JP2001138451A - Oxygen gas barrier film and manufacturing method for the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a biaxially oriented polypropylene resin film having high oxygen gas barrier properties at a high humidity by remarkably improving the oxygen gas barrier properties of the biaxially oriented polypropylene resin film at the high humidity by forming the biaxially oriented polypropylene resin film as a base material film, laminating a PVA layer through the adhesive layer, and upgrading crystallinity of a PVA layer. SOLUTION: The oxygen gas barrier film is obtained by laminating a polyvinyl alcohol resin layer having a thickness of 1 μm ore less, the degree of polymerization of 300 to 2,000 and the degree of saponification of 90 to 99.7% on at least one surface of a biaxially oriented polypropylene resin film through an adhesive layer in such a manner that an oxygen permeability in an atmosphere having a relative humidity of 85% is 500 ml/m2.day.MPa or less.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an oxygen gas barrier film and a method for producing the same, and more particularly to an oxygen gas barrier biaxially stretched polypropylene resin film suitable for packaging and further as a food packaging film and a method for producing the same. More specifically, the present invention relates to a film that does not generate hydrogen chloride gas when burned and has excellent oxygen gas barrier properties, particularly excellent oxygen gas barrier properties under high humidity, and a method for producing the same.

[0002]

2. Description of the Related Art Many oxygen gas barrier films and packaging materials using the same have been known. As the most common oxygen gas barrier film, a PVDC coated film coated with a polyvinylidene chloride-based resin (hereinafter sometimes abbreviated as “PVDC”) is well known. The PVDC coated film has almost no hygroscopicity and has good oxygen gas barrier properties even under high humidity.

However, since a film using PVDC generates hydrogen chloride gas by combustion, replacement with an oxygen gas barrier film is strongly desired.
However, at present, a material that is satisfactory as a substitute for PVDC has not yet been obtained due to insufficient oxygen gas barrier properties under high humidity and high cost.

As a material having a high oxygen gas barrier property, a polyvinyl alcohol resin (hereinafter sometimes abbreviated as “PVA”) is well known. PVA-coated films or PVA films show very excellent oxygen gas barrier properties under low humidity, but because of their excellent hygroscopicity, the oxygen gas barrier properties decrease as the relative humidity increases, and it has been considered that the practicality is poor. .

[0005] In order to improve the hygroscopicity of PVA, an ethylene-vinyl alcohol copolymer (hereinafter sometimes abbreviated as "EVOH") is known by copolymerizing it with ethylene. Oxygen gas barrier properties are lower than PVA, and JP-A-3-30944 discloses "PV
A method of adding a swellable colloidal hydrated layered silicate compound to the coating solution A).
Japanese Patent No. 2,789,705 discloses "modified polyvinyl alcohol modified with at least one of a swellable colloidal hydrous phyllosilicate compound and a compound having a silyl group in the molecule". However, all of the films are expensive, and P films exhibiting a high oxygen gas barrier property by coating.
It could not replace VDC coated film.

After coating PVA on the film,
Regarding stretching, JP-A-49-64676 describes lamination with polyethylene terephthalate.
It is stated that the adhesive strength cannot be obtained by applying and stretching the solution A.

[0007]

In view of these circumstances, the present inventors have improved the oxygen gas barrier properties of PVA under high humidity as an alternative to a PVDC-coated biaxially stretched polypropylene resin film, and have achieved an inexpensive method. As a result of intensive studies on packaging materials, the problems of the conventional oxygen-gas-barrier biaxially-stretched polypropylene-based resin film were solved, and the biaxially-stretched polypropylene-based resin film was used as a base film, and a PVA layer was formed via an adhesive layer. Are stacked, and
It has been found that by improving the crystallinity of the PVA layer, the oxygen gas barrier properties of the biaxially oriented polypropylene resin film under high humidity can be greatly improved. An object of the present invention is to provide a biaxially oriented polypropylene-based resin film having high oxygen gas barrier properties under high humidity, which could not be obtained with a resin film, and a method for producing the same.

