JPH02196652A - laminated film - Google Patents

Abstract

PURPOSE:To obtain a laminated film suitable for a packing material of heated cooked food by applying corona discharge treatment to the surfaces to be laminated of both of a heat shrinkable synthetic resin film and a resin film having heat shrinkability lower than that of the film or having no heat shrinkability and subsequently laminating both films and setting the interfacial adhesive strength of both films to a predetermined value. CONSTITUTION:As a heat shrinkable synthetic resin film 1, one having barrier properties such as a coextrusion composite stretched film having a shrinkage factor of 10% or more in a hot water immersion test for 10 sec at 90-100 deg.C is used and, as a synthetic resin film 2 having low heat shrinkability or no heat shrinkability, a polyolefinic resin film such as a polyethylene film is used. The surfaces to he laminated of both of the heat shrinkable synthetic resin film 1 and the synthetic resin film 2 having low heat shrinkability are subjected to corona discharge treatment before lamination. This corona discharge treatment is performed by adjusting discharge output and a treatment speed so that the adhesive strength of the interface 3a of both films becomes 5-250g/20mm width (20 deg.C). After the discharge treatment, both films are bonded under heating and pressure. By this method, the adhesive strength of both films is made proper and shrink-delamination at the time of heating is smoothly achieved.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a laminated film, and more specifically to packaging for things that are heated and used, particularly packaging materials for microwave-heated food containers that are used under certain heating conditions. This invention relates to a laminated film suitable for.

[Conventional technology]

When cooking foods packaged in synthetic resin film in a microwave oven, various methods are used to prevent the internal pressure inside the package from increasing due to the steam generated during cooking, and to obtain an appropriate steaming effect. is taken. For example, you can cut a part of the bag before cooking, make holes with a toothpick, etc., or make multiple holes in a part of the packaging material or the lid in advance, and then A method is used in which the food is sealed with an adhesive wrapper or barrier film, and then peeled off before cooking to form an opening.

In addition, a lid that makes a sound by blowing out steam is used to notify the completion of cooking and to prevent an increase in internal pressure within the package.

[Problem to be solved by the invention]

However, all of the above-mentioned methods require an operation to create an opening before cooking, which is time-consuming, and if you forget this operation, the packaging bag etc. will be damaged due to the increase in internal pressure during cooking. There is a risk of rupture.

In addition, in the former case, the cooking quality is greatly affected by the position and size of cutting and opening, while in the latter case, the openings are formed to provide moisture and gas barrier properties. The packaged items had to be externally packaged with a separate barrier film, which was time-consuming and led to an increase in packaging costs. Furthermore, lids that let you know when cooking is done make a sound only when the water in the food reaches boiling temperature, so they could not be used for foods that should not be boiled.

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

[Means to solve 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 that has lower heat shrinkage than the synthetic resin film. A laminated film comprising:
After corona discharge treatment is applied to at least one of the bonded surfaces of both films, both synthetic resin films are laminated, and the adhesive strength at the interface of both synthetic resin films is set to 5 to 2.
50g/20! It is characterized by having a lys width (20°C).

Furthermore, the present invention provides that the low heat-shrinkable or non-heat-shrinkable synthetic resin film is a perforated film having a plurality of holes, and that the heat-shrinkable synthetic resin film is a polarized heat-shrinkable synthetic resin film. It is a resin film, and a heat-shrinkable synthetic resin film made of any one of polyvinyl chloride, styrene-butadiene copolymer, and polypropylene is laminated on the other side of the heat-shrinkable synthetic resin film. This includes:

As the heat-shrinkable synthetic resin film, 90 to 10
It is preferable to use a material with barrier properties, such as a coextruded composite stretched film that has a shrinkage rate of 10% or more when immersed in hot water at 0°C for 10 seconds, but depending on the purpose of use of the laminated film and the area in use, etc. , one having an appropriate shrinkage rate can be used. The thickness range is not particularly limited, but 5~
300 ham.

Preferably, a range of 20 to 1100 JJ is appropriate from the viewpoint of cost and strength.

