JP2781981B2 - Laminated film - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a laminated film, and more particularly to a packaging of a product to be heated and used, particularly to a packaging material of a food container heated by a microwave oven used under a constant heating condition. It relates to a suitable laminated film.

[Conventional technology]

When cooking food packed in a synthetic resin film using a microwave oven, various methods are used to prevent the internal pressure inside the package from rising due to steam generated during heating and to obtain a moderate steaming effect. Has been taken. For example, a method of cutting a part of a bag before cooking, a method of making a hole with a fingernail branch or the like, or forming a plurality of openings in a part of a packaging material or a closing lid in advance, and A method of sealing the upper portion with an adhesive label or a barrier film and peeling them off before cooking to form an opening is used. In addition, a sealing lid that emits sound by blowing steam is used to notify the completion of cooking and to prevent an increase in internal pressure in the package.

[Problems to be solved by the invention]

However, in each of the above-mentioned methods, an operation for providing an opening before cooking is required, which is troublesome, and when this operation is forgotten and cooking is performed, the packaging pressure increases due to an increase in internal pressure during cooking. Risk of rupture.

In the case of the former, the cookable finish greatly depends on the position and size of the hole when cutting or drilling, and in the latter case, a package with an opening formed in order to impart moisture proof and gas barrier properties. The product must be packaged with another barrier film, which is troublesome and leads to an increase in packaging cost. Further, the lid material that notifies the user of the completion of cooking by sound only sounds when the temperature of water in the food reaches a boiling point, and cannot be used for food that must not be boiled.

Therefore, an object of the present invention is to provide a laminated film suitable for a packaging material of this type of cooked food.

[Means for solving the problem]

In order to achieve the above object, the laminated film of the present invention comprises a heat-shrinkable synthetic resin film and a low-heat-shrinkable or non-heat-shrinkable synthetic resin film having a lower heat-shrinkability than the synthetic resin film. A laminated film, wherein at least one of the bonding surfaces of the two films is subjected to a corona discharge treatment, the two synthetic resin films are laminated, and the adhesive strength at the interface between the two synthetic resin films is 5
~ 250g / 20mm width (20 ℃).

Further, the present invention provides that the low heat-shrinkable or non-heat-shrinkable synthetic resin film is a perforated film having a plurality of through-holes, and the heat-shrinkable synthetic resin film is a synthetic heat-shrinkable synthetic resin film. A resin film, a heat-shrinkable synthetic resin film made of any one of polyvinyl chloride, styrene-butadiene copolymer, and polypropylene laminated on the other surface of the heat-shrinkable synthetic resin film; Is included.

As the heat-shrinkable synthetic resin film, 90-100
It is preferable to use a film having barrier properties, such as a co-extruded composite stretched film having a shrinkage of 10% or more in hot water immersion at 10 ° C. for 10 seconds, but depending on the purpose of use of the laminated film and the area at the time of use, A material having an appropriate shrinkage ratio can be used. Although the thickness range is not particularly limited, it is 5 to 300 μm.
m, preferably in the range of 20 to 100 μm, from the viewpoint of cost and strength.

Low heat shrinkable or non-heat shrinkable synthetic resin film (hereinafter collectively referred to as low heat shrinkable synthetic resin film)
Although various types can be used, in particular, polyethylene, polypropylene, ethylene-vinyl acetate copolymer,
A polyolefin-based resin film excellent in heat-sealing property such as an ionomer resin is exemplified. And, under the hot water immersion conditions, the shrinkage is several% to 0%, and is substantially non-shrinkable or heat shrinkable, but is more heat shrinkable than the heat shrinkable synthetic resin film. Is used. Although the thickness range of this film is not particularly limited, it is 5 to 20 for the same reason as the heat-shrinkable synthetic resin film.
A range of 0 μm, preferably 15 to 100 μm is appropriate.

