JPH061379A - Packing material for microwave oven - Google Patents

Abstract

PURPOSE:To provide a packing material for a microwave oven, which is excellent in the bending-resistance and the gas-barrier as a packing film. CONSTITUTION:In a packing material having a gas-barrier function, composed of a plastic base material and a thin film layer comprising aluminum oxide and siliceous oxide applied on at least one side of the plastic base material as a chief component, the ratio of the aluminum oxide in the thin film is >=20% and <=99% in weight. When the specific gravity of the thin film and the composite ratio of the aluminum oxide in the thin film are expressed in the following relation; D=0.01A+b, where D is the s.g. of the thin film, A is the weight percent of the aluminum oxide in the thin film, a packing material for a microwave oven, which is excellent in a gas-barrier and a bending-resistance applicable for the microwave oven heating and also pratical characteristics as a whole, can be obtained by defining the s.g. of the thin film within the range of 1.6<=b<=2.2.

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 barrier properties.

[0002]

2. Description of the Related Art Conventionally, when storing foods such as cooked foods and semi-cooked foods, a film having a barrier property against oxygen, water vapor and the like is used to prevent deterioration of quality. As such a packaging material,
A film made of polyvinylidene chloride resin having a barrier property, or a film obtained by coating the above polyvinylidene chloride resin with a non-stretched polypropylene film having a heat-sealing property, a metal vapor deposition film or an aluminum foil is not used. A laminated product such as a stretched polypropylene film is used. On the other hand, in recent years, along with the widespread use of retort foods and microwave ovens, it has become widespread to simply cook cooked packaged foods in a microwave oven or the like and eat them as they are. Therefore, a packaging material for microwave ovens using a ceramic thin film (silicon oxide) has also been proposed. (JP-A-1-202435)

[0003]

The packaging material using the polyvinylidene chloride film is transparent and allows the contents to be seen through, but it does not have sufficient barrier properties and is not suitable for long-term storage. Also, since this packaging film is inferior in heat resistance of the polyvinylidene chloride resin, it can be used at high temperatures (for example, 1
At 10 ° C. or higher), the barrier property remarkably decreases. Therefore, it cannot be used for packaging for retort food, and there is a problem that it becomes white and becomes opaque at high temperature.

A packaging film using an aluminum foil or a metal vapor-deposited film has an excellent barrier property and is used for retort food packaging. However, since it is opaque, its contents cannot be seen and it is electrically conductive. As a result, it is inconvenient to eat because it cannot be heated by a microwave oven. On the other hand, regarding the film proposed as a packaging material for microwave ovens that uses a ceramic thin film (silicon oxide), there is no problem with the initial barrier property and heat resistance, but it is not colorless It is difficult to understand the state of things. Further, the bending resistance is not so high, and it is necessary to pay attention to the subsequent steps such as laminating and bag making and the subsequent handling. Therefore, a packaging material for a microwave oven, which is colorless and transparent, has an excellent gas barrier property, has a high bending resistance, and has excellent practical characteristics, has been desired.

[0005]

The packaging material for a microwave oven according to the present invention is a packaging material having a gas barrier property, which comprises a plastic film and a thin film layer containing aluminum oxide or silicon oxide as a main component. A packaging material for a microwave oven, characterized in that the proportion of aluminum oxide therein is 20% by weight or more and 99% by weight or less, and the specific gravity of the thin film satisfies the following formula: D = 0.01A + b ( However, D: specific gravity of the thin film, A: weight% of aluminum oxide in the thin film) 1.6 ≤ b ≤ 2.2. Alternatively, the packaging material for a microwave oven further comprises a heat seal layer provided on the thin film layer.

The plastic substrate referred to in the present invention may be a plastic film which has good microwave transparency and is not easily deteriorated by microwave irradiation. The film is a film that has been stretched, cooled and heat set in the longitudinal direction and / or the width direction, and as the organic polymer, polyethylene, polypropylene, polyethylene terephthalate, polyethylene-2,6-naphthalate, nylon 6, nylon, nylon 4, nylon 66, nylon 12, polyvinyl chloride, polyvinylidene chloride, polyvinyl alcohol, wholly aromatic polyamide, polyamideimide, polyimide, polyetherimide, polysulfone, polyphenylene sulfide, polyphenylene oxide and the like. Further, these (organic polymer) organic polymers may be copolymerized or blended with a small amount of another organic polymer.
Among these, nylon, PET, polypropylene, and saponified ethylene-vinyl acetate copolymer are particularly preferable in terms 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, those having a transmittance of 50% or more are preferable. As long as the plastic substrate in the present invention does not impair the object of the present invention, prior to laminating the thin film layer, the film is subjected to corona discharge treatment,
Glow discharge treatment or other surface roughening treatment may be performed, and known anchor coat treatment, printing, or decoration may be performed. The thickness of the plastic substrate in the present invention is preferably in the range of 5 to 500 μm,
More preferably, it is in the range of 8 to 300 μm.