[0008]

In order to achieve the above object, the oxygen gas barrier film of the present invention has a thickness of 1 μm or less via an adhesive layer on at least one surface of a biaxially stretched polypropylene resin film. And a degree of polymerization of 30
0 to 2000, a polyvinyl alcohol resin layer having a saponification degree of 90 to 99.7%, and a relative humidity of 8
Oxygen permeability under a 5% atmosphere is 500 ml /
m ² · day · MPa or less.

The oxygen gas barrier film of the present invention having the above constitution is a biaxially oriented polypropylene having a high oxygen gas barrier property under high humidity, which cannot be obtained with a conventional PVA-coated biaxially oriented polypropylene resin film. It is a base resin film.

[0010] In this case, polyvinyl ratio of absorbance of alcohol 1140cm resin layer to the absorbance of the infrared absorption spectrum of 1090cm ^{-1 -1} (D1140 / D
1090) can be a film exhibiting 0.7 or more.

In this case, the adhesive layer can be made of an acid-modified polyolefin.

Further, the method for producing an oxygen gas barrier film of the present invention is characterized in that the unstretched film having an adhesive layer laminated on at least one surface of a polypropylene resin film is stretched in one direction, and then the adhesive layer Is characterized in that a polyvinyl alcohol-based resin layer is formed on the surface thereof, and then the film is stretched in a direction perpendicular to the stretching direction.

According to the method for producing an oxygen gas barrier film of the present invention having the above constitution, the obtained biaxially oriented polypropylene-based resin film and polyvinyl alcohol-based resin layer have strong adhesion and are excellent under high humidity. Shows oxygen gas barrier properties.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the oxygen gas barrier film and the method for producing the same according to the present invention will be described.

The biaxially stretched polypropylene resin film used in the present invention is formed from a polypropylene resin homopolymer, a random copolymer with a small amount of ethylene, butene, pentene, hexene or the like, a block copolymer or the like. Or a mixture of two or more polymers. Further, if necessary, it may contain a moisture-proof property improving resin such as a petroleum resin or a terpene resin.

The thickness of the biaxially stretched polypropylene resin film is not particularly limited, but is usually 10 to 250 μm.
It is particularly preferable that the packaging material has a thickness of 15 to 60 μm. The biaxially stretched polypropylene resin film as the base film may be a single film or a composite multilayer film, and the composite method and the number of layers in the multilayer film are arbitrary.

The degree of polymerization and the degree of saponification of the PVA used in the present invention are determined from the properties of the target film, particularly the oxygen gas barrier property, the viscosity of the PVA aqueous solution at the time of film production, and the stretchability of the film after coating. Regarding the stretchability, the higher the degree of polymerization, the slower the crystallization speed and the better the stretchability. However, if the degree of polymerization is too high, the viscosity of the aqueous solution becomes too high, and coating becomes difficult. Therefore, the degree of polymerization is 300 or more from the viewpoint of the stretchability of the coating film, and is 2000 or less from the viewpoint of coating suitability, and preferably 500 to 1700. About saponification degree, 9
If it is less than 0%, the target oxygen gas barrier property cannot be obtained under high humidity, and if it exceeds 99.7%, it is difficult to adjust the aqueous solution and it tends to gel, which is not suitable for industrial production. Therefore, the degree of saponification is 9
0-99.7% is preferable.

The infrared absorption spectrum of the PVA layer
By the ratio of absorbance at 1140 cm ^-1 to the absorbance of cm ^-1 (D1140 / D1090) is 0.7 or more, the oxygen gas barrier properties at high humidity of PVA layer is improved, further comparison with the conventional method Then, a thin film having excellent oxygen gas barrier properties can be obtained. This is achieved by stretching a laminated film of a polypropylene-based resin film layer and an adhesive layer in a uniaxial direction, laminating a PVA aqueous solution on the adhesive layer, and then stretching the film at right angles to the stretching direction. 1140 cm ^-1 is the wavelength at which absorption of the crystalline band of PVA is recognized, and 1090 cm ^-1
-1 is a wavelength at which absorption based on the stretching motion of C-O appears. According to this method, the degree of crystallinity can be easily evaluated. It is considered that the higher the crystallinity, the higher the oxygen gas barrier property.