When the laminated film of the present invention is used as a packaging material for a microwave-heated food, a perforated film having a plurality of through holes is used as the low heat shrinkable synthetic resin film. In this case, it is appropriate to use a synthetic resin film having a shrinkage factor such that the through hole is not blocked by heat shrinkage, particularly a non-heat shrinkable synthetic resin film. The through-hole may have a diameter of about 0.1 to 2 mm and an interval between the through-holes of about 0.5 to 10 mm, and can be easily provided by piercing a heating needle or the like.

Before the heat-shrinkable synthetic resin film and the low-heat-shrinkable synthetic resin film are laminated, it is necessary to subject at least one of the film surfaces facing each other, that is, the bonding surface, to corona discharge treatment. . This is to prevent the shrinkage of the heat-shrinkable synthetic resin film by lowering the temperature at the time of thermocompression bonding of both films from the normal lamination temperature, and to adjust the adhesive strength of both films to an appropriate value. is there.

The corona discharge treatment method is not particularly limited as long as a normal corona discharge treatment device that includes a high-frequency oscillator and an electrode and can perform continuous treatment can be used. The corona discharge treatment is performed so that the adhesive strength at the interface between the heat-shrinkable synthetic resin film and the low-heat-shrinkable synthetic resin film laminated by pressure is 5 to 250 g / 20 mm width (20 ° C.). Processing conditions such as processing speed are appropriately adjusted.

Then, after performing the corona discharge treatment, both films are thermocompression-bonded. The method of this thermocompression bonding is also not particularly limited, and a temperature and a temperature at which the contact strength at the interface between the two films can be made appropriate as described above without causing large heat shrinkage in the heat-shrinkable synthetic resin film. It can be done with pressure.
For example, as a hot roll temperature, 80 to 120 ° C. is used. These are appropriately set under optimum conditions depending on the type and thickness of both films, the purpose of use of the laminated film, and the like. Further, by subjecting the film thus laminated to a heat treatment at 30 to 50 ° C. for a long time, for example, 10 hours, the contact strength at the interface can be increased within the range of 5 to 250 g / 20 mm width (20 ° C.). .

If the bonding height of the interface between the two films after thermocompression bonding is 5 g / 20 mm width (20 ° C) or less, the two films peel off before use and are not suitable as a laminated film.
If the width is 0 mm or more (20 ° C.) or more, both films may not peel off during heating. Further, in order to package food containing water or alcohol, the adhesive strength is preferably set to 100 to 250 g / 20 mm width (20 ° C.).

As the method of measuring the adhesive strength, a 20 mm wide strip sample was pulled in a direction of 180 degrees at a speed of 200 mm and the maximum strength at the time of peeling was expressed in g.

In addition, by using a heat-shrinkable synthetic resin film as the heat-shrinkable synthetic resin film, the direction of peeling of the heat-shrinkable synthetic resin film can be made constant.

As the above-mentioned heat-shrinkable synthetic resin film, various kinds can be used as long as the heat-shrinkability in one direction when heated is greater than the heat-shrinkability in a direction perpendicular thereto. For example, by attaching a synthetic resin film different from the heat-shrinkable synthetic resin film to the other surface of the heat-shrinkable synthetic resin film, or by adjusting the stretching direction of the heat-shrinkable synthetic resin film itself, It can impart an uneven heat shrinkage. Specifically, a uniaxially stretched heat-shrinkable synthetic resin film is laminated on a biaxially stretched heat-shrinkable synthetic resin film, or a non-stretched synthetic resin film is stretched largely in the uniaxial direction, and is perpendicular to it. In such a case, a material having a small heat-shrinkability in both directions by stretching the film in a small direction can be used.

As the above-mentioned biaxially stretched heat-shrinkable synthetic resin film, the above-described heat-shrinkable synthetic resin film can be used as it is, and as the uniaxially stretched heat-shrinkable synthetic resin film, for example, polyvinyl chloride, polypropylene ,
Polyethylene terephthalate, polystyrene, nylon and the like can be used. As the heat shrinkage of the uniaxially stretched heat-shrinkable synthetic resin film, those having 10% or more in only one direction in 10 seconds of immersion in hot water at 90 to 100 ° C. are preferable. Those having a higher heat shrinkage than the synthetic resin film of the above are preferred. Although the thickness range of this film is not particularly limited, it is 5 to 200 μm,
Preferably, the range of 10 to 100 μm is appropriate.

