JP3120899B2 - Microwave packaging material - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a transparent microwave oven packaging material having a barrier property.

[0002]

2. Description of the Related Art Conventionally, when preserving foods such as cooked foods and semi-cooked foods, packaging is performed with a film having a barrier property against oxygen, water vapor and the like in order to prevent deterioration of quality. Such packaging materials include:
A film made of a polyvinylidene chloride-based resin having a barrier property, a film coated with the polyvinylidene chloride-based resin, or the like, laminated with a non-stretched polypropylene film having a heat-sealing property, or a metal-deposited film or an aluminum foil. Those laminated with a stretched polypropylene film or the like are used. On the other hand, in recent years, with the spread of retort foods and microwave ovens, cooked packaged foods are easily heated in a microwave oven or the like and eaten as they are. For this reason, packaging materials for microwave ovens using a ceramic thin film (silicon oxide) have been proposed. (JP-A-1-202435)

[0003]

The packaging material using the polyvinylidene chloride film is transparent and can see through the contents, but does not have sufficient barrier properties and is not suitable for long-term storage. In addition, this packaging film has high heat resistance (for example, 110 ° C. or more) because the polyvinylidene chloride resin has poor heat resistance.
In this case, there is a problem that the barrier property is remarkably reduced, so that it cannot be used for retort food packaging, and becomes white and opaque at high temperatures.

A packaging film using an aluminum foil or a metal-deposited film has excellent barrier properties and is used for retort food packaging. However, since it is opaque, its contents are not visible, and it has conductivity. It was inconvenient to eat because heating by microwave oven was not possible. On the other hand, a film proposed as a packaging material for a microwave oven using a ceramic thin film (silicon oxide) has no problem in initial barrier properties and heat resistance, but is not colorless and transparent, and is slightly brownish.
The state of the contents is difficult to understand. Furthermore, the bending resistance is not so high, and care must be taken in the subsequent steps such as lamination and bag making and subsequent handling. From this, it is colorless and transparent,
In addition, there has been a demand for a packaging material for a microwave oven which is excellent in gas barrier properties and excellent in practical properties with high bending resistance.

[0005]

A packaging material for a microwave oven according to the present invention is a packaging material having a gas barrier property comprising a plastic substrate and an aluminum oxide-based thin film layer provided on at least one surface of the plastic substrate. A material for a microwave oven, wherein the specific gravity of the thin film is 2.70 to 3.30;
It is a microwave oven material further provided with a heat seal layer.

[0006] The plastic substrate referred to in the present invention may be a plastic film which has good microwave transparency and is not easily degraded by microwave irradiation. A film stretched, cooled and heat-set in the longitudinal and / or width direction, and the organic polymer is polyethylene, polypropylene, polyethylene terephthalate, polyethylene-2,6-naphthalate, nylon 6, nylon 4, nylon 66, nylon 12, polyvinyl chloride, polyvinylidene chloride, polyvinyl alcohol, wholly aromatic polyamide, polyamide imide, polyimide, polyether imide, polysulfone, polyphenylene sulfide, polyphenylene oxide and the like. These (organic polymer) organic polymers may be copolymerized or blended in small amounts with other organic polymers.
Among these, nylon, PET, polypropylene, and saponified ethylene-vinyl acetate copolymer are particularly preferable from the viewpoint of microwave permeability and strength as a packaging bag.

Further, known additives such as an ultraviolet absorber, an antistatic agent, a plasticizer, a lubricant, and a coloring agent may be added to the organic polymer, and the transparency thereof is not particularly limited. However, when used as a transparent gas barrier film, a film having a transmittance of 50% or more is preferred. Plastic substrate in the present invention, as long as the object of the present invention is not impaired, prior to laminating the thin film layer, corona discharge treatment of the film,
A glow discharge treatment or other surface roughening treatment may be performed, or a known anchor coat treatment, printing, or decoration may be performed. The plastic substrate in the present invention preferably has a thickness of 5 to 500 μm,
More preferably, it is in the range of 8 to 300 μm.

