JPH10152527A - Polyvinyl alcohol-based polymer, packing material and composition for coating - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a polyvinyl alcohol-based polymer capable of maintaining gas barrier properties even in high humidity by introducing a specific group into the main chain of the polymer. SOLUTION: The objective polymer is obtained by hydrating a copolymer of a compound of formula I(R1 is H, CH3 , C2 H5 , etc.; R2 is H, CH3 , C2 H5 , etc.; R3 is CH3 , C2 H5 etc.), (e.g. isopropenyl acetate and 2-propenyl acetate) and a compound of formula II (R4 is CH3 , C2 H5 , etc.), (e.g. vinyl acetate) under a basic condition (e.g. in an aqueous solution of sodium hydroxide). The polymer is completely saponified and the sapondification degree is >=99.8%. A packing material is obtained by laminating the polymer on a substrate film by performing a melt extrusion or by coating the polymer dissolved in methyl alcohol, etc., on the substrate film, or on a fibrous substrate, or by dipping the fibrous substrate into the polymer dissolved in methyl alcohol, etc.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polymer which provides a layer having excellent gas barrier properties, and more particularly to a polymer suitable for obtaining a packaging material having excellent gas barrier properties. More specifically, the present invention relates to an invention for obtaining a layer having improved water resistance while maintaining high gas barrier properties when obtaining a layer having excellent gas barrier properties using a polyvinyl alcohol-based polymer.

[0002]

2. Description of the Related Art Conventionally, packaging materials for packaging foods and various articles often require gas barrier properties, particularly oxygen barrier properties. This is to prevent the package contents from being oxidized and degraded by oxygen or the like.
Particularly in the packaging of foods, there is a problem in that the presence of oxygen causes microorganisms to propagate and the contents to spoil. For this reason, a conventional packaging material is provided with a gas barrier layer for preventing the permeation of oxygen, thereby preventing permeation of oxygen and the like.

[0003] The gas barrier layer is generally a metal foil or a vapor-deposited layer of a metal or a metal compound, and an aluminum foil, an aluminum vapor-deposited layer, a silicon oxide vapor-deposited layer, and the like are practical. On the other hand, among general plastic films used as packaging materials, resins having excellent gas barrier properties, such as polyvinyl alcohol-based polymers and polyvinylidene chloride, are sometimes used.

However, those using the above metals are
There is a problem that the contents cannot be seen, and there is a demerit that the disposability is poor. On the other hand, gas barrier plastics were transparent and had little problem of disposal. Taking advantage of these advantages, polyvinyl alcohol polymers are widely used as gas barrier polymers.

[0005]

However, the above-mentioned polyvinyl alcohol-based polymer is crystallized by a hydrogen bond between the hydroxyl groups of the polymer to exhibit a gas barrier property. It is known that, while exhibiting gas barrier properties, in a state where the polymer has absorbed moisture due to water vapor in the atmosphere, the above-described hydrogen bonds are loosened and the gas barrier properties are reduced.

[0006] By copolymerizing ethylene with polyvinyl alcohol, water resistance can be slightly improved, but there is a limit. It is also possible to improve water resistance by denaturing and crosslinking the polyvinyl alcohol-based polymer, but this time, a void is formed in the cross-linked polyvinyl alcohol-based polymer, and this void serves as a path for oxygen. As a result, there is a problem that the gas barrier property is reduced. Thus, it has been difficult to satisfy both the gas barrier property and the water resistance of the polyvinyl alcohol-based polymer.

The present inventor has solved the above-mentioned conventional problems by solving a polymer of a compound represented by the following formula [1] or a compound represented by the following formula [1] and a compound represented by the following formula [2]: The position of the hydroxyl group is regulated by introducing a methyl group or an ethyl group into the main chain of the polymer, and the polymer obtained by hydrolyzing these terpolymers is crystallized by hydrogen bonding. It has been found that the gas barrier property can be maintained even under high humidity, and the present invention has been completed.

[0008]

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[0009]

That is, a first invention of the present invention is a polyvinyl alcohol-based polymer obtained by hydrolyzing a polymer of a compound represented by the following formula [1].

[0010]

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Further, the second invention of the present invention provides the following formula [1]
Is a polyvinyl alcohol-based polymer obtained by hydrolyzing a copolymer of a compound represented by the following formula and a compound represented by the following formula [2].

[0012]

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[0013] A third invention of the present invention is a packaging material having, on a base film, a layer formed by melt-extruding the polyvinyl alcohol-based polymer of the first invention or the second invention.

[0014] A fourth invention of the present invention is a coating composition in which the polyvinyl alcohol-based polymer of the first invention or the second invention is dissolved in a solvent.

A fifth aspect of the present invention is a packaging material having a coating layer formed by applying and drying the coating composition of the fourth aspect on a base film.

According to a sixth aspect of the present invention, there is provided a packaging material comprising a fibrous base material coated or impregnated with the coating composition of the fourth aspect.