Also, low heat shrinkage or non-heat shrinkage synthetic resin film (
Various materials can be used as the synthetic resin film (hereinafter collectively referred to as low heat shrinkage synthetic resin film), but in particular, polyolefins with excellent heat fusibility such as polyethylene, polypropylene, ethylene-vinyl acetate copolymer, and ionomer resin are used. Examples include resin films. Under the hot water immersion conditions, the film has a shrinkage rate of several percent to 0% and is substantially non-shrinkable, or it is heat-shrinkable but more heat-shrinkable than the heat-shrinkable synthetic resin film. The one with the lowest value is used.

The thickness range of this film is also not particularly limited, but for the same reason as the heat-shrinkable synthetic resin film, the thickness range is 5 to 200.
JJm, preferably in the range of 15 to 1100J1, is suitable.

When the laminated film of the present invention is used as a packaging material for foods heated in a microwave oven, a perforated film having a plurality of through holes is used as the low heat shrinkage synthetic resin film. In this case, it is appropriate to use a synthetic resin film having a shrinkage rate such that the through holes are not blocked by heat shrinkage, particularly a non-heat shrinkable synthetic resin film. The diameter of these holes is 0.1 to 2, and the interval between each hole is 0.5 to 1.
The thickness may be about 0 mm, and it can be provided on the container by piercing with a heating needle or the like.

Before laminating the above-mentioned heat-shrinkable synthetic resin film and the above-mentioned low heat-shrinkable synthetic resin film, it is necessary to subject at least one of the facing film surfaces of both films, that is, the bonding surface, to corona discharge treatment. . This is to lower the temperature during thermocompression bonding of both films below the normal lamination temperature to prevent shrinkage of the heat-shrinkable synthetic resin film, and to adjust the adhesive strength of both films to an appropriate value. be.

The method of corona discharge treatment is not particularly limited, as long as it is sufficient to use a normal corona discharge treatment apparatus equipped with a high frequency oscillator and electrodes and capable of continuous treatment. In this corona discharge treatment, the corona discharge output is adjusted such that the adhesive strength at the interface between the heat-shrinkable synthetic resin film laminated with the pressure tube and the low heat-shrinkable synthetic resin film is 5 to 250 g/2 Oysm width (20°C). , adjust processing conditions such as processing speed as appropriate.

After performing the above-mentioned corona discharge treatment, both films are bonded by thermocompression. The method of thermocompression bonding is not particularly limited either, and the temperature and temperature can be adjusted to a temperature that does not cause large heat shrinkage in the heat-shrinkable synthetic resin film and maintains the adhesion strength at the interface between the two films at an appropriate level as described above. You can do it with pressure. For example, the temperature of the hot roll is 80 to 120°C.

These conditions are appropriately set to optimal conditions depending on the type and thickness of both films, the purpose of use of the laminated film, etc. Also,
By heat-treating the thus laminated films at 30 to 50°C for a long time, for example, 10 hours, the adhesive strength at the interface can be increased within the range of 5 to 250 g/20 me width (20°C).

If the adhesive strength at the interface between the two films after thermocompression bonding is less than 5 tt/20 m1 width (20°C), both films will peel off before use and will not be suitable as a laminated film, and the film will not be suitable for use as a laminated film. / 20 v*-width (20℃
) or more, there is a risk that both films will not peel off during heating.

Furthermore, in order to package foods containing moisture or alcohol, the adhesive strength must be increased to 100 to 250, /20 dragon width (
20° C.) is preferable.

The adhesive strength was measured by pulling a short MT sample with a width of 20-1 in a direction of 180 degrees at a speed of 200 degrees per minute, and the maximum strength at the time of peeling was expressed in g.

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

As the uneven 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 to the heat-shrinkability. for example,
By attaching a synthetic resin film with different heat shrinkability to the other side of the heat-shrinkable synthetic resin film, or by adjusting the stretching direction of the heat-shrinkable synthetic resin film itself, it is possible to reduce uneven heat. Can provide contractility.

