JPH0688367B2 - Film for packaging - Google Patents

Description

TECHNICAL FIELD The present invention relates to a film for packaging foods, medicines, etc. More specifically, it has a high degree of water vapor barrier property and excellent transparency. It relates to a packaging film.

(Prior Art) Conventionally, a plastic film, which is excellent in flexibility, transparency, processability, durability and low in cost, has been widely used as a packaging material for food or medicine. In the fields of food packaging and chemical packaging, it is essential that the materials used for packaging have excellent water vapor barrier properties in order to protect the contents from decay and deterioration and to enable long-term storage.

However, the water vapor barrier property of the plastic film is not sufficient for the above purpose at present, and various methods have been used to impart the water vapor barrier property to the plastic film. This method includes a method of coating a resin having a high water vapor barrier property such as polyvinylidene chloride, polyvinyl alcohol, etc., laminating a metal such as aluminum foil, or vapor deposition of a metal such as aluminum.

The resin coating requires a considerable thickness to provide a water vapor barrier property, but the expected water vapor barrier property cannot be obtained for the thickness. Also, aluminum foil lamination and metal vapor deposition are relatively excellent in water vapor barrier properties, but the state of the contents inside the package cannot be known from the outside because the metal layer blocks light rays, so it is a packaging material. It has the drawback of being considered fatal.

The present inventors have previously formed a zinc sulfide thin film layer on a film in order to solve the above problems and obtain a packaging film having a high degree of water vapor barrier property and excellent transparency. Proposed packaging film (Japanese Patent Application No. 61-62045)
issue).

(Problems to be Solved by the Invention) The method previously proposed by the inventors of the present invention as described above has a high degree of water vapor barrier property and is excellent in transparency. It was found that there is a problem because the layer is a single layer film. Once a pinhole is generated during film formation, the generated pinhole directly becomes a defect in the thin film layer and finally remains, so that a high barrier property cannot be achieved. Further, even if the film thickness is increased, there is a limit to the barrier property that can be achieved, and rather, the adverse effects of increasing the film thickness, such as easy occurrence of cracks, become greater. Further, even when the single-layer film is formed twice or more, pinholes are likely to occur in the film formed next at the same place as the pinhole existing in the film formed first.

It is an object of the present invention to solve the above-mentioned drawbacks of the prior art and to provide a packaging film which is transparent and has a higher water vapor barrier property than ever before.

(Means for Solving Problems) As a result of earnest research to solve such problems, the present inventors formed a zinc sulfide thin film layer on a plastic film and then formed a transparent resin layer. Then, the inventors have found that by forming a zinc sulfide thin film layer on it again, it is possible to obtain a more excellent water vapor barrier property than before without impairing transparency, and arrived at the present invention.

That is, the present invention provides a barrier layer in which a zinc sulfide thin film layer, a transparent resin layer, and a zinc sulfide thin film layer are sequentially laminated on at least one surface of a transparent plastic film, and the film thickness of one layer of the zinc sulfide thin film layer of this barrier layer is provided. Is 0.02 to 1.0 μm, and the film thickness of the transparent resin layer is 0.5 μm or more, and a packaging film is provided.

The plastic film used in the present invention is transparent,
What is normally used for packaging may be used. Examples include, but are not limited to, films of nylon, polyester, polypropylene, polyvinyl alcohol, polyvinyl chloride, polyethylene, polystyrene, polyimide, polycarbonate, polyarylate, polyethylene vinyl alcohol copolymer, and the like. Absent.
These films may be used alone or laminated. If necessary, these films may be subjected to surface treatment such as corona discharge treatment or plasma treatment, or may be coated with an anchoring agent such as alkyl titanate, polyethyleneimine or isocyanate on the film, or polychlorinated. It may be coated with a resin having a barrier property such as vinylidene. However, if the surface roughness is too large or if wrinkles are present, it is difficult to form a uniform and continuous zinc sulfide thin film layer on the film, which is not preferable.

The zinc sulfide thin film layer can be formed by a vacuum thin film forming method generally called physical vapor deposition method, that is, a vacuum vapor deposition method, an ion plating method, a sputtering method or the like. The ion plating method is preferable in terms of the adhesion strength of the thin film and the film formation rate, but is not particularly limited.

The thickness of the zinc sulfide thin film layer is 0.02 to 1.0 μm for the single layer. When the film thickness is 0.02 μm or less, the thin film does not become a uniform continuous film, and the effect expected by the present invention cannot be obtained. If the film thickness is 0.02 μm or more, the effect of the present invention appears, but more preferably, the film thickness is 0.04 μm or more. On the other hand, if the film thickness exceeds 1.0 μm, the barrier property is not improved in spite of the increase in the film thickness, and in some cases, cracking is likely to occur.

