JP2768616B2 - Heat shrinkable film for food packaging - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a food packaging film for packaging a food or an object to be packaged such as a food container.

[0002]

2. Description of the Related Art Conventionally, packaging of foods such as fruits and vegetables, fresh fish, meat, prepared foods, packaging of foods placed on lightweight trays of plastics, and packaging of foods in containers with lids, etc., are usually carried out. This is done by stretch wrapping with film. Stretch wrapping is to wrap an object to be wrapped with the film stretched. Such a film is called a so-called pre-packaging film, and a film made of a polyvinyl chloride resin (PVC) is widely used. The film has transparency and anti-fogging properties, so even when packaging food containing moisture, the contents can be seen well without fogging, and since it has self-adhesiveness, after packaging foods etc., the film may be loose. There is no. Furthermore, since it has elastic recovery properties, there is a characteristic that wrinkles and loosening do not occur after pressing the film. However, films made of polyvinyl chloride resin are excellent in suitability and workability of an automatic packaging machine, but have a problem in environmental or safety and hygiene, which has been particularly emphasized in recent years. For this reason,
In place of the polyvinyl chloride resin as a material of the above-mentioned film, a film made of a polyolefin-based resin having few problems on the environment or safety and health is widely used.

[0003]

However, although the polyolefin resin film is rarely regarded as a problem in terms of the environment and health and safety, it is inferior in elastic recovery power to the polyvinyl chloride resin described above, so that the polyolefin resin film cannot be used. If the film is pressed by hand after packaging the tray on which the food is placed, the surface of the film is wrinkled or loosened, resulting in a problem that a beautiful package finish is hardly obtained and the commercial value is significantly reduced.

In order to solve this drawback, it is necessary to impart heat shrinkage to a film made of a polyolefin resin, and to give the film a shrink property by performing biaxial stretching to improve the packaging finish. However, in order to obtain heat shrinkability, there are many things that are not effective unless the temperature is close to the melting point, and because the stretching orientation is strongly applied, the elongation of the film itself is poor and the applicable range of the packaged material to the film width However, the orientation of the film becomes clear due to the strong stretching, and the directionality of the film becomes clear, and once a hole is formed in the film, tears propagate from the hole, making it difficult to collect.

Accordingly, the present invention solves the above-mentioned conventional problems, and has a suitable shrink wrapping suitability and also has a stretch wrapping suitability. An object of the present invention is to provide a system-based food packaging film (hereinafter, referred to as a film).

[0006]

The present inventors have conducted various studies to solve the above-mentioned problems, and as a result, have found that the essential properties of the film are transparency, antifogging property, self-adhesiveness and elastic recovery. We have developed a practically desirable polyolefin-based film that has this and can solve the above problems.

That is, according to the present invention, a vinyl acetate content of 3.about.12% by weight is contained on both surfaces of an intermediate layer mainly composed of an ethylene-methacrylic acid copolymer resin having a methacrylic acid content of 8 to 12% by weight.
A resin layer containing 5 to 30% by weight of an ethylene-vinyl acetate copolymer as a main component is provided.
SUMMARY OF THE INVENTION A heat-shrinkable film for food packaging formed by ration molding .

Hereinafter, the film of the present invention will be described in detail. The film of the present invention comprises an intermediate layer mainly composed of an ethylene-methacrylic acid copolymer resin and a resin mainly composed of an ethylene-vinyl acetate copolymer laminated on both surfaces thereof, and is contained in each layer. the content of methacrylic acid or vinyl acetate Ri certain range near and blow
There is a technical feature in inflation molding at a ratio of 5 or more .

First, the ethylene-methacrylic acid copolymer resin used in the film of the present invention contains 8 to 12% by weight of methacrylic acid. When the methacrylic acid content is less than 8% by weight, the transparency and elongation of the film are deteriorated, which is not preferable. On the other hand, when the content exceeds 12% by weight, shrink properties are not exhibited, and when the film is wrapped, wrinkles or looseness occur. It is not preferable because it occurs. The ethylene-methacrylic acid copolymer resin may be mixed with a desired additive or the like as necessary to form an intermediate layer.

The ethylene used in the film of the present invention
The vinyl acetate copolymer resin contains 3.5 to 30% by weight of vinyl acetate. When the content of this vinyl acetate is 3.5
When the content is less than 30% by weight, the transparency, elongation and self-adhesiveness of the film are deteriorated. On the other hand, when the content is more than 30% by weight, the blocking phenomenon between the films becomes large, and it becomes difficult to rewind the film. Absent. This ethylene-vinyl acetate copolymer resin has glycerin fatty acid ester type, sorbitan fatty acid ester type, polyglycerin fatty acid ester type, ethylene oxide adduct for the purpose of imparting antifogging property, antistatic property, and moderate slip property. A system surfactant can be added. Further, instead of the ethylene-vinyl acetate copolymer resin, an ethylene-ethyl acrylate copolymer resin and an ethylene-methyl methacrylate copolymer resin may be used.

