JP2007254602A - Gas barrier film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a gas barrier film that can be suitably used as a packaging material in various kinds of fields such as food products, pharmaceuticals and medical products, precision electronic components and the like, is excellent in stability of a coating fluid, causes less deterioration in gas barrier properties under a high humidity condition even when a gas barrier layer is formed to become thinner and can be produced with stability while inhibiting the occurrence of cracks. <P>SOLUTION: The gas barrier film is formed by coating at least one side of a substrate formed of a plastic film with a coating fluid comprising a mixture of a hydrolyzate of an alkoxy silane and/or a polycondensate of an alkoxy silane with a polyvinyl alcohol and an organic acid having a pKa of 4.00 or less (25°C, 0.1 mol/dm<SP>3</SP>) added to the mixture in an amount of 0.5-15 wt.% (solids content ratio) based on the mixture. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a transparent gas barrier film used in the field of packaging foods, pharmaceuticals, precision electronic parts and the like.

  In recent years, packaging materials used in the packaging field of foods, pharmaceuticals, precision electronic components, etc. are used to maintain the taste and freshness by suppressing the alteration of contents, especially the oxidation of fats and oils and the alteration of proteins in foods. In addition, in pharmaceuticals, the effects of oxygen permeating through packaging materials are prevented in order to suppress the deterioration of active ingredients and maintain their efficacy, and in precision electronic parts, to suppress the corrosion of metal parts and prevent poor insulation. Therefore, it is required to have a gas barrier property to block gas (gas).

  For this purpose, polymer films that are generally said to have a relatively high gas barrier property such as polypropylene (KOP), polyethylene terephthalate (KPET), or ethylene vinyl alcohol copolymer (EVOH) coated with vinylidene chloride resin are used as gas barrier materials. In general, a packaging film using a gas barrier material as a gas barrier material or a deposited film in which a silicon oxide thin film such as silicon oxide (SiOx) is provided on a substrate made of a transparent polymer by means of vacuum deposition or the like is generally used. I came.

  However, the packaging film using the above-mentioned EVOH is easily affected by temperature and humidity, and the gas barrier property may be further lowered depending on the change. In addition, packaging films using vinylidene chloride resins such as KOP and KPET are said to be one of the causes of acid rain because they generate chlorine gas when incinerated after disposal. There is. In addition, a deposited film in which a silicon oxide thin film is provided on a substrate made of a transparent polymer by means such as vacuum deposition may easily crack the deposited film due to bending or the like, and as a result, gas barrier properties may be lowered.

Therefore, as a packaging film that overcomes these drawbacks, as a method for coating a film with a liquid composition comprising a water-soluble inorganic substance or polymer and developing a high gas barrier property, a hydrophilic polymer solution such as polyvinyl alcohol (PVA) A method of imparting gas barrier properties by mixing a hydrolyzed solution of metal alkoxide, coating the film, drying and heat-treating the polymer to interact between the hydrophilic polymer and the metal alkoxide has been proposed (Patent Document 1). . These methods combine the excellent gas barrier properties of metal oxides with the flexibility of polymers, and have high gas barrier properties and practicality that can withstand rough handling such as bending.
However, it is not easy to highly complex the hydrophilic polymer and the metal oxide, and there is a problem that the gas barrier property is impaired particularly when exposed to a high humidity for a long time.

  Therefore, in place of polyvinyl alcohol, those using a mixture of ethylene alcohol / vinyl alcohol copolymer with polyvinyl alcohol (Patent Document 2), those using modified polyvinyl alcohol as polyvinyl alcohol (Patent Document 3), etc. have been reported. In addition, a method of using an alkoxysilane having an imino group as a silane compound and aging after drying to form a gas barrier layer has been reported (Patent Document 4). As a result, although the gas barrier property showed a certain improvement, it was difficult to say that the gas barrier property was sufficiently improved especially when exposed to high humidity for a long time.