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION The polyvinyl alcohol polymer of the present invention is a polymer of a single compound represented by the following formula [1] or a compound represented by the following formula [1] and a compound represented by the following formula [2]: It is a copolymer with the compound represented and a polymer obtained by hydrolyzing these terpolymers. Compounds represented by the following formula [1] include isopropenyl acetate, acetic acid 2
Examples of the compound represented by the following formula [2] such as -propenyl and the like include vinyl acetate and the like.

[0018]

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A polymer of a compound represented by the following formula [1]:
Alternatively, a compound represented by the following formula [1] and a compound represented by the following formula [2]
In order to obtain a copolymer with the compound represented by the formula (1) and terpolymers thereof, they can be produced by polymerizing these with a polymerization initiator. The ratio of the compound represented by the following formula [1] is 1 to all monomers to be polymerized.
It must be 0 mol% or more. If the amount is less than this, the number of methyl groups in the main chain in the final target product decreases, so that the crystallinity does not increase and the desired gas barrier property cannot be obtained.

[0020]

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As the polymerization initiator, α, α'-azobisisobutyronitrile (AIBN), azobisisovaleronitrile, azobis (4-methoxy-2,4-dimethylvaleronitrile), azobis (2,4-dimethyl Valeronitrile), benzoyl peroxide (BPO), di-tert-butyl peroxide, etc., which initiate polymerization by heat can be used. The polymerization initiator is used in an amount of 0.01 to
What is necessary is just to add about 10 weight%. The reaction temperature is 40 to 1
6 to 72 at 40 ° C, preferably 60 to 100 ° C.
The reaction is carried out for a period of time, preferably 12 to 24 hours.

The desired polymer is obtained by hydrolyzing the produced polymer under basic conditions. For the hydrolysis, an aqueous solution of an alkaline substance such as sodium hydroxide, potassium hydroxide, ethylenediamine, diethylenetriamine or the like can be used. This polymer can be completely saponified and has a degree of saponification of 99.8% or more. The copolymer obtained by copolymerization is a random copolymer.

The polymer of the present invention obtained as described above has a film forming property (film forming property) of about 5,000.
It preferably has the above molecular weight. Since this polymer has thermoplasticity, various additives (for example, sodium alkyl sulfate or fluorine-based surfactant for preventing repelling) are added and mixed as it is or as necessary. Thereby, it can be melt-extruded and laminated on a base film such as a plastic film. Also, by dissolving in a mixed solvent of alcohol such as methyl alcohol or ethyl alcohol and dimethylformamide, dimethylacetamide, dimethylsulfoxide, N-methylmorpholine oxide, etc., as it is, or if necessary, various additives are added, By mixing, it can be used as a coating composition for a base film such as a plastic film, or a coating or impregnating composition for a fibrous base material such as paper, nonwoven fabric, or synthetic paper.

[0024] Lamination by melt extrusion to a base film and use by coating are one of the effective uses of the present invention. That is, by applying a lamination or coating composition by melt extrusion to a base film, heating and drying to form a coating comprising the composition of the present invention, a gas barrier property can be imparted to the base film, and This is because a packaging material having excellent barrier properties can be obtained.

The substrate film is not particularly limited as long as it can be coated with a lamination or coating composition by melt extrusion.
Normal packaging materials such as polypropylene), polyesters (polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, etc.), polyamides (nylon-6, nylon-66, etc.), polyvinyl chloride, polyimide, etc., and copolymers of these polymers Can be used. Of course, a multilayer film obtained by laminating a plurality of these can also be used. Among these base films, biaxially stretched polyethylene terephthalate film,
An axially stretched polypropylene film, a biaxially stretched nylon film, a film having a thickness of about 12 to 100 μm, or a multilayer film containing these films is suitably used.

If necessary, a paper layer or the like may be added to the above film for the purpose of decoration or the like.

As a method of forming a layer by melt extrusion, there is a method of extruding a single layer and laminating the substrate film by a dry laminating method or the like, or a method of laminating the substrate film by coextrusion. As a method for coating the base material film with the coating composition, conventionally known means such as a casting method, a dipping method, a roll coating method, a screen printing method, and a spraying method are used. The thickness of the coating may be such that the thickness after drying is in the range of about 0.01 to 100 μm. Similarly, coating on fibrous base material /
Impregnation can also be performed by a well-known method.

The packaging material of the present invention obtained as described above is heat-sealed into a shape such as a well-known three-side seal bag, four-side seal bag, gusset-like bag, standing pouch, or pillow packaging bag, for example. It can be used after making a bag.

[0029]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail with reference to embodiments.

Example 1 Isopropenyl acetate (10.0 g) and vinyl acetate (2.2 g) were placed in a polymerization tube, and AIBN (1.0 g) was added. The vacuum and nitrogen replacement are repeated under freezing, and the tube is sealed under reduced pressure. Thereafter, a radical polymerization reaction is performed at 60 ° C. for 24 hours. After the reaction is completed, the polymer is dissolved in benzene and reprecipitated from a large amount of n-hexane. The precipitate is collected, washed with n-hexane, and dried under reduced pressure. Next, this polymer was dissolved in acetone, and 2N-NaO
Hydrolysis is carried out with an aqueous H solution. The resulting precipitate is repeatedly subjected to Soxhlet extraction with methanol to obtain the desired product (molecular weight: about 25,000, degree of saponification: 99.8% or more).