In the method for producing the oxygen gas barrier film of the present invention, it is preferable to laminate an adhesive layer at the time of forming a polypropylene resin film as a base layer. A particularly preferred method is to laminate both layers by a coextrusion method. Such a laminated film is uniaxially stretched, and thereafter, a PVA layer is laminated on the adhesive layer, and then stretched in a direction perpendicular to the stretching direction.

The adhesive layer may be any as long as it bonds the PVA layer and the polypropylene resin film layer, and it is preferable to use an acid-modified polyolefin, and the acid-modified polyolefin is not particularly limited. Generally, any graft copolymer containing 0.01 to 5 mol% of maleic acid or maleic anhydride units obtained by graft copolymerizing maleic acid or maleic anhydride with an olefin polymer may be used.

As a method of laminating PVA, a coating method is particularly preferred. The coating method is not limited, but an optimum method may be selected depending on the application amount and the viscosity of the PVA aqueous solution to be used. A reverse roll coating method, a roll knife coating method, a die coating method, or the like may be employed.

The conditions of drying and heat treatment at the time of coating depend on the thickness of the coating and the conditions of the apparatus, but the film is immediately sent to the stretching step in the perpendicular direction without providing a drying step, and depends on the preheating zone of the stretching step or the conditions during stretching. Drying is preferred. If necessary, it is usually carried out at about 80 to 170 ° C. If necessary, before forming the PVA layer, the polypropylene resin film may be subjected to a corona discharge treatment or other surface activation treatment or an anchor treatment using a known anchor treatment material. The addition of various known inorganic and organic additives such as an antistatic agent, a slipping agent, and an antiblocking agent to the PVA layer is optional as long as the object of the present invention is not impaired.

The thickness of the PVA layer varies depending on the polypropylene resin film and the target level.
The minimum thickness for exhibiting the oxygen gas barrier performance is good, and it is usually preferable that the dry thickness is 1 μm or less in terms of transparency, handleability, economy and the like.

Next, a heat-sealable resin layer is formed on the PVA layer after stretching, if necessary. The formation of the heat-sealable resin layer is usually performed by an extrusion lamination method or a dry lamination method.

The thermoplastic polymer forming the heat-sealing resin layer used in the present invention includes HDPE, LDP
E, polyethylene resin such as LLDPE, PP resin,
What is usually used as a heat seal resin, such as an ethylene-vinyl acetate copolymer, an ethylene / α-olefin random copolymer, and an ionomer resin, can be used as it is. As the heat seal resin, a resin other than a chlorine-containing resin is selected from the viewpoint of environmental problems during incineration treatment after use.

According to the present invention, the oxygen gas barrier property which is inexpensive, has excellent oxygen gas barrier properties, does not contain hydrogen chloride gas in the combustion exhaust gas, is effective for environmental protection which has recently become a problem, and is excellent under high humidity Can be provided.

[0027]

Next, the present invention will be described in detail with reference to the following examples and comparative examples, but the present invention is not limited to these examples. Unless otherwise specified, the density display in the examples is based on weight, and the evaluation of characteristic values in the specification was performed according to the following method.

1. Oxygen permeability Oxygen permeability is "MOCON" manufactured by Modern Control.
Using "OX-TRAN 2/20", the measurement time was 30 minutes in an atmosphere controlled at 23 ° C. and 65% and 85% relative humidity. The unit of the oxygen permeability was expressed in milliliter / m ² · day · MPa.

2. Haze Based on ASTM-D-1003-61.

3. Absorbance ratio The absorbance ratio of the infrared absorption spectrum is JIS-K-0117.
It measured based on.

(Examples 1 to 5 and Comparative Examples 2 to 3) PVA
Used were those having the degree of polymerization and the degree of saponification shown in Table 1. The above-mentioned PVA was gradually added to an aqueous solution containing 7% of isopropyl alcohol while stirring, and after uniformly dispersing, the container was sealed. After heating to about 80 ° C to completely melt, keep at 40 ° C for PVA 5, 10, and 1
A 5% by weight aqueous solution was prepared.