In addition, as the unevenly heat-shrinkable synthetic resin film, when using a laminate of a biaxially stretched heat-shrinkable synthetic resin film and a uniaxially stretched heat-shrinkable synthetic resin film, the lamination of both is one or both. Can be subjected to a corona discharge treatment and thermocompression bonding, or by dry lamination with an appropriate adhesive. Thereby, it is possible to prevent spontaneous peeling at the interface with the low heat shrinkable synthetic resin film before use, and to restrict the direction of shrinkage / peeling of the unevenly heat shrinkable synthetic resin film during heating. .

Furthermore, the shrinkage start temperature can be adjusted by strongly bonding the synthetic resin film having a different heat shrink start temperature to the other surface of the heat shrinkable synthetic resin film.

Various synthetic resin films having different heat shrink start temperatures can be used. In particular, films having different shrink start temperatures, such as polyvinyl chloride, polypropylene resin, and styrene-butadiene copolymer, may be appropriately used. Can be used. The heat shrinkage of this film also
It is preferably 10% or more after immersion in hot water at 90 to 100 ° C. for 10 seconds, and the thickness is suitably from 5 to 200 μm, preferably from 10 to 100 μm. In particular, when a synthetic resin film having a different heat shrink start temperature is used at room temperature before heating is started, natural shrinkage of the heat shrinkable synthetic resin film can be prevented.

〔Example〕

Hereinafter, the present invention will be described in more detail based on examples.

Example 1 As shown in FIG. 1, a heat-shrinkable synthetic resin film 1
A laminate film 3 was formed by laminating a shrinkable film (hereinafter, referred to as a shrink film) and a low heat shrinkable synthetic resin film 2 having through holes 2a (hereinafter, referred to as a perforated film).

As the shrinkable film 1, a coextruded stretched composite sheet having a thickness of 40 μm composed of ethylene vinyl acetate copolymer (pressure-bonding side) / saponified ethylene vinyl acetate copolymer / nylon resin / ethylene vinyl acetate copolymer is used. Was. FIG. 2 shows the heat shrinkage characteristics of the shrinkable film 1.

As the perforated film 2, a stretched polypropylene film having a thickness of 30 μm and having through holes 2a with a hole diameter of 0.1 mm and a hole interval of 1.5 mm formed on the entire surface was used. This perforated film 2 has 100
Heating at ℃ for 10 seconds hardly shrinks.

Then, the bonded surfaces of the films 1 and 2 were continuously subjected to corona discharge treatment under the following conditions, and then immediately subjected to thermocompression bonding.

Corona discharge treatment Corona discharge treatment machine; High frequency oscillator manufactured by VETAPHONE; ε-TREATER ET4-4KW High frequency output; Shrink film: 2.7Kw; Perforated film: 2.0Kw Thermocompression treatment Roll surface temperature: 105 ° C Roll contact pressure … 10kg / cm Thermocompression bonding speed… 15m / min Both films of the laminated film 3 thus obtained
The adhesive strength of the interface 3a between 1 and 2 was 70 g / 20 mm width (20 ° C.). The perforated film 2 side of the laminated film 3 is placed on a flange 4a of a container 4 having an opening of 85 mm square × 70 mm in depth and a flange of 5 mm in width using a 2 mm-wide sealing die under the following conditions. Hermetically sealed. At this time, the container 4 was filled with 50 ml of tap water.

Sealing condition Sealing mold temperature… 185 ° C Sealing pressure… 2kg / cm ² Sealing time… 2sec This container 4 is placed in a microwave oven (NE-M330 manufactured by Matsushita Electric Industrial Co., Ltd.).
Mold, rated high-frequency output 500W) and heated for 3 minutes at 500W output, the vessel 4 was filled with steam, and the temperature inside the vessel 4 became about 80 ° C or more (heating time 2 minutes or more) At that point, as shown in FIG. 3, the shrinkable film 1 shrank and peeled off from the perforated film 2. On the other hand, the perforated film 2 was still sealed by the flange 4 a of the container 4, and the steam was appropriately ejected from the through holes 2 a of the effective film 2.