The thin film containing aluminum oxide or silicon oxide as a main component in the present invention is considered to consist of a mixture of aluminum oxide and silicon oxide, or a compound. Aluminum oxide here means A
It is composed of a mixture of various aluminum oxides such as 1, AlO, and Al ₂ O ₃ , and the content ratio of each in aluminum oxide varies depending on the preparation conditions. Silicon oxide means Si, Si
It is considered that they are made of O, SiO _2, etc., and their ratios also differ depending on the preparation conditions. The proportion of aluminum oxide in the thin film in the present invention is 20% by weight or more, 99
% By weight or less, preferably 30% by weight or more, 95
It is less than or equal to wt. Further, a small amount (up to 3% with respect to all the components) of other components may be contained in this component as long as the characteristics are not impaired. Although the thickness of the thin film is not particularly limited, it is preferably 50 to 8000 Å, more preferably 70 to 5,000 Å, from the viewpoint of gas barrier property and flexibility.

For forming such a thin film containing aluminum oxide or silicon oxide as a main component, a vacuum deposition method or a sputtering method is used.
A PVD method (physical vapor deposition method) such as a method or ion plating, or a CVD method (chemical vapor deposition method) is appropriately used. For example, in the vacuum vapor deposition method, a mixture of Al ₂ O ₃ and SiO ₂ or Al and SiO ₂ is used as a vapor deposition source material, and heating methods include resistance heating, high frequency induction heating, and electron beam heating. Etc. can be used.
Further, as the reactive gas, oxygen, nitrogen, water vapor or the like may be introduced, or reactive vapor deposition using means such as ozone addition or ion assist may be used. In addition, such as applying a bias to the substrate, raising the substrate temperature, or cooling it,
The preparation conditions may be changed as long as the object of the present invention is not impaired. The same applies to other preparation methods such as the sputtering method and the CVD method. Further, the product of the present invention may be used as it is, but may be used by laminating or coating another organic polymer film or thin layer.

The specific gravity referred to in the present invention is the ratio of the mass of a substance that occupies 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
Usually, the mass and volume of an object may be measured and the ratio to the mass of water of the same volume at 4 ° C. may be obtained, but it is difficult to measure the volume in the measurement of the thin film of the present invention. Therefore, first, the thin film is peeled from the substrate, or only the substrate is melted to form a single film made of only the thin film, and then (JIS K
7112), it is desirable to use a specific gravity measurement method. For example, in the float-sink method, the sample can be dipped in a solution of known specific gravity, and the specific gravity of the thin film can be measured from the floating state. As this solution, a mixed solution of carbon tetrachloride and bromoform, or methylene iodide can be used. The specific gravity value can also be measured by a density gradient tube method in which a single membrane is immersed in a solution having a continuous density gradient.

The relationship between the specific gravity value of the thin film thus obtained and the weight% of aluminum oxide in the thin film is D
= 0.01A + b (D: specific gravity of thin film, A:% by weight of aluminum oxide in the thin film), when the value of b is less than 1.6, aluminum oxide and silicon oxide are the main components. Therefore, the structure of the thin film becomes rough, and sufficient gas barrier properties cannot be obtained. Further, in the case where the value of the specific gravity of the thin film is larger than 2.2 in b value,
Although the initial gas barrier property after film formation is excellent, the film becomes too hard, the mechanical property, especially the gelbo property is inferior, due to the post-process such as laminating and bag making, and the subsequent handling,
The gas barrier property is likely to deteriorate, and it is not suitable for use as a packaging material. For the above reasons, as a packaging material for a microwave oven, the specific gravity of a preferable thin film containing aluminum oxide or silicon oxide as a main component is such that the relation between the specific gravity of the thin film and the aluminum oxide composition ratio in the thin film is D =
When expressed by the relational expression of 0.01A + b (D: specific gravity of thin film, A: weight% of aluminum oxide in the thin film), the value of b is 1.6 to 2.2, and more preferably 1.7.
To 2.1.