As the resin used for the transparent resin layer, polyester,
Polycarbonate, polymethylmethacrylate, polyurethane, polyvinylidene chloride, polyvinyl alcohol,
Examples thereof include polyamide, polyimide, and epoxy resin, but the transparent material is not limited to this example. As a method for forming the transparent resin layer, a coating method using a known coating machine such as a gravure roll coater, a doctor knife, a bar coater, a curtain coater, a knife coater, a spray method, and a dipping method are used.

The thickness of the transparent resin layer is preferably 0.5 μm or more. 0.5 μm
In the following cases, it is difficult to form a uniform and continuous film, and the effect of providing the resin layer is not sufficiently exerted. Since the usual packaging film has a thickness of 12 μm and 25 μm, the thickness of the practical transparent resin layer, which is well balanced with the thickness of the base film, is preferably 5 μm or less.

It is not clear why a high degree of water vapor barrier property can be obtained by providing a zinc sulfide thin film layer with a transparent resin layer sandwiched between them, but even if defects such as pinholes occur in the first layer of zinc sulfide thin film, it is transparent. The resin layer hides the defect,
This is considered to prevent defects from occurring at the same place when the zinc sulfide thin film layer of the layer grows. Therefore, by forming the transparent resin layer, it is possible to prevent the pinholes of the two zinc sulfide thin film layers from directly overlapping, and as a result, a high degree of water vapor barrier property can be achieved.

When a zinc sulfide thin film layer is formed with a transparent resin layer sandwiched between the transparent resin layer and the zinc sulfide thin film layer, the effect is superior to that of a single layer of zinc sulfide thin film having the same thickness as the total thickness of the zinc sulfide thin film layers.

Normally, it is desirable to apply a transparent resin protective coating on the outer zinc sulfide thin film layer in order to protect the thin film layer. Examples of the transparent resin include acrylic ester resins such as polymethylmethacrylate, acrylic resins such as polyacrylonitrile and polymethacrylonitrile, polyolefin resins such as polyethylene and polypropylene, and silicon resins such as polymers obtained from ethyl silicate. A polyester resin, a melamine resin, a fluorine resin, or the like may be used for coating by a conventionally known method.

If necessary, lamination of zinc sulfide and transparent resin may be repeated.

(Examples) Hereinafter, the present invention will be specifically described with reference to Examples.

In the following examples, each measurement was performed by the following measuring method.

The moisture permeability was measured according to JIS Z 0208 under the conditions of 40 ° C and 90% RH.

The light transmittance was measured by using a spectrophotometer U-3400 (manufactured by Hitachi, Ltd.), and the light transmittance desired to include the substrate at a wavelength of 550 nm was measured using air as a reference.

The film thickness of the zinc sulfide thin film layer is CRM-1D
(Manufactured by Nippon Vacuum Co., Ltd.). However, the crystal oscillator film thickness meter is based on the multiple reflection interferometry method in advance.
It was calibrated using a -9150 Nanoscope (Nichiden Anelva).

Example 1 A 0.06 μm thick zinc sulfide thin film was formed on a 12 μm thick polyethylene terephthalate (PET) film as a substrate, and then a 2 μm thick polyester resin (UE-3050,
The unitika) layer was formed by the barcode method. further,
Zinc sulfide thin film layers having various thicknesses were formed on the resin layer.
Zinc sulfide thin films were formed by RF ion plating method. After evacuating the vacuum system to 1 × 10 ^-5 Torr, introducing argon gas at 2 × 10 ^-4 Torr, voltage 2 kV, frequency 13.5.
Applying a high frequency electric field of 6 MHz at 50 W, the zinc sulfide sinter was heated and evaporated by an electron gun while generating plasma.
It was formed at a deposition rate of Å / s.

The water vapor transmission rate and light transmittance of these samples were measured. The results are shown in Table 1. The total zinc sulfide film thickness is the sum of the film thickness of the first zinc sulfide thin film layer of 0.06 μm and the film thickness of the zinc sulfide thin film layer formed on the resin layer.

From this, it is understood that the water vapor transmission rate becomes small when the film thickness of the zinc sulfide thin film layer is 0.02 μm or more. Further, when the film thickness of the zinc sulfide thin film layer exceeds 1.0 μm, the water vapor transmission rate does not decrease in spite of the increase in film thickness, so the film thickness is preferably 1.0 μm or less.

