative Example 2 A film laminate was obtained in the same manner as in Example 2, except that only heat treatment was performed at 200 ° C. without stretching. The thickness of the obtained polyvinyl alcohol gas barrier layer was 14 μm. This was humidified at 20 ° C. and 90% RH for 7 days, and the gas barrier properties were measured under the same conditions. As a result, the oxygen permeation amount was 47 cc / m ² · day · atm.

Comparative Example 3 Polyvinyl alcohol having a degree of polymerization of 550, a degree of saponification of 99.0 mol%, a degree of ethylene modification of 8.5 mol%, and a sodium acetate content of 0.4% by weight was dissolved at 90 ° C.
To give a 7% aqueous solution. At this time, the solution viscosity was 0.1 poise. This solution was subjected to a corona treatment in advance, and an isocyanate-based adhesive was provided thereon at a thickness of 1 μm.
And dried at 100 ° C. to obtain a polyvinyl alcohol barrier layer having a thickness of 4 μm. At this time, the water content of the barrier layer was 1.2% by weight based on polyvinyl alcohol. Next, the obtained film laminate (laminate comprising unstretched polypropylene, adhesive, and polyvinyl alcohol) was attached to a stretching machine, and stretched uniaxially at 120 ° C.
Although heat treatment and heat setting were performed at 160 ° C. for 1 minute, delamination, cracks, and the like were observed in the polyvinyl alcohol gas barrier layer, and the oxygen permeation amount could not be measured.

Comparative Example 4 In Example 1, instead of the polyvinyl alcohol solution, ethylene having a polymerization degree of 1050, a saponification degree of 99.0 mol%, an ethylene modification degree of 27 mol%, and a sodium acetate content of 0.4 wt% was used. Using a vinyl alcohol copolymer, melt this at 230 ℃ in a single screw extruder, from the die,
A corona treatment was performed in advance, and an isocyanate-based adhesive was extruded on a non-stretched polypropylene film having a thickness of 1 μm to obtain an ethylene-vinyl alcohol copolymer gas barrier layer having a thickness of 20 μm. The obtained laminated film was stretched and heat-treated under the same conditions as in Example 1, but the gas barrier layer had streaks and tears.

Comparative Example 5 Polyvinyl alcohol unmodified at 98 ° C. was dissolved at 98 ° C. to obtain a 25% aqueous solution.
The solution viscosity at this time was 1600 poise. This solution was extruded at 90 ° C. onto a biaxially oriented polypropylene film (OPP) which had been previously subjected to corona treatment and provided thereon with an isocyanate-based adhesive having a thickness of 1 μm.
The resultant was dried at ℃ to obtain a polyvinyl alcohol gas barrier layer having a thickness of 20 μm. At this time, the water content of the gas barrier layer was 2.4% by weight based on polyvinyl alcohol. Next, the obtained film laminate (laminate composed of OPP, adhesive, and polyvinyl alcohol) was subjected to heat treatment and heat fixing at 160 ° C. for 1 minute. After heat-treating the heat-treated film laminate at 20 ° C. and 90% RH for 7 days, the gas barrier properties were measured under the same conditions.
It was cc / m ² · day · atm.

[0048]

According to the production method of the present invention, it is possible to obtain a film which is hardly affected by humidity and has excellent oxygen gas barrier properties.

Claims (8)

[Claims] 1. Extrusion of a polyvinyl alcohol-based polymer containing 19 mol% or less of α-olefin units having 4 or less carbon atoms onto a base film, followed by stretching at least 3 times or more and heat treatment at 120 ° C. or more. A method for producing a gas-barrier film, which is performed. 2. The method for producing a gas barrier film according to claim 1, wherein the polyvinyl alcohol polymer is extruded onto the substrate film at a viscosity of 1 poise to 35,000 poise. 3. The method for producing a gas barrier film according to claim 1, wherein the polyvinyl alcohol-based polymer is a polyvinyl alcohol-based polymer containing 3 to 19 mol% of α-olefin units having 4 or less carbon atoms. . 4. The method for producing a gas barrier film according to claim 1, wherein the α-olefin unit having 4 or less carbon atoms is an ethylene unit. 5. The method for producing a gas barrier film according to claim 1, wherein the polyvinyl alcohol-based polymer is a polyvinyl alcohol-based polymer having a degree of saponification of 90 to 99.99 mol%. 6. The method for producing a gas barrier film according to claim 1, wherein the polyvinyl alcohol-based polymer is a polyvinyl alcohol-based polymer containing 0.01 to 2% by weight of sodium acetate. 7. The method for producing a gas barrier film according to claim 1, wherein the polyvinyl alcohol-based polymer is a polyvinyl alcohol-based polymer containing 5 mol% or less of a silyl group-containing unit. 8. A method for extruding a hydrated or aqueous solution of a polyvinyl alcohol-based polymer onto a substrate film.
The method for producing a gas barrier film according to any one of the above.