The thickness of the intermediate layer constituting the film of the present invention is at least 30% of the thickness of the entire film layer, and the thickness of the ethylene-vinyl acetate copolymer resin layer laminated on both surfaces of the intermediate layer is at least 1 μm. Preferably, there is. If the thickness of the intermediate layer is less than 30% of the entire layer, bubble stability during stretching is deteriorated, and if the thickness of the resin layer is less than 1 μm, adhesiveness and transparency cannot be exhibited. Not preferred.

[0012] The configuration of the film as described above, Fi by melt co-extrusion inflation molding commonly known
But the blow ratio at this time must be 5 or more.
I have to. If the blow ratio is less than 5, it is difficult to impart heat shrinkage. Therefore, it is desirable to increase the blow ratio as much as possible to impart heat shrink characteristics.

The film of the present invention formed as described above has a heat shrinkage at 100 ° C. of 5% or more in the machine direction,
It is preferably 3% or more in the horizontal direction, and the heat shrinkage at 120 ° C. is preferably 20% or more in the vertical direction and 20% or more in the horizontal direction. The heat shrinkage at 100 ° C. is 5% in the vertical direction.
If it is less than 3% in the transverse direction, it generally dislikes high-temperature heating in the packaging process of food, and although heat shrinkage properties at as low a temperature as possible are required, the film at the time of heat shrinkage Since the shrinkage does not start unless the temperature is raised to the predetermined temperature, there is a drawback that high-temperature heating must be performed as a result.At a temperature lower than the predetermined temperature, the heat shrinkage becomes incomplete, wrinkles are generated, and the packaging finish is finished. It is not preferable because it does not become clean. When the heat shrinkage rate at 120 ° C. is less than 20% in the vertical direction and less than 20% in the horizontal direction, the packaging finish after the heat shrinkage is not beautifully finished, the film is weak in tension, and many wrinkles and looseness are generated. It is not preferable because it becomes a film.

In the film of the present invention, in addition to the above-mentioned range of the heat shrinkage, the stress at the time of 100% elongation is 55% in the longitudinal direction.
0 kgf / cm ² or less, lateral 350 kgf / cm ²
It is desirable that: This stress is 550K in the vertical direction
If it exceeds gf / cm ² and exceeds 350 kgf / cm ^{2 in the} lateral direction, a very large resistance occurs when performing stretch packaging, and a burden is placed on the arms and shoulders when packing by hand. Also, in the case of packaging with an automatic packaging machine, the range of adjustment of the machine for the package is narrowed, and it is necessary to perform the machine adjustment every time the size of the package is changed, which is not preferable because the operation becomes complicated.

[0015]

The film of the present invention has an intermediate layer of an ethylene-methacrylic acid copolymer resin having good heat shrinkage properties and excellent mechanical properties, and has an ethylene-vinyl acetate copolymer having excellent transparency and self-adhesiveness on both surfaces. Since the polymer resin layer is laminated, a non-PVC-based film having a wide range of applicability of the package to the film width and a small propagation to tear can be obtained.

[0016]

【Example】

(Example 1) An ethylene-methacrylic acid copolymer resin having a methacrylic acid content of 9% was used as an intermediate layer, and a resin obtained by adding a surfactant to an ethylene-acetic acid copolymer resin having a vinyl acetate content of 19% was used as an intermediate layer. And the thickness of all layers is 10 μm (7 μm for the intermediate layer, 3 μm for the other layers).
m), and a film was produced by inflation molding. The physical properties of the obtained film were measured by the following methods, and the results shown in Table 1 were obtained. As is clear from Table 1, the heat shrinkage and the stress at the time of 100% elongation sufficiently satisfied the present invention, and good results were obtained in all of the film formability, self-adhesiveness, and elastic recovery force.

Reference Example 1 A film was produced in the same manner as in Example 1 except that an ethylene-ethyl acrylate copolymer resin was used instead of the ethylene-acetic acid copolymer resin. The physical properties of the obtained film were measured by the following methods in the same manner as in Example 1, and the results shown in Table 1 were obtained.
As is clear from Table 1, the heat shrinkage and the stress at the time of 100% elongation sufficiently satisfied the present invention, and good results were obtained in all of the film formability, self-adhesiveness, and elastic recovery force.