Example 2 100 g of a commercially available frozen food for a microwave oven (shrimp pilaf) was sealed in a container 4 formed by sealing with a laminated film 3 in the same manner as in Example 1, and heated and cooked under the same conditions as in Example 1. Then, the shrinkable film 1 shrank and peeled off from the perforated film 2, and steam was spouted appropriately from the through-holes 2a of the perforated film 2 to produce a shrimp pilaf with good texture and without uneven heating.

Example 3 A styrene-butadiene copolymer film ("Ceromer S" manufactured by Okura Kogyo Co., Ltd .: 30 μm thick, Each of the above films was subjected to a corona discharge treatment under the same conditions as in Example 1 using a film having a shrinkage ratio of 2% in the vertical direction and 1.7% in the horizontal direction at 100 ° C. × 10 sec. The thermocompression bonding was carried out so as to have a structure of a perforated film / shrink film / copolymer film.

Since the copolymer film and the shrinkable film in the three-layer laminated film obtained by the above operation have strong affinity, the interfacial adhesive strength between them is 300 g / 20 mm width (20 ° C.). The interfacial adhesion strength with the perforated film was 75 g / 20 mm width (20 ° C.).

This laminated film was hermetically sealed in the opening of the container in the same manner as in Example 1, and was similarly heated and cooked by a microwave oven. As a result, the laminated film composed of the copolymer film and the shrinkable film was shrunk and peeled off in a laminated state. And a well-curled appearance. On the other hand, the perforated film remained hermetically sealed on the container side, and good cooking could be performed.

Example 4 As shown in FIG. 4, perforated heat-shrinkable film 6 obtained by dry laminating shrinkable film 1 and heat-shrinkable uniaxially stretched synthetic resin film 5 (hereinafter referred to as uniaxially shrinkable film) with an adhesive was used. Film 2 was laminated to form laminated film 7.

The shrinkable film 1 has the same thickness as that of the first embodiment.
A co-extruded stretched composite sheet of 40 μm was used, and the uniaxially shrinkable film 5 was a 40 μm-thick horizontal uniaxially stretched film made of polyvinyl chloride.

FIG. 5 shows the heat shrinkage of the unevenly heat shrinkable film 6.

Also, as the effective film 2, a polypropylene film having a thickness of 50 μm and having a through hole 2a with a hole diameter of 0.6 mm and a hole interval of 7 mm formed on the entire surface was used. The perforated film 2 hardly shrinks when heated at 100 ° C. for 10 seconds.

And the shrink film 1 of the above-mentioned heat-shrinkable film 6
And the bonded surface of the perforated film 2 were processed as a high-frequency output; a shrink film: 2.0 Kw; a perforated film: 2.7 Kw using the corona discharge treatment machine, and then thermocompression bonded under the same conditions as in Example 1. Was done.

The interface between the shrinkable film 1 of the non-uniform heat-shrinkable film 6 of the laminated film 7 thus obtained and the perforated film 2
The adhesive strength of 7a was 110 g / 20 mm width (20 ° C.).

The perforated film 2 side of the laminated film 7 is attached to a flange 8a of a round container 8 (see FIG. 6) having an opening diameter of 88 mm × depth of 70 mm and a flange of 5 mm width (see FIG. 6). Using a mold, sealing was performed under the same conditions as in Example 1. At this time, the container 8 was filled with 50 ml of tap water.

When the container 8 was placed in a microwave oven and heated in the same manner as in Example 1, the container 8 was filled with steam, and the temperature in the container 8 was about 80 ° C. or more (heating time: about 1 minute 30 seconds). 6 and FIGS. 7 (a) and 7 (b), the non-uniformly heat-shrinkable film 6 shrinks and the perforated film 2 as shown in FIGS.
Peeled off. The direction in which the film was peeled coincided with the stretching direction of the uniaxially shrinkable film 5.

