JPH0622976B2 - Plastic film for packaging - Google Patents

Description

TECHNICAL FIELD The present invention relates to a plastic film for packaging which is excellent in gas barrier property, transparency, adhesiveness, non-curl property, and resistance to boiling and retorting.

(Prior Art) A gas barrier plastic film is used for packaging foods, pharmaceuticals, chemicals, etc. to prevent permeation of water vapor and oxygen. When a higher gas barrier property is required to prevent the deterioration of the contents, the following is used.

A plastic film laminated with aluminum foil, or a plastic film with aluminum vapor deposited on the surface.

Polyvinylidene chloride, vinylidene chloride as the main component,
Other compounds copolymerizable with this, such as vinyl chloride,
A film made of vinylidene chloride resin such as a copolymer with methyl acrylate, methyl methacrylate, acrylonitrile and the like, and a vinylidene chloride resin coat film obtained by coating these vinylidene chloride resin on a film made of polypropylene, polyester, polyamide and the like.

A polyvinyl alcohol film such as a polyvinyl alcohol film or an ethylene-vinyl alcohol copolymer film.

Films deposited with silicon compounds such as biaxially stretched nylon film and biaxially stretched polyester film (Japanese Patent Publication No.
3-12953), polyethylene terephthalate film, biaxially oriented polypropylene film, etc., on which magnesium oxide is vapor-deposited (JP-A-60-2753).
2).

(Problems to be Solved by the Invention) However, those conventionally used have the following drawbacks.

The ones have excellent barrier properties against water vapor, oxygen, etc., and also have excellent resistance to boiling and retort,
It is opaque and the contents cannot be seen from the outside.

Although they have a gas barrier property against water vapor and oxygen, they are not sufficient and are not suitable for packaging which requires a high gas barrier property.

The water vapor barrier property is inferior in water vapor barrier property, and the oxygen barrier property is also deteriorated under the condition of high humidity. Therefore, when using a polyvinyl alcohol film, usually, polypropylene film, polyethylene film,
A film having a water vapor barrier property such as a polyester film is laminated. However, such a laminated film also has insufficient gas barrier properties. Therefore, in order to use such a laminated film for packaging which requires a high gas barrier property, the laminated film as a whole must be made considerably thick, which impairs the transparency and flexibility of the laminated film. .

They do not fully serve their purpose when a high degree of gas barrier properties is required. Further, the workability at the time of packaging such as a biaxially stretched nylon film or a biaxially stretched polyester film, which is easily curled, is poor and the adhesion is also poor.

The present invention eliminates the above-mentioned various drawbacks and provides a plastic film for packaging which is excellent in gas barrier property, transparency, adhesion, non-curl property, and resistance to boiling and retorting.

(Means for Solving the Problems) The present invention provides a plastic film having a thickness of 100 μm or less on at least one surface thereof by using an isocyanate compound / saturated polyester mixed resin.
A plastic film for packaging, wherein a resin layer having a thickness of / 1000 to 100/1000 is formed, and a silicon oxide thin film having a thickness of 5 to 500 nm is formed on the resin layer.

The plastic film of the present invention is made from various plastics such as polyester such as polyethylene terephthalate and polyethylene-2,6-naphthalate, polyamide such as nylon 6 and nylon 12, polypropylene, polycarbonate, polystyrene, polyvinyl chloride, polyvinylidene chloride and the like. It is a transparent film. The plastic film may be stretched or unstretched, but a stretched plastic film is preferable from the viewpoint of gas barrier property.
The stretching may be uniaxial stretching or biaxial stretching.

The plastic film may contain inorganic particles, organic particles, an organic lubricant, an antistatic agent, a stabilizer, a dye, a pigment, and an organic polymer, if necessary.

The thickness of the plastic film is 100 μm or less.
If the thickness of the plastic film exceeds 100 μm,
It is not easy to obtain a plastic film having excellent anti-curl property and adhesiveness, and it is not suitable for boiling and retorting because it is too thick.