Specifically, a biaxially stretched heat-shrinkable synthetic resin film is laminated with a -axially stretched heat-shrinkable synthetic resin film, or an unstretched synthetic resin film is largely stretched in the uniaxial direction, and then It is possible to use a material whose heat shrinkability in both directions is biased by slightly stretching in the perpendicular direction.

As the above-mentioned biaxially stretched heat-shrinkable synthetic resin film, the above-mentioned heat-shrinkable synthetic resin film can be used as is; Polypropylene, polyethylene terephthalate, polystyrene, nylon, etc. can be used. The heat shrinkage rate of this -axially stretched heat-shrinkable synthetic resin film is preferably 10% or more in only one direction when immersed in hot water at 90 to 100°C for 10 seconds. It is preferable that the synthetic resin film has a higher heat shrinkage rate than that of the synthetic resin film. The thickness range of this film is also not particularly limited, but is 5 to 200 mm.
The range is preferably from 10 to 1001 m.

Furthermore, when using a laminate of a biaxially oriented heat-shrinkable synthetic resin film and a uniaxially oriented heat-shrinkable synthetic resin film as an unevenly heat-shrinkable synthetic resin film, the laminate of both or either one of them may be used. This can be carried out by subjecting the film to corona discharge treatment and thermocompression bonding, or by dry lamination using a suitable adhesive. This prevents natural peeling at the interface with the low heat shrinkable synthetic resin film before use, and also limits the direction of shrinkage and peeling of the uneven heat shrinkable synthetic resin film during heating. .

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

Various types of synthetic resin films with different heat shrinkage start temperatures can be used, but in particular, polyvinyl chloride, polyvinyl chloride,
Films such as polypropylene resin and styrene-butadiene copolymer having different shrinkage start temperatures can be used as appropriate.

The heat shrinkage rate of this film is preferably 10% or more when immersed in hot water at 90 to 100°C for 10 seconds, and the thickness is also 5 to 2.
00a, preferably in the range of 10 to 1100a. In particular, if a synthetic resin film with different heat shrinkage start temperatures is used that is hard at room temperature before heating starts, the above-mentioned natural shrinkage of the heat-shrinkable synthetic resin film can be prevented.

〔Example〕

The present invention will be explained in more detail below based on examples.

Example 1 As shown in FIG. 1, a heat-shrinkable synthetic resin film 1 (
A laminated film 3 was created by laminating a shrink 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 shrink film 1, a 40 μm thick coextruded stretched composite sheet consisting of ethylene vinyl acetate copolymer (crimping side)/saponified ethylene vinyl acetate copolymer/nylon resin/ethylene vinyl acetate copolymer was used. . The heat shrinkage characteristics of this shrink film 1 are shown in FIG.

In addition, the perforated film 2 has a hole diameter of 0°1+*s on the entire surface.
, thickness 30 Jr. with hole spacing 1.5 holes 2a formed.
A stretched polypropylene film of m.m was used.

When this perforated film 2 is heated at 100°C for 10 seconds,
is something that hardly ever shrinks.

Then, the bonded surfaces of both films 1.2 were continuously subjected to corona discharge treatment under the following conditions, and then thermocompression bonding was immediately performed.

Corona discharge treatment Corona discharge treatment machine, manufactured by VETAPHONE High frequency oscillation unit; ε-TREATI': Rr: T4-4KW high frequency output; Shrink film...2.7Kv; Perforated film...
・2.0Kv Surface temperature of thermocompression processing roll...105℃ Roll contact pressure...10kg/cmThermocompression bonding speed
...15 m/sln The adhesive strength of the interface 3a between both films 1.2 of the laminated film 3 thus obtained was 70 g/20 mm width (20° C.). The perforated film 2 side of this laminated film 3 was attached to the flange 4a of a container 4 made of polypropylene with an opening of 85 m + s square x 70 m in depth and a flange width of 5 mm, using a sealing mold with a width of 2 + mm under the following conditions. and sealed tightly. At this time, there are 5
Filled with 0ml of tap water.