On the other hand, the perforated film 2 was still sealed by the flange 8a of the container 8, and the steam was appropriately ejected from the through holes 2a of the perforated film 2.

Example 5 A commercially available frozen food (shrimp pilaf) for microwave oven was sealed in a container prepared by sealing with a laminated film formed in the same manner as in Example 4, and heated and cooked under the same conditions as in Example 1. The shrinkable heat-shrinkable film shrank and peeled off.
The direction coincided with the stretching direction of the uniaxially shrinkable film. In addition, steam was spouted from the perforations of the perforated film appropriately, and a shrimp pilaf with good texture without heating unevenness could be produced.

Example 6 Instead of the uniaxially shrinkable film in Example 4, a polyvinyl chloride film having a heat shrinkage rate shown in FIG. 8 (a heat-shrinkable hard synthetic resin film, hereinafter referred to as a hard film) is used as an effective film. A laminated film was prepared by the following procedure so as to have a configuration of / shrink film / hard film.

First, the bonding surface of the shrink film 1 and the perforated film 2 was subjected to corona discharge treatment and thermocompression bonding under the same conditions as in Example 4 to form a perforated film / shrink film laminated film.

Next, after performing a corona discharge treatment on both the bonded surface (shrink film) of the laminated film and the bonded surface of the hard film under the following conditions, the hard film / shrink film / perforated film is formed. Example 1
Thermocompression bonding was performed under the same conditions as described above.

 The processing conditions at this time are as follows.

High frequency output; Shrink film: 2.0 Kw; Uniaxial shrink film: 2.0 Kw The adhesive strength of the interface between the shrink film and the perforated film of the laminated film thus obtained is 110 g / 20 mm width (2
0 ° C). The adhesive strength at the interface between the shrink film and the hard film was 220 g / 20 mm width (20 ° C.).

This laminated film was sealed in a polypropylene round container in the same manner as in Example 4 and heated in a microwave oven as in Example 1. The film temperature was 62 ° C. (heating time 85 ° C.). Second), peeling occurred.

Example 7 In Example 6, except that the hard film was a polypropylene-based film having a heat shrinkage shown in FIG.
When performed in the same manner as in Example 6, the film temperature was 83 ° C.
(Heating time 98 seconds), peeling occurred.

Example 8 The procedure of Example 6 was repeated, except that the styrene-butadiene copolymer film having the heat shrinkage shown in FIG. 8 was used as the hard film. When the time reached 95 seconds), peeling occurred.

Comparative Example Without performing corona discharge treatment using the perforated film and the shrinkable film or the copolymer film used in each of the above examples, and subjected to thermocompression bonding under similar conditions, the adhesive strength at the interface of each film was Was less than 5 g / 20 mm width (20 ° C.), and each film peeled off before use, which was inconvenient as a laminated film.

Incidentally, the laminated film of the present invention is not limited to the above embodiment,
It can be formed into a bag, dissolved in food or other hot water,
Alternatively, it can be used for various uses such as packaging of those extracted with hot water.

In addition, even if a non-porous film is used as the low heat shrinkable synthetic resin film, only the non-uniform heat shrinkable synthetic resin film can be similarly contracted and peeled, so that, for example, the heat shrinkable synthetic resin film is opaque or appropriately. If a transparent film is used for the synthetic resin film with low heat shrinkage using a film that has been subjected to various printing, it protects the goods stored inside from light before heating and performs various displays,
When the opaque heat-shrinkable synthetic resin film shrinks and peels off during heating, the heated state of the article in the transparent low heat-shrinkable synthetic resin film can be visually observed.

Furthermore, appropriate printing is applied to the low heat shrinkable synthetic resin film, and only the opaque heat shrinkable synthetic resin film covering the surface is shrunk and peeled off by heating, so that the expression such as heated or the like can be obtained. It can also be used for things such as simple toys or hits.