The resin layer is formed of a resin of an isocyanate compound / saturated polyester mixture. As the isocyanate compound, hexamethylene diisocyanate, diphenylmethane diisocyanate, a condensate of 3 mol of hexamethylene diisocyanate and 1 mol of trimethylolpropane, triphenylmethane triisocyanate, and various other isocyanate compounds can be used. The mixing ratio is 80 to 30% of isocyanate compound and 20 to saturated polyester.
70% is preferable. If the isocyanate compound content is more than 80% and the saturated polyester content is less than 20%, the adhesion will be poor, and if the isocyanate compound content is less than 30% and the saturated polyester content is more than 70%, the adhesion property and the non-curling property will be poor.

The thickness of the resin layer is 1/1000 that of a plastic film.
To 100/1000 is preferable, and 5/1000 to
75/1000 is particularly preferred. When the resin layer is thicker than 100/1000 of the plastic film, it is useful for imparting the non-curl property, but the adhesion with the silicon oxide is poor, the flexibility of the plastic film is impaired, and the handling of the plastic film becomes difficult. . On the other hand, if it is thinner than 1/1000, it is not useful for imparting the non-curl property, and the gas barrier property is not improved so much due to uneven coating.

Examples of the method for forming the resin layer on at least one surface of the plastic film include various resin liquid coating methods such as a gravure coating method and a reverse coating method.

In order to improve the coatability and adhesion of the resin liquid forming the resin layer to the plastic film, the surface of the plastic film is roughened, corona-treated, plasma-treated, flame-treated, radiation-treated, before coating the resin liquid. The surface may be modified by various treatments such as chemical treatment.

A silicon oxide thin film is formed on the resin layer. When the silicon oxide thin film is formed directly on the plastic film, the plastic film is likely to curl and the adhesion is poor.

The silicon oxide thin film may be formed of SiO or SiO ₂ by a known thin film forming means such as a vacuum deposition method, a sputtering method and an ion plating method. For example, in the case of the vacuum vapor deposition method, a roll of plastic film on which a resin layer is formed is installed in a take-up type vacuum vapor deposition machine, SiO or SiO ₂ is used, and a vacuum is applied at 10 ⁻³ to 10 ⁻⁶ Torr. The evaporation may be performed by heating with a beam, high frequency induction heating, or resistance heating, and continuous deposition may be performed while winding the plastic film. Also, Si, SiO, or SiO
^It is also possible to employ a reactive vapor deposition method in which ² is used and O ² gas is supplied.

Incidentally, the silicon oxide thin film, even if calcium, magnesium, or their oxides are mixed as impurities,
If it is 10% by weight or less, the gas barrier property is not extremely lowered, and the present invention includes such a thing.

The thickness of the silicon oxide thin film is preferably in the range of 5 to 500 nm. If it is thinner than 5 nm, the gas barrier property is insufficient. If it is thicker than 500 nm, the transparency is poor, and the plastic film is likely to be curled, and further, the silicon oxide thin film itself is likely to be cracked or peeled.

The silicon oxide thin film should be transparent with a light transmittance of 75% or more. This is so that the contents can be seen when used for packaging.

A transparent plastic film can be formed on the silicon oxide thin film in order to protect the silicon oxide thin film, to color the entire film, and to impart adhesiveness.

To form a transparent plastic film on the silicon oxide thin film, various transparent plastic films are laminated or a transparent plastic coating film is formed. For forming transparent plastic films, vinyl chloride resins such as polyethylene and ethylene copolymers, polypropylene and propylene copolymers, ethylene-vinyl acetate copolymers, ionomers, polyvinyl chloride and their copolymers are used. Vinylidene chloride resin such as vinylidene chloride-vinyl chloride copolymer, polyester resin such as polyethylene terephthalate, and the like can be used.

The present invention may also form an adhesive layer partially or entirely on at least one side. If a transparent plastic film is not formed on the silicon oxide thin film, or if the transparent plastic film formed on the silicon oxide thin film does not have adhesiveness, by doing this, It is useful in obtaining bags for later packaging. The adhesive layer may be formed by a part coating method, a whole surface coating method, or the like.

(Example) Next, this invention is demonstrated based on an Example and contrasting with a comparative example.

The moisture permeability, oxygen permeability, light transmittance, adhesion strength, and non-curl are measured or evaluated by the following methods,
Further, the thickness of the silicon oxide thin film was measured by a crystal type film thickness meter.

"Moisture Permeability" Using a Permatran-WI type moisture permeability measuring device manufactured by Modern Control Co., Ltd., measurement was performed at a temperature of 40 ° C and a relative humidity of 90%.