Example 2 Isopropenyl acetate (10,
0g) with 2-propenyl acetate (10.0 g), AIBN
Polymerization was carried out in the same manner as in Example 1 except that (1.0 g) was changed to BPO (0.5 g) (molecular weight: about 22,000).
0, degree of saponification: 99.8% or more).

<Example 3> Vinyl acetate (4.
3 g), isopropenyl acetate (5.0 g), 2-propenyl acetate (5.0 g) and AIBN (1.0 g).
g) is added. Reduce the pressure under freezing, repeat nitrogen replacement,
Seal under reduced pressure. Thereafter, a radical polymerization reaction was performed at 80 ° C. for 24 hours. After the reaction was completed, the polymer was dissolved in benzene,
Reprecipitation is performed from a large amount of n-hexane. Collect the precipitate
-Wash with hexane and dry under reduced pressure. Next, the polymer is dissolved in acetone and hydrolyzed with a 2N-NaOH aqueous solution. The resulting precipitate is repeatedly subjected to Soxhlet extraction with methanol to obtain the desired product (molecular weight: about 12,000,
(Saponification degree: 99.8% or more, saponification degree: 99.8% or more).

Example 4 Isopropenyl acetate (10.0 g) was placed in a polymerization tube, and then di-tert-butyl peroxide (500 mg) was added. The vacuum and nitrogen replacement are repeated under freezing, and the tube is sealed under reduced pressure. Thereafter, a radical polymerization reaction is performed at 100 ° C. for 24 hours. After the reaction is completed, the polymer is dissolved in benzene and reprecipitated from a large amount of petroleum ether. The precipitate is collected, washed with n-hexane, and dried under reduced pressure. Next, this polymer was dissolved in acetone, and 2N-NaO
Hydrolysis is carried out with an aqueous H solution. The resulting precipitate is repeatedly subjected to Soxhlet extraction with methanol to obtain the desired product (molecular weight: about 5,500, saponification degree: 99.8% or more).

Example 5 2-Propenyl acetate (10.0 g) was placed in a polymerization tube, and then azobisisovaleronitrile (500 mg) was added. The vacuum and nitrogen replacement are repeated under freezing, and the tube is sealed under reduced pressure. Then at 40 ° C for 48
A radical polymerization reaction is carried out for a time, and after the reaction is completed, the polymer is dissolved in benzene, and reprecipitated from a large amount of n-hexane.
The precipitate is collected, washed with n-hexane, and dried under reduced pressure. Next, this polymer was dissolved in acetone, and 2N-NaOH was used.
Hydrolysis is carried out with an aqueous solution. The resulting precipitate is repeatedly subjected to Soxhlet extraction with methanol to obtain the desired product (molecular weight:
About 7,000, degree of saponification: 99.8% or more).

Each of the copolymers obtained in Examples 1 to 5 was dissolved in DMSO, and the resulting solution was cast on a Teflon plate to form a film (thickness: 20 μm). After heating and drying, the film was peeled off to obtain a sample for measuring the oxygen gas barrier property. For comparison, as Comparative Example 1, commercially available polyvinyl alcohol was formed into a film (thickness: 2).
0μ, molecular weight: about 75,000, degree of saponification: 99.8
%) (Manufactured by Kuraray Co., Ltd.). Table 1 shows the results. The numerical value is the oxygen permeability. Measurement of oxygen permeability
MOCON OX-TRAN made by Modern Control
Using the Mocon method. (Oxygen permeability unit: CC / m ² · day · atm)

[0036]

[Table 1]

As can be seen from the above results, the composition of the present invention maintains low oxygen permeability (high gas barrier property) even in a high humidity atmosphere.

[0038]

As described above, in the polyvinyl alcohol-based polymer according to the present invention, the position of the hydroxyl group is regulated by introducing a methyl group into the main chain of the polymer, and the crystallinity is increased by the hydrogen bond. High oxygen gas barrier properties can be obtained even under high humidity.

Claims (6)

[Claims] 1. A polyvinyl alcohol-based polymer obtained by hydrolyzing a polymer of a compound represented by the following formula [1]. Embedded image 2. A polyvinyl alcohol-based polymer obtained by hydrolyzing a copolymer of a compound represented by the following formula [1] and a compound represented by the following formula [2]. Embedded image 3. A packaging material comprising, on a base film, a layer formed by melt-extruding the polyvinyl alcohol-based polymer according to claim 1 or 2. 4. A coating composition wherein the polyvinyl alcohol-based polymer according to claim 1 or 2 is dissolved in a solvent. 5. A packaging material having a coating layer formed by applying and drying the coating composition according to claim 4 on a substrate film. 6. A fibrous base material, wherein the coating composition according to claim 4 is applied or impregnated.
Packaging material.