Reference Example 2 A film was produced in the same manner as in Example 1 except that an ethylene-methyl methacrylate copolymer resin was used instead of the ethylene-acetic acid copolymer resin. The physical properties of the obtained film were measured by the following methods in the same manner as in Example 1, and the results shown in Table 1 were obtained. As is clear from Table 1, the heat shrinkage and the stress at the time of 100% elongation sufficiently satisfied the present invention, and good results were obtained in all of the film formability, self-adhesiveness, and elastic recovery force.

Comparative Example 1 A film was produced in the same manner as in Example 1 except that the methacrylic acid content of the ethylene-methacrylic acid copolymer resin was changed to 4%. The physical properties of the obtained film were measured by the following methods in the same manner as in Example 1, and the results shown in Table 1 were obtained. As is evident from Table 1, the heat shrinkage and the stress at the 100% elongation were sufficiently satisfied, but the use of food packaging was difficult due to the large Haze value.

Comparative Example 2 An ethylene-methacrylic acid copolymer resin having a methacrylic acid content of 4% was used as an intermediate layer, and a surfactant was added to an ethylene-vinyl acetate copolymer resin having a vinyl acetate content of 3%. A resin was provided on both surfaces of the intermediate layer, and a film was produced in the same manner as in Example 1 except for the above conditions.
The physical properties of the obtained film were measured by the following methods in the same manner as in Example 1, and the results shown in Table 1 were obtained. As is clear from Table 1, the heat shrinkage ratio was sufficiently satisfied, but was 100%.
It was difficult to use for food packaging due to high stress at elongation, high haze value, and lack of self-adhesion.

(Comparative Example 3) The content of methacrylic acid is 13%
The ethylene-methacrylic acid copolymer resin of Example 1 was used as an intermediate layer, and a resin obtained by adding a surfactant to an ethylene-acetic acid copolymer resin having a vinyl acetate content of 30% was provided on both surfaces of the intermediate layer. A film was produced as it was. The physical properties of the obtained film were measured by the following methods in the same manner as in Example 1, and the results shown in Table 1 were obtained. As is clear from Table 1, the film could not be obtained because the adhesiveness of the film surface during molding was too strong.

[0022]

[Table 1]

(Evaluation of Physical Properties) Transparency One film was measured by the test method according to JIS K-7105, and the Haze value was measured. 2. Antifogging property After 200 cc of hot water at 60 ° C. is put into a 500 cc beaker, the upper surface of the beaker is covered with a film, and the time required for the film to be free from fogging is measured.・ ・ ・: Film fogging disappeared in less than 10 seconds. Δ: The fogging of the film disappeared after 10 seconds or more, or the fogging did not disappear forever. 3. Self-adhesiveness Using Toyo Seiki Seisakusho Co., Ltd.'s “Heat gradient tester”, superimpose two films and set them in the test section.
The test was carried out under the condition of pressing at 1 ° C./cm ^{2 at} a pressure of 1 ° C. for 1 second, and it is preferable that the welded portion of the overlapped portion is sufficiently welded to be broken if it is forcibly peeled off.・ ・ ・: The two films are not easily peeled even when they are peeled. Δ: easily peels off when two films are peeled off. 4. Elastic recovery force Packaging is performed by an automatic packaging machine manufactured by Ibaraki Seiki Co., Ltd. A 30 g ball is placed on the center of the package for 10 seconds, removed, and the time until the wrinkles remaining on the film are removed is measured.・ ・ ・: Film wrinkles disappear in less than 6 seconds. Δ: Wrinkles disappear after 6 seconds or more, or wrinkles remain forever. 5. Stress at 100% Elongation Rate One film is measured by a test method according to JIS K-6732, and the stress when the interval between the marked lines is 100% is measured. 6. Heat shrinkage rate A film cut into a square of 10 cm in length and width is 10
Leave in an oven at 0 ° C and 120 ° C for 1 minute,
After being taken out, the length and length were measured and calculated by the following equation. Heat shrinkage rate = (10−A) / 100 × 100...% However, A is taken out and measured in length and width. Elongation of Film One film was measured by a test method according to JIS K-6732, and the elongation at break of the film was evaluated as the elongation of the film.

[0024]

According to the film of the present invention, since it has both a suitable shrink wrapping suitability and a stretch wrapping suitability, a practically highly desirable polyolefin-based film having a wide application range of the wrapping and a small propagation to the tear is provided. Can be provided.

Claims (1)

(57) [Claims] 1. An ethylene-vinyl acetate having a vinyl acetate content of 3.5 to 30% by weight is provided on both surfaces of an intermediate layer mainly containing an ethylene-methacrylic acid copolymer resin having a methacrylic acid content of 8 to 12% by weight. setting the resin composed mainly of a copolymer
A heat-shrinkable film for food packaging, wherein the heat-shrinkable film is formed by inflation molding with a blow ratio of 5 or more .