"Oxygen permeability" It was measured under the conditions of a temperature of 25 ° C and a relative humidity of 90% using an OX-TRAN100 type oxygen permeability measuring device manufactured by Modern Control.

"Light transmittance" The total light transmittance was measured by the method of JIS K-6714.

"Adhesion strength" It was measured according to the T-peel test method of JIS K-6854.

"Non-curling property" The non-curling property of a product cut to a length of 20 cm and a width of 5 cm was visually evaluated, and a product without curl was marked with ⊚, and a product with curl was marked with x.

Example 1 An isocyanate compound (Coronate L manufactured by Nippon Polyurethane Industry Co., Ltd.) was formed on one surface of a 12 μm thick biaxially stretched film (stretching ratio 3 × 3 times) polyester film (PET film).
And a saturated polyester (Vylon 300 manufactured by Toyobo Co., Ltd.) in a ratio of 50:50 were applied and dried to form a resin layer having a thickness of about 8/1000 (about 0.1 μm) of the polyester film. .

Next, on the resin layer, under a vacuum of 8 × 10 ⁻⁵ Torr,
By a high frequency induction heating method, SiO having a purity of 99.9% was heated and evaporated to form a silicon oxide thin film having a thickness of 50 nm to obtain a plastic film for packaging of the present invention.

The moisture permeability, oxygen permeability, and light transmittance of the obtained packaging plastic film were measured, and the non-curled product was visually evaluated.

The results are shown in Table 1.

Example 2 The thickness of the resin layer was 50/1000 of that of polyester film.
The thickness was set to 0.6 μm, and the same procedure as in Example 1 was performed.

Example 3 The same as Example 1 except that the thickness of the silicon oxide thin film was 100 nm.

Example 4 The thickness of the resin layer is 50/1000 of that of polyester film.
(0.6 μm) and the thickness of the silicon oxide thin film was 300 nm.

Example 5 The packaging plastic film of the present invention obtained in Example 1 has a thickness of 40 nm on the surface of a silicon oxide thin film having a thickness of 50 nm.
An unstretched polypropylene film (CPP film) with a thickness of 2 μm and a two-component curing type polyurethane adhesive (thickness 2 μm
m) was dry-laminated to obtain a packaging plastic film of the present invention in which a transparent plastic film was formed on a silicon oxide thin film.

The moisture permeability, the oxygen permeability, the light transmittance, and the adhesion strength between the polyester film and the unstretched polypropylene film of the obtained plastic film for packaging were measured, and the anti-curl property was visually evaluated.

Further, the obtained plastic film for packaging was used and heat-sealed with the unstretched polypropylene film side as the inner side to obtain a bag having an inner size of 12 cm × 18 cm. Curry food "bon curry" (Otsuka foods) 200 in this bag
It was filled with g, vacuum packed, and boiled at 100 ° C. for 30 minutes. In addition, a bag filled with curry food "Bon curry" (Otsuka foods) was prepared in the same manner, and the bag was stored at 120 ° C for 3 days.
Retort treatment was performed for 0 minutes.

The moisture permeability, the oxygen permeability, the light transmittance, and the adhesion strength between the polyester film and the unstretched polypropylene film were measured after the boil and retort treatments, and the non-curl property was visually evaluated.

The results are shown in Table 1.

Example 6 The procedure of Example 5 was repeated, except that the unstretched polypropylene film (CPP film) to be dry-laminated was the plastic film for packaging of the present invention obtained in Example 2.

Example 7 The procedure of Example 5 was repeated, except that the plastic film for packaging of the present invention obtained in Example 3 was used as the film for dry laminating the unstretched polypropylene film (CPP film).

Example 8 The procedure of Example 5 was repeated, except that the unstretched polypropylene film (CPP film) to be dry-laminated was the plastic film for packaging of the present invention obtained in Example 4.

Comparative Example 1 8 × 10 ⁻⁵ was provided on one side of a biaxially stretched polyester film (PET film) having a thickness of 12 μm (stretching ratio 3 × 3 times).
Of high purity 99.9% S by high frequency induction heating method under vacuum
The io was heated and evaporated to form a silicon oxide thin film having a thickness of 50 nm to obtain a plastic film having the silicon oxide thin film.