〔The invention's effect〕

As described above, the laminated film of the present invention is laminated after performing the corona discharge treatment on the bonding surface of the heat-shrinkable synthetic resin film and the low heat-shrinkable synthetic resin film, and the adhesive strength of both films is 5 to 250 g. / 20mm width (20 ° C), heat-shrinkable synthetic resin film shrinks and peels off when heated and keeps laminated state without peeling in normal state, and low heat shrinkable synthetic resin film comes out on the surface It is possible to obtain an unprecedented laminated film. In addition, by performing corona discharge treatment when laminating both films,
Adhesive strength of both films can be made appropriate strength,
Shrinkage peeling during heating can be performed smoothly.

By using a perforated film as a low heat shrinkable synthetic resin film, and using the perforated film as an inner side to form a packaging material for a microwave-heated food, the outer heat shrinkable synthetic resin film shrinks and peels off during cooking. Since only the perforated film is used, appropriate heating can be performed without bursting or spilling. Before heating, there is a heat-shrinkable synthetic resin film outside the perforated film, so that the heat-shrinkable synthetic resin film uses a film with sufficient barrier properties to store food etc. inside. Can be maintained for a long time. Therefore, it is not necessary to wrap it with another barrier film or the like, and it is possible to easily perform heating cooking without performing drilling, cutting, peeling of the package, and the like during cooking.

In addition, by using a non-uniform heat-shrinkable synthetic resin film as the heat-shrinkable synthetic resin film, the peeling direction at the time of heating and peeling can be made a fixed direction. It becomes constant and the appearance becomes good at the time of peeling. For example, the container has a handle or the like, and is suitable as a sealing film for a container in which it is required to stabilize the direction of peeling.

Further, by laminating a heat-shrinkable synthetic resin film made of any one of polyvinyl chloride, styrene-butadiene copolymer and polypropylene on the other surface of the heat-shrinkable synthetic resin film, the peeling temperature can be reduced. Since it can be adjusted, it can be made to correspond to the cooking conditions of various foods.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of the laminated film prepared in Example 1 of the present invention, FIG. 2 is a diagram of the heat shrinkage characteristic of the heat-shrinkable synthetic resin film used in Example 1, and FIG. FIG. 4 is a cross-sectional view showing a state in which a heat-shrinkable synthetic resin film has been peeled off, FIG. 4 is a cross-sectional view of a laminated film prepared in Example 4, and FIG. FIG. 6 and FIG. 7 show the container prepared in Example 4, and FIG. 6 shows a state in which the heat-shrinkable synthetic resin film is shrunk and peeled off. FIG. 7 is a plan view of the same, and FIG.
FIG. 9 is a drawing showing the heat shrinkage characteristics of the hard films used in Nos. 1 to 8; 1 ... heat-shrinkable synthetic resin film, 2 ... low heat-shrinkable synthetic resin film, 2a ... through-hole, 3, 7 ... laminated film, 3a, 7a ... interface, 6 ... uneven heat shrinkage the film

Claims (4)

(57) [Claims] 1. A laminated film comprising a heat-shrinkable synthetic resin film and a low-heat-shrinkable or non-heat-shrinkable synthetic resin film having a lower heat-shrinkability than the synthetic resin film. After performing a corona discharge treatment on at least one of the bonding surfaces of the two synthetic resin films, the adhesive strength at the interface between the two synthetic resin films was set to 5 to 250 g / 20 mm width (20 ° C.). Laminated film. 2. The laminated film according to claim 1, wherein the low heat shrinkable or non-heat shrinkable synthetic resin film is a perforated film having a plurality of through holes. 3. The laminated film according to claim 1, wherein the heat-shrinkable synthetic resin film is a heat-shrinkable synthetic resin film. 4. The other surface of the heat-shrinkable synthetic resin film is coated with polyvinyl chloride, styrene-butadiene copolymer,
2. A heat-shrinkable synthetic resin film made of any one of polypropylene is laminated.
The laminated film according to the above.