Further, the packaging material for a microwave oven of the present invention is
There is a feature that the barrier property is not deteriorated even by high temperature heat treatment. That is, 100 to 140 ° C., 10
Can withstand retort treatment for 60 minutes. Therefore, it is possible to retort a food packaged with the packaging material of the present invention, heat it in a microwave oven as it is, and use it for a meal after long-term storage. The packaging material for a microwave oven of the present invention is a packaging bag for solid matter (hamburger steak, pork mai, gyoza, etc.),
Alternatively, it can be used as a packaging bag for liquid substances (curry, stew, soup, coffee, etc.), and can be heated in a microwave oven while being packaged. It can also be used as an inner bag such as a sake pack and heated in a microwave oven. The form of packaging used includes bags, lids, cups, tubes, standing bags, trays or liquor, soy sauce, mirin, oil, milk, juice, and other paper packs and the like. The heat seal layer may be provided if necessary.

As a decoration, printing may be performed on the film, or a decorative printing film or a reinforcing material such as a nylon film may be laminated 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 3.0 cc / m ² ·
Less than 24 hrs and moisture permeability of 3.0 g / m ²
-It is 24 hours or less, and maintains a high barrier property even after retort treatment and microwave oven heat treatment.
In addition, because it has excellent gelbo characteristics, there is little deterioration in the laminating process, printing process, and bag making process, and even after it is made into a bag,
Do not take extra care when handling it. Next, the present invention will be described with reference to examples.

Example 1 As a vapor deposition source, particulate Al ₂ O ₃ (purity 99.5%) and SiO ₂ (purity 99.9%) with a size of about 3 to 5 mm were used, and an electron beam was used. 12 μm thick PET film (Toyobo Co., Ltd .: E
5100), an aluminum oxide silicon oxide gas barrier thin film was formed. The vapor deposition material was divided into two parts with a carbon plate without mixing, and one electron gun (hereinafter referred to as EB gun) was used as a heating source to separate Al ₂ O ₃ and SiO ₂ respectively. Heated in time division. The emission current of the EB gun at that time was changed to 0.8 to 2.2 A, the heating ratio to Al ₂ O ₃ and SiO ₂ was changed to 20:10 to 50:10, and the composition was changed. Film feed speed is 30-1
The film thickness was changed to 20 m / min to form a film having a thickness of 500 to 4000 Å. The vapor pressure was changed from 1 × 10 ⁻⁵ to 8 × 10 ⁻³ Torr by changing the supply amount of oxygen gas.

The specific gravity of the thus-obtained film is determined by PET.
After the film was dissolved, the film was measured by the float-sink method. Further, a 60 μm-thick unstretched polypropylene film (OPP film) was dry-laminated to the composite film on PET using a two-component curing type polyurethane adhesive (thickness 2 μm) and packaged. To obtain a plastic film. Retort treatment (13
After 0 ° C. × 10 minutes) or gelbo treatment, the oxygen barrier property was measured.

Method for measuring oxygen transmission rate The oxygen transmission rate of the prepared gas barrier film is measured by an oxygen transmission rate measuring apparatus (OX-TRAN manufactured by Modern Controls Co., Ltd.).
100). -Test method of flex fatigue resistance (hereinafter gelbo property) Flex fatigue resistance was evaluated using a so-called gelbo flex tester (manufactured by Rigaku Kogyo Co., Ltd.). The condition is (MIL-B131H) 112 inch x 8 inc.
The sample piece of h was made into a cylindrical shape with a diameter of 3 (1/2) inch,
Both ends are held, the initial gripping interval is set to 7 inches, a twist of 400 degrees is applied at a stroke of 3 (1/2) inch, and this reciprocating motion is repeated 40 times / min.
At a temperature of 20 ° C. and a relative humidity of 65%.
The oxygen transmission rate measured in this way was extremely excellent, about 1 cc. Furthermore, the result after the 100th gelbo test was only about 2 cc. Also, after the retort treatment, a packaging film having a barrier property of 3.0 cc or less and excellent overall characteristics was obtained. Using this film, a pillow type bag with a size of 10 cm × 15 cm is prepared,
The sample was used for microwave oven heating characteristics. (Tables 1 and 2)

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

(Example 2) As a vapor deposition source, particulate Al (purity 99.9%) and SiO having a size of about 3 to 5 mm were used.
₂ (Purity 99.9%) and 12 μm thick PET film (Toyobo Co., Ltd .: E
5007), an aluminum oxide silicon oxide-based gas barrier thin film was formed. The high frequency power at that time is 5.5 kW
Then, the film feed speed was changed to 30 to 120 m / min to form a film having a thickness of 500 to 4000 Å. The vapor pressure is 1.0 × 10 ^-5 by changing the supply amount of oxygen gas.
The conditions were changed up to 8 × 10 ⁻³ Torr. After dissolving the PET film with the specific gravity of the film thus obtained,
It was measured. A sample bag for microwave heating characteristics was prepared in the same manner as in the following (Example 1). (Tables 3 and 4)