  The present inventors have previously proposed a gas barrier film that has overcome these drawbacks (Japanese Patent Application No. 2004-282296). The film has little deterioration in gas barrier properties due to the passage of time under high humidity even without providing an overcoat layer on the gas barrier layer. However, when the barrier layer is thinned, the gas barrier is stable under high humidity. In some cases, it may not be possible to express the properties, and if it is thick, cracks may occur depending on the drying conditions, and the work may be complicated for precise control of the drying conditions.

On the other hand, a sol-gel coating solution consisting of a hydrolyzed solution of metal alcoside and a hydrophilic polymer solution becomes a gel in several hours depending on the pH. Therefore, an acid or base is usually used as a pH adjuster or hydrolysis catalyst. This is added to give the coating solution a sufficient pot life (Patent Document 5). However, when an inorganic acid such as hydrochloric acid generally used as a hydrolysis catalyst is used, the stability of the coating liquid is good, but it does not improve the crack resistance of the gas barrier layer during drying. . Moreover, although the example which used organic acids, such as an acetic acid, as a hydrolysis catalyst instead of an inorganic acid is also reported (patent document 6), in order to obtain a stable coating liquid, it is necessary to increase addition amount, The As a result, there was a defect that the crack resistance of the coated film was lowered and the gas barrier property was lowered.
JP-A-4-345841 and JP-A-6-192454 JP 2001-219506 A JP 2004-143197 A JP 2002-292810 A Japanese Patent Laid-Open Nos. 4-80030 and 4-345841 JP 2002-60525 A

  The present invention solves the above-mentioned drawbacks, is excellent in the stability of the coating solution, has little deterioration in gas barrier properties under high humidity even when the coating layer is thin, and can be stably produced while suppressing cracks It is an object to provide a film.

The present inventors have found that the problem can be solved by adding a specific organic acid to the coating solution, and have completed the present invention.
That is, the invention described in claim 1 is represented by the general formula [1] (wherein R represents the same or different alkyl group having 1 to 4 carbon atoms, and n represents an integer of 0 to 10). An organic acid having a pKa of 4.00 (25 ° C., 0.1 mol / dm ³ ) or less is added to the mixture of the alkoxysilane and / or the hydrolyzate of the alkoxysilane polycondensate and polyvinyl alcohol. A gas barrier film in which 0.5 to 15% by weight (solid content ratio) added coating liquid is coated on at least one surface of a substrate made of a plastic film,
The invention according to claim 2 has a gas barrier film according to claim 1, further comprising an adhesive layer between the plastic film and the coat layer.
The invention according to claim 3 is the gas barrier film according to claim 1 or 2, wherein the plastic film is a stretched polyamide film.
It is.

The present invention is a gas barrier film that has excellent gas barrier properties, particularly oxygen barrier properties, and does not deteriorate oxygen barrier properties even under a long period of time at high humidity. This is advantageous in that it can be produced stably with cracks suppressed.
The feature of the present invention is that an organic acid having a pKa of 4.00 or less is used. Therefore, when using an organic acid such as acetic acid, butyric acid, valeric acid, propionic acid or the like having a pKa of 4.00 or more, an increase in the amount added to obtain a stable coating solution, a reduction in crack resistance associated therewith, a gas barrier There are no disadvantages such as a decrease in the properties and the residue of the organic acid in the gas barrier film, and there is no disadvantage of the occurrence of cracks when an inorganic acid such as hydrochloric acid or aluminum sulfate is used.

Hereinafter, the present invention will be described in detail.
The alkoxysilane and its polycondensate used in the present invention (hereinafter also simply referred to as alkoxysilane) are represented by the general formula [1] (wherein R represents the same or different alkyl group having 1 to 4 carbon atoms). , N represents an integer of 0 to 10.), and these can be used alone or in combination.
Further, the polyvinyl alcohol is not particularly limited, but 80% or more of saponified product is preferable, and more preferably completely saponified product is used. The completely saponified product is more compatible with the hydrolyzed product obtained by hydrolyzing the alkoxysilane and forms a denser barrier layer. The degree of polymerization of polyvinyl alcohol is preferably 200 to 3,500.