In this component, a trace amount (up to 3% of all components) of other components may be contained as long as the characteristics are not impaired. The thickness of the thin film is not particularly limited, but is preferably 5 from the viewpoint of gas barrier properties and flexibility.
0-8000 ° is preferred. To form such an aluminum oxide-based thin film, a PVD method (physical vapor deposition method) such as a vacuum vapor deposition method, a sputtering method, or ion plating, or a CVD method (chemical vapor deposition method) is appropriately used. For example, in a vacuum deposition method, Al or Al ₂ O ₃ is used as a deposition source material, and as a heating method, resistance heating, high-frequency induction heating, electron beam heating, or the like can be used. Further, oxygen, nitrogen, water vapor, or the like may be introduced as a reactive gas, or reactive vapor deposition using means such as ozone addition or ion assist may be used. Further, the production conditions may be changed as long as the object of the present invention is not impaired, such as applying a bias to the substrate, increasing the substrate temperature, or cooling. The same applies to other production methods such as a sputtering method and a CVD method. The product of the present invention may be used as it is, or may be used by laminating or coating a film or a thin layer of another organic polymer.

The specific gravity referred to in the present invention refers to the ratio of the mass of a substance occupying a certain volume at a certain temperature to the mass of a standard substance having the same volume (water at 4 ° C.). The measurement of specific gravity is
Normally, the mass and volume of the object may be measured, and the ratio of the mass to the same volume of water at 4 ° C. may be determined. Then, first, the thin film is peeled off from the substrate or only the substrate is dissolved to form a single film consisting of only the thin film.
It is desirable to use a specific gravity measurement method as described in 7112). For example, in the flotation method, a sample is immersed in a solution having a known specific gravity, and the specific gravity of the thin film can be measured from the flotation state. As this solution, a mixed solution of carbon tetrachloride and bromoform, methylene iodide, or the like can be used. The specific gravity value can also be measured by a density gradient tube method in which a single film is immersed in a solution having a continuous density gradient.

When the specific gravity of the thin film thus obtained is smaller than 2.70, the structure of the aluminum oxide-based thin film becomes coarse, and sufficient gas barrier properties cannot be obtained. When the specific gravity of the thin film is larger than 3.30,
Although the initial gas barrier properties after film formation are excellent, the films are too hard, and the mechanical properties, especially the gelbo properties, are inferior. It is not suitable for use as packaging material. For the above reasons, the specific gravity of the aluminum oxide-based thin film that is preferable as a packaging material for a microwave oven is 2.70 to 3.30, and more preferably 2.70.
80 to 3.20.

Further, the packaging material for a microwave oven according to the present invention comprises:
It is characterized in that the barrier property does not decrease even by high-temperature heat treatment. That is, 100-140 ° C., 10
It can withstand retort treatment for 60 minutes. Therefore, after the food packaged with the packaging material of the present invention is retorted, it can be stored in a microwave oven for a long time after storage, and can be used as a dining table. The packaging material for a microwave oven according to the present invention is a packaging bag for solid materials (hamburger, shomai, gyoza, etc.),
Alternatively, it can be used as a packaging bag for liquid materials (curry, stew, soup, coffee, etc.), and can be heated by a microwave oven while these are packaged. It can also be used for inner bags such as sake packs and heated in a microwave oven. Examples of the form of packaging used include bags, lids, cups, tubes, standing bags, trays or paper packs such as sake, soy sauce, mirin, oil, milk and juice. The heat seal layer may be provided as needed.

As a decoration, the film may be printed, or may be combined with a reinforcing material such as a decorative printing film or a nylon film to form a composite. The packaging material for a microwave oven of the present invention is transparent and has a high barrier property. That is, the oxygen permeability is 4.0 cc / m ² ···
24 hrs or less and a water permeability of 3.0 g / m ²
-24 hrs or less, high barrier properties are maintained even after retort treatment and microwave oven heat treatment.
In addition, since the gelling properties are excellent, the laminating process,
There is little inferiority in the printing process and bag making process. Next, the present invention will be described with reference to examples.