Sealing conditions Seal mold temperature: 185°C Sealing pressure: 2 kg/cj Re-seal time: 2 sec This container 4 was heated in a microwave oven (NE-M33 manufactured by Matsushita Electric Industrial Co., Ltd.)
0 type, rated high frequency output 500W), output 500W
When the container 4 was heated for 3 minutes, the container 4 was filled with steam, and when the temperature inside the container 4 reached approximately 80°C or higher (heating time was 2 minutes or more), as shown in Figure 3. , the shrink film 1 shrunk and peeled off from the perforated film 2. on the other hand,
The perforated film 2 remained sealed to the flange 4a of the container 4, and steam was appropriately spewed out from the through holes 2a of the perforated film 2.

Example 2 A commercially available microwaveable frozen food (shrimp pilaf) was placed in a container 4 sealed with a laminated film 3 in the same manner as in Example 1.
When 100 g was sealed and cooked under the same conditions as in Example 1, the shrink film 1 similarly shrunk and peeled off from the perforated film 2, and a moderate amount of steam spouted out from the through holes 2a of the perforated film 2. It was possible to make shrimp pilaf with good texture and even heating.

Example 3 The same shrink film and perforated film as in Example 1 were used, and in order to further adjust the shrinkability, a styrene-butadiene copolymer film ("Ceromer S" manufactured by Taishoku Kogyo Co., Ltd., thickness 30 Ham, 100℃X 10s
The shrinkage rate in EC is 296. Each of the above films was subjected to corona discharge treatment under the same conditions as in Example 1, and the composition of perforated film/shrink film/copolymer film was obtained using It was heat-pressed so that

Since the copolymer film and the shrink film in the three-layer laminated film obtained by the above operation have a strong affinity,
The interfacial adhesive strength between them is 300g / 20 va.
width (20℃), and the interfacial adhesion strength between the shrink film and the perforated film is 75/20+em width (2rl
'C).

When this laminated film was hermetically sealed in the opening of a container in the same manner as in Example 1 and heated in a microwave oven, the laminated film consisting of the copolymer film and the shrinkable film shrunk and peeled off while remaining in the laminated state. It had a neat curl-like appearance.

On the other hand, the perforated film remained hermetically sealed on the side of the container, allowing for good cooking.

Example 4 As shown in FIG. 4, a polarized heat-shrinkable film 6 is formed by dry laminating a shrinkable film 1 and a heat-shrinkable uniaxially stretched synthetic resin film 5 (hereinafter referred to as a "-axially shrinkable film") with an adhesive. A laminated film 7 is formed by laminating the perforated film 2.
It was created.

The shrink film 1 has a thickness of 40 mm, which is the same as in Example 1.
A transverse uniaxially stretched film made of polyvinyl chloride and having a thickness of 40 mm was used as the -axis shrink film 5.

The heat shrinkage characteristics of this uneven heat shrinkable film 6 are shown in FIG.

In addition, the perforated film 2 has pores with a diameter of 0°6 mm on the entire surface.
A polypropylene film having a thickness of 50 μm and having through holes 2a formed with a hole interval of 7 was used. This perforated film 2 has 1
When heated at 00°C for 10 seconds, there is almost no shrinkage.

Then, the bonding surfaces of the shrink film 1 and the perforated film 2 of the uneven heat shrink film 6 are bonded using the corona discharge treatment machine, and the crab shrink film for high frequency...2. OKv: perforated film...2.7Kv After processing, thermocompression bonding was performed under the same conditions as in Example 1.

Interface 7 between shrink film 1 and perforated film 2 of unevenly heat shrinkable film 6 of laminated film 7 thus obtained
The adhesive strength of a was 110K/20 degrees (20°C).

The perforated film 2 side of this laminated film 7 is made of polypropylene and has an opening diameter of 88 am x depth of 70 m + *.

On the flange 8a of the round container 8 (see Fig. 6), the flange 5 has a dragon width.
Hermetically sealing was carried out under the same conditions as in Example 1 using a sealing mold having a width of 3IIl■. At this time, the container 8 was filled with 50 ml of tap water.