The alkoxysilane is preferably hydrolyzed to a hydrolysis rate of 90% and then mixed with the polyvinyl alcohol solution.
Hydrolysis of the alkoxysilane is carried out by warming the alkoxysilane in a solution containing water, an inorganic acid and an organic solvent. At this time, polycondensation of the alkoxysilane hydrolyzate also occurs simultaneously. The amount of water used is 6 to 10 moles per silicon atom of alkoxysilane. When the amount is more than 10 mol, polycondensation of the hydrolyzed silicate proceeds too much and the solution gels. The gelled liquid cannot be uniformly mixed with the polyvinyl alcohol solution. On the other hand, when the amount is less than 6 mol, it is substantially difficult to achieve a hydrolysis rate of 90% or more of alkoxysilane.

Inorganic acids act as catalysts for the hydrolysis and polycondensation of alkoxysilanes. As the inorganic acid used, mineral acids such as hydrochloric acid and nitric acid and other inorganic acids are preferably used. The pH during hydrolysis is 0.5 to 3.5, preferably 2 to 2.7. If the pH is greater than 3.5, hydrolysis does not proceed. When the pH is less than 0.5, hydrolysis proceeds sufficiently, but at the same time, polycondensation proceeds remarkably and the solution gels.
The temperature at the time of hydrolysis is 30 to 60 ° C, preferably 40 to 55 ° C. If it is higher than 60 ° C., polycondensation proceeds and the solution gels. On the other hand, if the temperature is lower than 30 ° C., hydrolysis does not proceed sufficiently and a longer time is required, which is not practical. The hydrolysis time varies depending on the pH and temperature of the solution, but is generally 30 to 400 minutes.

Examples of the organic solvent to be used include methyl alcohol, ethyl alcohol, n-propyl alcohol, isopropyl alcohol, n-butanol and the like, and ethyl alcohol and isopropyl alcohol are particularly preferably used. The amount of the organic solvent is 0.3 to 3% by weight based on the weight of water used for hydrolysis. If the amount is more than 3% by weight, it is difficult to recover the organic solvent, and if the amount is less than 0.3% by weight, the solution gels when the alkoxysilane is hydrolyzed.
By the above method, it is possible to obtain a solution that does not gel despite the hydrolysis rate of 90% or more of alkoxysilane.

The mixture of the alkoxysilane hydrolyzed solution and the polyvinyl alcohol solution is 25 to 100% by weight, preferably 60 to 100% by weight, with respect to 100% by weight of silicon oxide (in terms of SiO ₂ ) in the hydrolyzed solution. It is. When the weight ratio of polyvinyl alcohol is lower than 25% by weight, not only the flexibility of the barrier layer is sufficient and cracks are easily generated, but also the gas barrier property is lowered. When it is larger than 100% by weight, the gas barrier property is lowered, which is not preferable.

In the present invention, an organic acid having a pKa of 4.00 (25 ° C., 0.1 mol / dm ³ ) or less is added to the above mixture to prepare a coating solution.
The organic acid to be used can be appropriately selected from organic acids having a pKa of 25 ° C. and 0.1 mol / dm ³ of 4.00 or less. From the viewpoint of the stability of the coating liquid, crack resistance, and gas barrier properties under high humidity. Therefore, glycolic acid (pKa = 3.66), lactic acid (pKa = 3.63), citric acid (pKa = 2.90), d-tartaric acid (pKa = 2.82) and the like are particularly preferable.

The addition amount of the organic acid is 0.5 to 15 parts by weight, preferably 1 to 5% by weight, based on 100% by weight of the solid content of the mixture. If it is less than 0.5% by weight, the coating solution is not sufficiently stable, and the effect of crack resistance of the coating layer during drying hardly appears. On the other hand, when the content is more than 15% by weight, the stability of the coating solution is good, but even if the coating layer is thick, it is difficult to exhibit good gas barrier properties.
The addition method of organic acid is arbitrary, for example, the method of adding to the mixture of the hydrolyzate of alkoxysilane and the polyvinyl alcohol solution, the method of adding the organic acid to the hydrolyzate of alkoxysilane and then mixing with the polyvinyl alcohol solution Etc.
This coating solution is very stable. In particular, when the addition amount of the organic acid is 5% by weight or more, it does not gel for 96 hours or more at room temperature, and can maintain the sol state.