(Embodiment 1) A 12 μm thick PET film was formed by electron beam evaporation using particulate Al ₂ O ₃ (purity 99.9%) having a size of about 3 to 5 mm as an evaporation source. (Toyobo Co., Ltd .: E5007) was used to form an aluminum oxide-based gas barrier thin film. An electron gun (hereinafter referred to as an EB gun) was used as a heating source, and the emission current was 0.7
~ 1.8A. Film feed speed is 40-100
m / min, and a film having a thickness of 500 to 4000 mm was formed. In addition, the vapor pressure is changed by changing the supply amount of oxygen gas, 1 × 1
Conditions were changed from 0 ^-5 to 8 × 10 ^-3 Torr.

The specific gravity of the film thus obtained is determined by PET.
After dissolving the film, the measurement was performed by the floatation / sink method. Furthermore,
For the composite film on PET, an unstretched polypropylene film (OPP film) having a thickness of 60 μm was formed using a two-component curing type polyurethane adhesive (2 μm in thickness).
Dry lamination was performed to obtain a plastic film for packaging. This packaging film is retorted (1
30 ° C x 10 minutes) or after gelbo treatment
The oxygen barrier properties were measured.

Oxygen Permeability Measurement Method The oxygen permeability of the prepared gas barrier film is measured by an oxygen permeability measurement device (OX-TRAN manufactured by Modern Controls).
100). Test method for flex fatigue resistance (hereinafter referred to as gelbo property) The flex fatigue resistance was evaluated using a so-called gelbo flex tester (manufactured by Rigaku Corporation). The conditions are (MIL-B131H) with 112 inch × 8 inch
h into a cylindrical shape having a diameter of 3 (1/2) inch,
Both ends are held, the initial gripping interval is 7 inches, the stroke is 3 (1/2) inch, and a twist of 400 degrees is applied. The reciprocating motion of this operation is repeated 40 times / min.
At a temperature of 20 ° C. and a relative humidity of 65%.
The oxygen permeability measured in this way was very excellent, being 1-2 cc. Furthermore, the result after the 100 times gelbo test also remained at about 2 cc. In addition, even after the retort treatment, a barrier film having a barrier property of 4.0 cc or less was obtained, and a packaging film having excellent overall characteristics was obtained. Using this film, a pillow-type bag with a size of 10 cm x 15 cm was made,
The sample was used for heating characteristics of a microwave oven.

Comparative Example 1 An aluminum oxide-based transparent gas barrier thin film was formed by EB deposition in the same manner as in Example 1, and the obtained sample was subjected to specific gravity measurement and retort treatment, or oxygen barrier after gelbo treatment. Characteristics were measured. As a result, one of the oxygen barrier properties, the barrier properties after the retort treatment, and the gelbo properties became insufficient. Using this film, a sample bag for heating characteristics of a microwave oven was prepared in the same manner as in (Example 1).

(Example 2) As a vapor deposition source, particulate Al (purity 99.9%) having a size of about 3 to 5 mm was used.
An aluminum oxide-based gas barrier thin film was formed on a 12 μm-thick PET film (Toyobo Co., Ltd .: E5000) by high frequency induction heating evaporation. The high-frequency power at that time was 3.5 KW, and the film feed speed was 30 to 100 m.
/ Min, and a film having a thickness of 500 to 4000 mm was formed. The vapor pressure is changed by changing the supply amount of oxygen gas.
Conditions were changed from 0 × 10 ⁻⁵ to 8 × 10 ⁻³ Toor. The specific gravity of the thus obtained film was measured after dissolving the PET film. Hereinafter, in the same manner as in (Example 1), a packaging film was prepared, and the oxygen barrier property was measured.
Further, using this film, a sample bag for heating characteristics of a microwave oven was prepared in the same manner as in (Example 1).