In addition, zinc sulfide thin films of various thicknesses were formed on PET film, and then 2 μm thick polyester resin (UE-3050,
The same result was obtained when the unitika) layer was formed and finally a 0.06 μm thick zinc sulfide thin film layer was formed. Also,
Good results were obtained when both zinc sulfide thin film layers were formed to 0.02 μm, but the thickness of one of them was 0.02 μm.
When it is less than m, the water vapor transmission rate becomes 1 g / m ² · 24 h or more, and the high-level water vapor barrier property aimed at by the present invention cannot be achieved. From these results, a single layer of zinc sulfide thin film is 0.02
It must be at least μm.

Comparative Example A 0.12 μm-thick zinc sulfide single-layer film was formed on one side of a 12 μm-thick PET film, and then a polyester resin (UE
-3050, Unitika) was applied to a thickness of 2 μm (Comparative Example 1).

In addition, the thickness of 0.06μ on one side of the PET film of thickness 12μm
A zinc sulfide thin film having a thickness of 0.12 μm was obtained by forming a zinc sulfide thin film having a thickness of 0.12 μm without forming a resin layer. Polyester resin (UE-3050, Unitika) with a thickness of 2
It was applied to a thickness of μm (Comparative Example 2).

In addition, 0.06μ thick on both sides of 12μm thick PET film
m zinc sulfide single layer film is formed, and polyester resin (UE-3050, Unitika) is formed on one zinc sulfide thin film to a thickness of 2
It was applied to a thickness of μm (Comparative Example 3).

The zinc sulfide thin film layer was formed by the same RF ion plating method as in Example 1, and the resin was applied by the bar coat method. In all of these comparative examples, the total thickness of the zinc sulfide thin film is 0.12 μm.

The water vapor transmission rate and light transmittance of these samples were measured.
The results are shown in Table 2. Comparing this result with the case where the total zinc sulfide thin film total film thickness of Example 1 is 0.12 μm,
It can be seen that although the zinc sulfide thin film layer has the same film thickness, the comparative example has a higher water vapor transmission rate and a poorer water vapor barrier property.

Example 2 A 0.06 μm-thick zinc sulfide thin film was formed on a 12 μm-thick PET film, a polyester resin (UE-3050, Unitika) was coated to various film thicknesses, and further a 0.06 μm-thickness was applied onto the resin. A zinc sulfide thin film layer of μm was formed. The method of forming each film is the same as that in the first embodiment.

The water vapor transmission rate and light transmittance of these samples were measured.
The results are shown in Table 3. From this result, the thickness of the resin layer is 0.
It can be seen that the water vapor permeability is particularly small when the thickness is 5 μm or more.

Example 3 A 0.06 μm thick zinc sulfide thin film layer was formed on a 12 μm thick PET film, and then a 2 μm thick transparent resin layer was formed. As the resin, polymethylmethacrylate (P 13
30, Dainippon Ink), Polycarbonate (S 200F, Mitsubishi Gas Chemical), Polyurethane (Crisbon NT-150, Dainippon Ink), Polyarylate (U Polymer, Unitika)
Was used. Furthermore, a 0.06 μm thick zinc sulfide thin film layer was formed on the resin layer. The water vapor transmission rate and light transmittance of these samples were measured. The results are shown in Table 4.

(Effect of the Invention) According to the present invention, by providing a barrier layer in which a zinc sulfide thin film layer, a transparent resin layer, and a zinc sulfide thin film layer are sequentially laminated, a single layer film of a zinc sulfide thin film can be obtained without impairing transparency. A high degree of water vapor barrier property that cannot be achieved can be achieved. Therefore, the packaging film of the present invention can be widely used in the packaging fields of foods, chemicals, and industrial products that require transparency and water vapor barrier properties.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of the packaging film of the present invention. FIG. 2 is a sectional view of a conventional packaging film. 1 ... Substrate film 2,4 ... Zinc sulfide thin film layer 3 ... Transparent resin layer

Claims (1)

[Claims] 1. A transparent plastic film is provided with a barrier layer in which a zinc sulfide thin film layer, a transparent resin layer, and a zinc sulfide thin film layer are sequentially laminated on at least one surface, and the thickness of a single layer of the zinc sulfide thin film layer of the barrier layer. Is 0.02 to 1.0 μm,
A film for packaging, wherein the film thickness of the transparent resin layer is 0.5 μm or more.