  In order to apply the coating liquid thus prepared to a substrate made of a plastic film, a normal coating method can be used. For example, various printing methods such as reverse roll coating method, dip coating method, Mayer bar coating method, knife coating method, nozzle coating method, die coating method, spray coating method, curtain coating method, screen printing, gravure coating, etc. It is done. These may be combined.

  The base plastic film used in the present invention is a polyolefin resin such as polyethylene or polypropylene; a polyester resin such as polyethylene terephthalate, polyethylene isophthalate, polyethylene-2,6-naphthalate or polybutylene terephthalate; Polyether resins; Polyamide resins such as polyamide-6, polyamide-6,6, polymetaxylene adipamide; Vinyl resins such as polystyrene, poly (meth) acrylate, polyacrylonitrile, polyvinyl acetate; Polycarbonate Cellulose resin such as cellulose acetate; Polyimide; Polyetherimide; Polyphenylene sulfide; Polyethersulfone; Polysulfone; Ton; a films mainly composed of thermoplastic resins such as polyether ketone ketone. These thermoplastic resins may be a homopolymer or a copolymer. In addition, the plastic film used for this invention is not limited to the said thermoplastic resin, The non-thermoplastic film represented by the cellophane can also be used. As the film, either an unstretched film or a uniaxially or biaxially stretched film can be used, but a stretched polyamide film is most preferable from the viewpoint of ease of coating when coating the barrier layer and the strength of the barrier film.

After coating, the coating layer is dried and aged to form a gas barrier layer having high gas barrier properties even under high humidity.
Drying is performed at a dryer internal temperature of 200 ° C. or lower, preferably 100 to 150 ° C. for 1 to 30 seconds. When dried at a temperature higher than 200 ° C., fine voids are formed in the barrier layer due to rapid evaporation of the solvent, and the gas barrier properties are lowered. When the drying time is longer than 30 seconds, the volumetric shrinkage of the coating film becomes significant, and as a result, cracks occur in the coating film.
After drying, aging is performed at an ambient temperature of 20 to 80 ° C. for 24 hours or longer, preferably at 40 to 60 ° C. for 36 hours or longer. When the temperature is higher than 80 ° C., the flatness of the base material made of a plastic film is impaired, and processing suitability such as printability is deteriorated. Moreover, when it is lower than 20 ° C., a sufficient aging effect cannot be obtained.

The coating amount of the gas barrier layer (coat layer) is adjusted to 0.1 to 2.0 g / m ² , preferably 0.3 to 1.0 g / m ² (both after aging). When the amount is less than 0.1 g / m ² , the gas barrier property is not sufficiently exhibited. When the amount is more than 2.0 g / m ² , the volume shrinkage becomes remarkable and cracks are likely to occur.

  In the present invention, an adhesive layer can be provided between the substrate made of a plastic film and the coating layer as necessary. The adhesive layer contains a compound containing an isocyanate group, a carboxyl group, an acid anhydride group, an oxazolinyl group, a thioisocyanate group, and an epoxy group, and can be coated and dried by the coating method described above. .

Hereinafter, the present invention will be specifically described with reference to Examples and Comparative Examples.
For measuring the oxygen permeability, an oxygen permeability measuring apparatus model 8000 manufactured by Illinois was used. The measurement was performed at 20 ° C.-90% RH for 48 hours.