Comparative Example 2 An aluminum oxide-based gas barrier thin film was formed by a high-frequency induction heating vapor deposition method in the same manner as in Example 2, and the obtained sample was subjected to specific gravity measurement and retort treatment or gelbo treatment. Was measured for its oxygen barrier properties. As a result, either the oxygen barrier property, after the retort treatment, or the gelbo properties became insufficient. Further, using this film, a sample bag for heating characteristics of a microwave oven was prepared in the same manner as in (Example 1).
Comparative Example 3 A PET film having a thickness of 12 μm
Dry lamination of an aluminum foil having a thickness of μm, and an unstretched polypropylene film having a thickness of 60 μm was obtained in Example 1.
Dry lamination was performed in the same manner as described above to prepare a bag film. The oxygen barrier properties of this film after retort treatment or gelbo treatment were measured. As a result, both the oxygen barrier property and the gelbo properties after the retort treatment are sufficient. (Comparative Example 4) As a deposition source, particulate SiO (purity 9)
9.9%), and a silicon oxide-based gas barrier thin film was formed by a resistance heating evaporation method. The resulting sample, though transparent, was not colorless and slightly brownish. The oxygen barrier properties of the sample after the specific gravity measurement and the retort treatment or the gelbo treatment were measured. As a result, the oxygen barrier properties and the retort properties were excellent, but the properties after the gelbo treatment were insufficient. Further, using this film, a sample bag for heating characteristics of a microwave oven was prepared in the same manner as in (Example 1).

Next, the suitability for the microwave oven was examined as follows. The bag films of Example 1.2 and Comparative Examples 1 to 4 were made into bags, and each bag was filled with 200 g of curry sauce and heated with a household microwave oven. The time required for microwave heating is 7
It took about 5 seconds. In Comparative Example 3, the conductive aluminum foil sparked and microwave heating was not possible. Further, in order to conduct a long-term storage test, Examples 1 and 2 were used.
2. Representative bags obtained in Comparative Examples 1, 2, and 4
200 g of curry sauce and the like were packed to make a completely sealed sample. For this sample, retort sterilization (120 ° C
× 30 minutes), and the odor, color and taste after being kept at room temperature for 6 months were examined. As a result, Examples of the present invention were normal, but Comparative Examples 1 and 2 showed abnormalities. (Second
Table) In Comparative Example 4, although no abnormality was observed, the color of the light-colored contents was difficult to understand.

[0020]

According to the present invention, in a packaging material having a gas barrier property comprising a plastic substrate and an aluminum oxide-based thin film layer provided on at least one surface of the plastic substrate, the specific gravity of the thin film is 2.70 to 3.30. By doing so, a packaging material having excellent gas barrier properties and suitable for microwave heating can be supplied. Further, the packaging material of the present invention is:
It is possible to provide a colorless and transparent microwave packaging material that is resistant to retort treatment, has high bending resistance, and has excellent overall practical characteristics.

[0021]

[Table 1]

[0022]

[Table 2]

[0023]

[Table 3]

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Toshiyuki Otani 2-1-1 Katata, Otsu-shi, Shiga Prefecture Toyo Spinning Co., Ltd. (72) Inventor Yozo Yamada 2-1-1 Katata, Otsu-shi, Shiga Prefecture Toyo spinning Co., Ltd. research Institute, in the examiner Yoko Nakajima (56) reference Patent Sho 62-101428 (JP, a) JP flat 4-99165 (JP, a) (58 ) investigated the field (Int.Cl. ⁷ , DB name) B32B 1/00-35/00 C08J 7/04

Claims (2)

(57) [Claims] 1. A packaging material having a gas barrier property comprising a plastic substrate and an aluminum oxide-based thin film layer provided on at least one surface of the plastic substrate, wherein the specific gravity of the thin film is 2.70 to 3.30. A packaging material for a microwave oven, which is characterized in that: 2. A packaging material for a microwave oven, further comprising a heat seal layer provided on the thin film layer according to claim 1.