When this container 8 was heated in a microwave oven in the same manner as in Example 1, the container 8 was filled with steam, and the container 8 was heated.
When the temperature inside reaches about 80°C or higher (heating time around 1 minute 30 seconds), the uneven heat shrinkable film 6 shrinks as shown in FIGS. 6 and 7 (a) and (b). Then, it was peeled off from the perforated film 2. The peeling direction coincided with the stretching direction of the -axis shrink film 5.

On the other hand, the perforated film 2 remained sealed to the flange 8a of the container 8, and steam was appropriately spewed out from the through holes 2a of the perforated film 2.

Example 5 100 pieces of commercially available microwave frozen food (shrimp pilaf) were sealed in a container made by sealing with a laminated film formed in the same manner as in Example 4, and cooked under the same conditions as Example 1. Similarly, the uneven heat shrinkable film shrank and peeled off. The direction coincided with the stretching direction of the uniaxial shrink film.

In addition, a suitable amount of steam was ejected from the holes in the perforated film, making it possible to produce shrimp pilaf with a good texture and even heating.

Example 6 Instead of the uniaxial shrink film in Example 4, a polyvinyl chloride film (heat-shrinkable hard synthetic resin film, hereinafter referred to as hard film) having a heat shrinkage rate shown in FIG. 8 was used, and a perforated film was used. A laminated film was created according to the following procedure so as to have a film/shrink film/hard film structure.

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

Next, both the bonded surface of this laminated film (shrink film) and the bonded surface of the above-mentioned hard film are subjected to corona discharge treatment under the following conditions, so that the structure becomes a hard film/shrink film/perforated film. Thermocompression bonding was carried out under the same conditions as in Example 1.

The processing conditions at this time are as follows.

High frequency output; Shrink film...2.0Kw; -Axis shrink film...2. OKw The adhesive strength at the interface between the shrink film and the perforated film of the laminated film thus obtained was 110 g/
The width was 20 W (20°C). In addition, the adhesive strength at the interface between the shrink film and the hard film is 220/20■
■Width (20°C).

Using this laminated film, seal it in a polypropylene round container in the same manner as in Example 4, and in the same manner as in Example 1.
When the film was heated in a microwave oven, peeling occurred when the film temperature reached 62° C. (heating time: 85 seconds).

Example 7 The same procedure as in Example 6 was conducted except that the hard film was a polypropylene film having a heat shrinkage rate shown in FIG. 8, and the film temperature was 83°C (
Peeling occurred when the heating time reached 98 seconds).

Example 8 The same procedure as in Example 6 was carried out except that the hard film was a styrene-butadiene copolymer film having the heat shrinkage rate shown in FIG. Peeling occurred at a time of 95 seconds).

Comparative Example When the perforated film and shrink film or copolymer film used in each of the above examples were thermocompression bonded under the same conditions without corona discharge treatment, the adhesive strength at the interface of each film was The weight was also less than 5 g/20 dragon width (20° C.), and each film peeled off before use, which was inconvenient as a laminated film.

The laminated film of the present invention is not limited to the above embodiments, but can also be formed into a bag shape, and can be used for various purposes such as packaging foods and other items that are dissolved in or extracted with hot water. .

Furthermore, even if a film without holes is used as a low heat shrinkable synthetic resin film, only the uneven heat shrinkable synthetic resin film can be shrunk and peeled off. If you use a transparent film with a low heat shrinkage synthetic resin film, you can protect the items stored inside from light before heating, provide various indications, and make it opaque during heating. When the heat-shrinkable synthetic resin film shrinks and peels off, it is possible to visually observe the heated state of the article inside the transparent low-heat-shrinkable synthetic resin film.

Furthermore, by applying appropriate printing on a low heat-shrinkable synthetic resin film, and heating it to shrink and peel off only the opaque heat-shrinkable synthetic resin film that covers the surface, it is possible to create an expression that it has been heated, etc. It can also be used for things like toys or hit bushes.