Examples 1-4
Ethyl Silicate 40 purified water 8.3 mol per mol of (Colcoat Co. SiO ₂ minutes 40%) silicon 1 atom, and a 1.3-fold isopropanol added to the weight of silicon oxide, aluminum sulfate Then, the pH was adjusted to 2.9, followed by hydrolysis at 55 ° C. for 3.5 hours with stirring. After cooling this solution, pure water was added to obtain a transparent solution containing 7% by weight of silicon oxide.
On the other hand, polyvinyl alcohol (manufactured by Kuraray Co., Ltd., PVA-117, saponification degree 98-99%, average polymerization degree 1100) was dissolved in pure water to obtain a 7% by weight aqueous solution.
After the above solution was mixed and stirred so that the weight ratio of polyvinyl alcohol and silicon oxide was 40/60, 3.3% by weight of glycolic acid was added to 100% by weight of the solid content of the mixture. Further, the mixture was stirred. The pH of the coating solution at this time was 3.0. This coating solution was stable for 96 hours or more at room temperature and did not gel.
The obtained coating solution was coated on a stretched nylon film (Kohjin biaxially stretched polyamide film “Bonyl”, thickness 15 μm) with a Mayer bar and dried. Table 1 shows the coating amount and the film surface temperature during drying. The film surface temperatures when dried at 115 ° C. for 15 seconds and 140 ° C. for 15 seconds were 50 ° C. and 70 ° C., respectively, as heat label temperatures (manufactured by Micron).
The obtained film was returned to room temperature and then aged at 55 ° C. for 96 hours to obtain a gas barrier film of the present invention.
The film was laminated with 50 μm of polyethylene (FC-D; manufactured by Tosero Co., Ltd.) using an adhesive for dry lamination E-370 / C76 (manufactured by Dainichi Seika Co., Ltd.), then immersed in water for at least 24 hours, and 20 ° C. After conditioning with 90% RH, the oxygen gas permeability was measured under the same conditions. The results are shown in Table 1.

Examples 5-8
In Example 1, lactic acid was used as the organic acid, and the same procedure as in Example 1 was carried out except that the amount added was 4.4% by weight.
In addition, the pH of the coating liquid in this example was 3.0 and it was stable for 96 hours or more at room temperature, and it did not gel.

Comparative Example 1
In Example 4, it implemented like Example 4 except the addition amount of glycolic acid having been 27 weight%.

Comparative Example 2
In Example 4, it implemented like Example 4 except the addition amount of glycolic acid having been 0.3 weight%.

Comparative Example 3
In Example 4, it implemented like Example 4 except not having added glycolic acid.

Comparative Example 4
In Example 4, it carried out similarly to Example 4 except having added 4.4 weight% of aluminum sulfate instead of glycolic acid.

Comparative Example 5
In Example 4, it implemented like Example 4 except having added 4.6 weight% of acetic acid instead of glycolic acid.

Comparative Example 6
In Example 4, it implemented like Example 4 except having added 17 weight% of acetic acid instead of glycolic acid.

  From Table 1, an organic acid having a pKa of 4.00 (25 ° C., 0.1 mol / dm 3) or less is 0.5 to 15 weights with respect to a coating solution composed of a mixture of an alkoxysilane hydrolyzate and polyvinyl alcohol. % (Solid content ratio) addition improves the stability of the coating liquid, maintains excellent barrier properties under high humidity even when the gas barrier layer is thinned, and suppresses cracks to provide stable gas barrier properties. It can be seen that can be expressed.

  As described above, according to the present invention, the gas barrier film is excellent in the stability of the coating solution, has little deterioration in the gas barrier property under high humidity even when the gas barrier layer is thinned, and can be stably produced while suppressing cracks. Can be suitably used as a packaging material in various fields such as foods, pharmaceuticals, and precision electronic parts.

Claims (3)

Alkoxysilane and / or alkoxysilane weight represented by the general formula [1] (wherein R represents the same or different alkyl group having 1 to 4 carbon atoms, and n represents an integer of 0 to 10). An organic acid having a pKa of 4.00 (25 ° C., 0.1 mol / dm ³ ) or less is added to a mixture of the hydrolyzate of the condensate and polyvinyl alcohol in an amount of 0.5 to 15% by weight (solid content). Ratio) A gas barrier film in which the added coating solution is coated on at least one side of a base material made of a plastic film.

  The gas barrier film according to claim 1, further comprising an adhesive layer between the plastic film and the coating layer.   The gas barrier film according to claim 1 or 2, wherein the plastic film is a stretched polyamide film.