Comparative Example 2 An aluminum oxide silicon oxide gas barrier thin film was formed by the high frequency induction heating vapor deposition method as in Example 2, and the obtained sample was subjected to specific gravity measurement and retort treatment, or gel-bottle treatment. The oxygen barrier property after the treatment was measured. As a result, either the oxygen barrier property, after the retort treatment, or the gelbo property became insufficient. Also, using this film, a sample bag for microwave oven heating characteristics was prepared in the same manner as in (Example 1). Comparative Example 3 A PET film having a thickness of 12 μm has a thickness of 12
An aluminum foil having a thickness of 60 μm was dry laminated, and an unstretched polypropylene film having a thickness of 60 μm was used in Example 1.
Dry lamination was carried out in the same manner as 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 property after the retort treatment are sufficient. (Comparative Example 4) Particulate SiO (purity: 9
9.9%) was used to form a silicon oxide gas barrier thin film by a resistance heating vapor deposition method. Although the obtained sample was transparent, it was not colorless but slightly brownish. Oxygen barrier properties of this sample were measured after specific gravity measurement and retort treatment or gelbo treatment. As a result, the oxygen barrier property and the retort property were excellent, but the properties after gelbo treatment were insufficient. Also, using this film, a sample bag for microwave oven heating characteristics was prepared in the same manner as in (Example 1).

Next, the suitability for a microwave oven was examined as follows. The representative 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 in a household microwave oven. Microwave heating time is
It was about 75 seconds. In Comparative Example 3, the conductive aluminum foil sparked and the microwave oven could not be heated. Furthermore, in order to perform a long-term storage stability test (Table 5),
The representative bags obtained in Examples 1 and 2 and Comparative Examples 1, 2 and 4 were filled with 200 g of curry sauce and the like to prepare a completely sealed sample. This sample was subjected to retort sterilization (120 ° C. × 30 minutes) treatment, and the odor, color, and taste were examined after holding at room temperature for 6 months. As a result, the examples of the present invention were normal, but the comparative examples 1 and 2 showed abnormalities. Further, in Comparative Example 4, although no abnormality was observed, the color of the light-colored contents was difficult to understand.

[0021]

EFFECT OF THE INVENTION In a packaging material having a gas barrier property, which comprises a plastic substrate and a thin film layer containing aluminum oxide or silicon oxide as a main component provided on at least one surface of the plastic substrate, the proportion of aluminum oxide in the thin film Is 20% by weight or more and 99% by weight or less, and the relationship between the specific gravity of the thin film and the composition ratio of aluminum oxide in the thin film is D = 0.01A + b (D: specific gravity of thin film, A: weight of aluminum oxide in thin film). %) When expressed by the relational expression
By setting the specific gravity of the thin film within the range represented by 1.6 ≦ b ≦ 2.2, the thin film is excellent in gas barrier property and has high bending resistance suitable for heating in a microwave oven and has excellent overall practical properties. A microwave packaging material can be provided.

[0022]

[Table 1]

[0023]

[Table 2]

[0024]

[Table 3]

[0025]

[Table 4]

[0026]

[Table 5]

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Internal reference number FI technical display location B65D 81/34 V 7191-3E (72) Inventor Toru Otani 2-1-1 Katata, Otsu City, Shiga Prefecture No. Toyobo Co., Ltd. General Research Institute (72) Inventor Toshio Uno 2-1-1 Katata, Otsu City, Shiga Prefecture Toyobo Co., Ltd. General Research Institute (72) Inventor Yozo Yamada 2-1-1 Katata, Otsu City, Shiga Prefecture No. Toyobo Co., Ltd.

Claims (2)

[Claims] 1. A packaging material having a gas barrier property, comprising a plastic base material and a thin film layer containing aluminum oxide or silicon oxide as a main component provided on at least one surface of the plastic base material, wherein aluminum oxide is contained in the thin film. Is 20% by weight or more and 99% by weight or less, and the specific gravity of the thin film satisfies the following formula. D = 0.01A + b where D: specific gravity of the thin film, A: weight% of aluminum oxide in the thin film 1.6 ≦ b ≦ 2.2 2. The packaging material for a microwave oven according to claim 1, further comprising a heat seal layer provided on the thin film layer.