〔Effect of the invention〕

As explained above, the laminated film of the present invention is produced by laminating a heat-shrinkable synthetic resin film and a low-heat-shrinkable synthetic resin film after corona discharge treatment on their bonded surfaces, and increasing the adhesive strength of both films to 5 to 250. tc/20ya
m width (20°C), so under normal conditions they do not peel off and remain laminated, but when heated, the heat-shrinkable synthetic resin film shrinks and peels off, leaving a low heat-shrinkable synthetic resin film on the surface. It is possible to obtain an unprecedented laminated film. Furthermore, by performing a corona discharge treatment when bonding both films together, the adhesive strength of both films can be adjusted to an appropriate level, and shrinkage and peeling during heating can be smoothly performed.

Then, by using a perforated film as a low heat-shrinkable synthetic resin film and using this perforated film inside as a packaging material for microwave-heated foods, the outer heat-shrinkable synthetic resin film shrinks and peels off during cooking. Since only the above-mentioned perforated film is left, proper heating and cooking can be carried out without bursting or boiling over. In addition, before heating, there is a heat-shrinkable synthetic resin film on the outside of the perforated film, so by using a film with sufficient barrier properties for this heat-shrinkable synthetic resin film, food items stored inside can be heated. can maintain its freshness for a long period of time. Therefore, there is no need to package the food with a separate barrier film or the like, and cooking can be easily and easily performed without making holes, cutting, peeling the package, etc. during cooking.

In addition, by using an unevenly heat-shrinkable synthetic resin film as the heat-shrinkable synthetic resin film, the peeling direction during heating peeling can be kept in a constant direction, so if the container is heated while sealed, the peeling direction will be It becomes constant and the appearance when peeled off becomes good. For example, it is suitable as a sealing film for a container that has a handle or the like and requires constant peeling direction.

Furthermore, the other side of the heat-shrinkable synthetic resin film is made of polyvinyl chloride and styrene-butadiene copolymer.

By laminating heat-shrinkable synthetic resin films made of any one type of polypropylene, the peeling temperature can be adjusted, making it possible to adapt to the cooking conditions of various foods.

[Brief explanation of the drawing]

Figure 1 is a cross-sectional view of the laminated film produced in Example 1 of the present invention, Figure 2 is a heat shrinkage characteristic diagram of the heat-shrinkable synthetic resin film used in Example 1, and Figure 3 is the same <Example 1>. Fig. 4 is a cross-sectional view of the laminated film prepared in Example 4, and Fig. 5 is a cross-sectional view showing the state in which the heat-shrinkable synthetic resin film has shrunk and peeled off. Fig. 5 shows the container prepared in Example 4. Figures 6 and 7 show the heat shrinkage characteristics of the unevenly heat-shrinkable film used in Example 4, and Figure 6 shows the container prepared in Example 4. A cross-sectional view showing the state, FIG. 7 is a plan view as well, and FIG. 8 is a sectional view of Example 6.
8 is a diagram showing the heat shrinkage characteristics of the hard film used in Examples 8 to 8. FIG. 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 shrinkable film

Claims (1)

[Claims] 1. A laminated film comprising a heat-shrinkable synthetic resin film and a low-heat-shrinkable or non-heat-shrinkable synthetic resin film that has lower heat shrinkage than the synthetic resin film, comprising:
After corona discharge treatment is applied to at least one of the bonded surfaces of both films, both synthetic resin films are laminated, and the adhesive strength at the interface of both synthetic resin films is set to 5 to 2.
A laminated film characterized by having a width of 50g/20mm (20°C). 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 holes. 3. The laminated film according to claim 1, wherein the heat-shrinkable synthetic resin film is an unevenly heat-shrinkable synthetic resin film. 4. A heat-shrinkable synthetic resin film made of any one of polyvinyl chloride, styrene-butadiene copolymer, and polypropylene is laminated on the other side of the heat-shrinkable synthetic resin film. The laminated film according to claim 1.