The water vapor permeability, oxygen permeability, and light transmittance of the obtained product were measured, and the non-curled product was visually evaluated.

The results are shown in Table 1.

Comparative Example 2 The thickness of the resin layer was 0.5 / 100 of that of the polyester film.
Same as Example 1 except that the thickness was 0 (0.006 μm).

Comparative Example 3 Same as Example 1 except that the thickness of the silicon oxide thin film was 3 nm.

Comparative Example 4 An unstretched polypropylene film (CPP film) having a thickness of 40 μm was formed on the silicon oxide thin film surface of the plastic film having the silicon oxide thin film obtained in Comparative Example 1.
A two-component curing type polyurethane adhesive (thickness: 2 μm) was used for dry lamination to obtain a plastic film having a silicon oxide thin film in which a transparent plastic film was formed on the silicon oxide thin film.

The moisture permeability, oxygen permeability, light transmittance, and adhesion strength between the polyester film and the unstretched polypropylene film of the obtained product were measured, and the uncurling property was visually evaluated.

Further, using the obtained product, heat sealing was performed with the unstretched polypropylene film side being the inner side, and the inner dimension was 12c.
A bag measuring m × 18 cm was obtained. This bag is filled with 200 g of curry food "Bon curry" (Otsuka food) and vacuum packed, and 1
Boil treatment was performed at 00 ° C. for 30 minutes. In addition, a bag filled with curry food “Bon curry” (Otsuka foods) was prepared by the same method, and retort-treated at 120 ° C. for 30 minutes.

The moisture permeability, the oxygen permeability, the light transmittance, and the adhesion strength between the polyester film and the unstretched polypropylene film were measured after the boil and retort treatments, and the non-curl property was visually evaluated.

The results are shown in Table 1.

Comparative Example 5 Comparative Example 5 was carried out in the same manner as Comparative Example 4 except that the film obtained by dry laminating the unstretched polypropylene film (CPP film) was the plastic film having the silicon oxide thin film obtained in Comparative Example 2.

Comparative Example 6 Comparative Example 6 was carried out in the same manner as Comparative Example 4 except that the film obtained by dry laminating the unstretched polypropylene film (CPP film) was the plastic film having the silicon oxide thin film obtained in Comparative Example 3.

The following can be seen from Table 1.

(1) The plastic film for packaging of the present invention has low moisture permeability, low oxygen permeability, excellent gas barrier property, high light transmittance and excellent transparency, high adhesion strength and excellent adhesion. The curling property is also excellent, and these properties are good even after the boil and retort treatment, and the present invention is excellent in the boil and retort resistance. (Example 1
-See Example 8) (2) On the other hand, when there is no resin layer (Comparative Examples 1 and 4)
(See) has high water vapor transmission rate and oxygen permeability, poor gas barrier properties and poor adhesion. Also, after boil and retort treatment, water vapor transmission rate and oxygen permeability are further increased, and adhesion strength is greatly reduced. , Inferior in retort resistance.

If the resin layer is too thin (see Comparative Examples 2 and 5),
If the silicon oxide thin film is too thin even if the resin layer is not too thin (see Comparative Examples 3 and 6), the water vapor permeability and oxygen permeability are high, the gas barrier property is poor, and the boiling and retort resistance is also poor.

(Effects of the Invention) The present invention is excellent in gas barrier property, transparency, adhesion, non-curl property, and resistance to boiling and retort, and further, strength,
It is also excellent in terms of flexibility and economy. Therefore, it can be widely used for packaging that requires high gas barrier properties such as foods, pharmaceuticals, chemicals, etc.
Its utility value is extremely high for chemicals and industrial use.

Claims (3)

[Claims] 1. A plastic film having a thickness of 100 .mu.m or less is coated on at least one side with a resin of an isocyanate compound / saturated polyester mixture,
A plastic film for packaging, characterized in that a resin layer having a thickness of / 1000 to 100/1000 is formed, and a silicon oxide thin film having a thickness of 5 to 500 nm is formed on the resin layer. 2. The packaging plastic film according to claim 1, wherein a transparent plastic film is formed on the silicon oxide thin film. 3. The plastic film for packaging according to claim 1, wherein an adhesive layer is partially or entirely formed on at least one surface.