As a base layer, 97% by weight of a polypropylene resin is mixed with 3% by weight of a petroleum resin (Escolets E5300: manufactured by Tonex Corporation) substantially free of a polar group, and an acid-modified polyolefin is used as an adhesive layer. Co-extrusion from a T-die in a two-layer state so that the resin temperature becomes 260 ° C. at a ratio of layer = 19/1 (weight ratio).
After casting with a 5 ° C. casting roll, the film was stretched 4 times in the machine direction. After coating each of the PVA aqueous solution on the adhesive layer surface of the obtained laminated film by a reverse roll coating method, the film is stretched 9 times in the lateral direction,
A laminated film was obtained.

Comparative Example 1 PVA having a polymerization degree and a saponification degree shown in Table 1 was used. An isocyanate-based adhesive was applied as a anchor to the surface of the biaxially stretched polypropylene-based resin film having a thickness of 20 μm, which had been subjected to corona discharge treatment, and gravure-coated so that the coating amount was 0.3 g / m ² after drying. PVA was similarly gravure coated on the anchor layer, the drying temperature was 140 ° C., and a laminated film was obtained.

Comparative Example 4 According to Example 1, but without laminating the adhesive layer on the base layer, PVA was directly applied to a film only on the base layer.
Except for laminating the layers, an attempt was made to produce a laminated film by the same method as in Example 1. However, the PVA layer was stuck and peeled off on the press roll side during film winding, and a practical laminated film could not be obtained. Was.

With respect to each of the laminated films of Examples 1 to 5 and Comparative Examples 1 and 2, the absorbance ratio of the infrared absorption spectrum and the oxygen permeability at a relative humidity of 65% and 85% were measured. Indicated.

As shown in Table 1, the oxygen gas barrier film of the present invention has improved crystallinity as compared with the conventional PVA-coated film, and therefore has excellent oxygen gas barrier properties under high humidity, and It has been clarified that the same oxygen gas barrier property under low humidity can be obtained even though it is a thin film as compared with the PVA coat film of No.

[0037]

[Table 1]

Further, according to the present invention, the conventional P
Compared to the method of manufacturing a VA coated film, PVA is used at once in the process of manufacturing a biaxially stretched polypropylene resin film.
This is extremely practical.

[0039]

According to the oxygen gas barrier film and the method for producing the same of the present invention, a biaxially stretched polypropylene resin film coated with PVA is inexpensive and has a high oxygen gas barrier property under high humidity. In addition, the method of the present invention for producing a film in which PVA is coated on a biaxially oriented polypropylene-based resin film can be performed under a high humidity condition. However, excellent high oxygen gas barrier properties can be provided.

 ──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Katsushi Yamamoto 344 Maebata, Mazuhata, Kizu, Inuyama-shi, Aichi Prefecture Inside the Inuyama Plant of Toyobo Co., Ltd. Inside the Inuyama Plant of Toyobo Co., Ltd. CB00 EC182 EH461 EJ371 EJ372 EJ38A GB15 JA07B JA07C JA20B JA20C JB20B JB20C JD03 JN30B JN30C YY00 YY00B YY00C

Claims (4)

[Claims] 1. A film having a thickness of 1 μm on at least one surface of a biaxially stretched polypropylene resin film via an adhesive layer.
The following, polymerization degree 300-2000, saponification degree 90-
An oxygen gas barrier comprising a 99.7% polyvinyl alcohol-based resin layer laminated thereon and having an oxygen permeability of 500 ml / m ² · day · MPa or less under an atmosphere of a relative humidity of 85%. Film. 2. An infrared absorption spectrum of the polyvinyl alcohol-based resin layer of 114 to an absorbance of 1090 cm ^−1.
The absorbance ratio of 0 cm ^-1 (D1140 / D1090) is
2. The oxygen gas barrier film according to claim 1, wherein the thickness is 0.7 or more. 3. The oxygen gas barrier film according to claim 1, wherein the adhesive layer comprises an acid-modified polyolefin. 4. An unstretched film having an adhesive layer laminated on at least one surface of a polypropylene-based resin film is stretched in one direction, and thereafter, a polyvinyl alcohol-based resin layer is formed on the surface of the adhesive layer. 4. The method for producing an oxygen gas barrier film according to claim 1, wherein the film is stretched in a direction perpendicular to the stretching direction.