JPH0486259A - Film for packaging - Google Patents

Abstract

PURPOSE:To manufacture a film for packaging of superior cutting properties, transparency, resistance to heat, water vapor barrier properties by co-extrusion molding respective resin having an intermediate layer of aliphatic polyamide resin between both surface layers formed of an outer layer and an inner layer of polypropylene family resin, and then setting the thickness of whole film drawn with a specified expansion rate in the take-off direction of film at a specified value and the thickness of intermediate film within a specified range of the thickness of whole film. CONSTITUTION:An outer layer and an inner layer are composed of a polypropylene family resin propylene single polymer or the like. On the other hand, nylon - 6, a nylon - 6/6.6 copolymer or the like is used as an example for resin family polyamide constituting an intermediate layer of a film for packaging. For instance, a multi-layer film of (polypropylene family resin/aliphatic polyamide resin/polypropylene family resin) is formed by the two kind three layer constitution by means of the specified co-extrusion using propylene family resin and aliphatic polyamide resin, and then said film is uniaxially drawn in the take-off direction of the film with drawing rate of 2-4.5 times. The thickness is 40mum or less, and the thickness of the intermediate layer is in the range of 10-90% to the thickness of the whole film.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a packaging film used for food packaging and the like. Specifically, the present invention has excellent cutability, transparency, heat resistance,
The present invention relates to a stretched laminated film suitable for use as a packaging film having excellent water-to-air barrier properties, non-heat shrinkability, and food safety.

[Conventional technology]

BACKGROUND ART Conventionally, wrap films used for food packaging are known that are mainly made of polyvinylidene chloride, polyethylene, or polyvinyl chloride.

[Problem to be solved by the invention]

However, polyvinylidene chloride-based films have the disadvantage of large shrinkage when heated, and polyethylene-based films may melt if they come into contact with oily objects (e.g., meat, tempura, etc.) and are exposed to high heat. Furthermore, polyvinyl chloride films have the problem of whitening when they come into contact with boiling water.

On the other hand, aliphatic polyamide resins are known as heat-resistant resins that can be used as packaging films.

Although aliphatic polyamide resin has excellent heat resistance and mechanical strength, it is difficult to maintain its original physical properties because of its high hygroscopicity. Especially nylon-〇 and nylon-6
Copolymerized nylons such as /6,6 and nylon-6/6゜10 are restricted from being used in food packaging applications due to food safety concerns, as their monomer component ε-caprolactam bleeds onto the film surface. has been done.

Furthermore, such wrapping films have the following problems in terms of cuttability (ease of cutting). In other words, wrapping film is usually stored in a case such as a paper tube.
The film is pulled out by applying it to a cutting blade called a ``saw blade'' attached to this case and cut into an appropriate length.

The ``saw blade'' used to cut the film is generally a simple blade made by punching a saw-shaped iron plate approximately 0.2 mm thick. As for the supporting case, a paper box made of coated cardboard with a weight of about 350 to 700 g/po is used, and its rigidity is extremely low.

This type of film is required to be easily cut according to the user's will even with such a simple cutting mechanism, but in reality, the case and the "saw blade" are often deformed. Otherwise, the film may be deformed or
Cutting may occur at a position that is outside the saw blade. Specifically, when conventional polyvinylidene chloride film is cut, if a tear forms in a part of the film, the tear spreads and the film is cut along the "saw blade". There is a tendency to cut diagonally without cutting. In addition, conventional polyethylene films require considerable tensile force when cut, which not only causes the case to bend, but also
The film may become deformed.

[Means to solve the problem]

As a result of extensive research in order to produce a packaging film that solves the above-mentioned problems of conventional wrapping films, the inventors of the present invention have laminated polypropylene resin on both sides of an aliphatic polyamide resin using a specific coextrusion method. By stretching the material in the direction in which the film is taken, the above problems are resolved and the inherent properties of polyamide resin (heat resistance and mechanical strength) are improved.
The present invention was achieved by discovering that it is possible to obtain a packaging film that has excellent heat resistance, water vapor barrier properties, non-heat shrinkability, and food safety without impairing the properties of the packaging material.

That is, the gist of the present invention is a multilayer film having an outer layer and an inner layer each made of a polypropylene resin, each of which constitutes both surface layers, and an intermediate layer made of an aliphatic polyamide resin between the two surface layers. It is obtained by coextrusion molding by T-die molding method or water-cooled inflation molding method, and then stretching at a stretching ratio of 2 to 4.5 times in the drawing direction of the film, and the total thickness of the film is 40 μm.
or less, and the thickness of the intermediate layer is in the range of 10 to 90% of the thickness of the entire film.

Hereinafter, the present invention will be explained in detail.

The packaging film of the present invention has a layer structure of at least three layers including both outer and inner layers and an intermediate layer therebetween, for example, a 3' layer consisting of outer layer/intermediate layer/inner layer.

The type of polypropylene resin constituting the outer layer and inner layer of the packaging film is not particularly limited, and may be a propylene homopolymer or a copolymer of ethylene or the like and propylene. Examples of the propylene homopolymer include isotactic polypropylene, syndioctic polypropylene, and acidic polypropylene, and isotactic polypropylene is particularly preferred. Furthermore, the copolymer of propylene and other components such as ethylene may be either a random copolymer or a block copolymer. Note that the physical properties of this polypropylene resin may be selected depending on various uses, conditions, etc., but usually,
Melt flow rate (MFR) 0.5-10 g/l
0 minutes and a density of 0.89 to 0.91 g/crR1 are preferred. Melt flow rate is JIS K67
58, measured at 230°C and 16kg load.

On the other hand, examples of the aliphatic polyamide constituting the intermediate layer of the packaging film of the present invention include nylon-6, nylon-6,
6, nylon-6,10, nylon-6/6.6 copolymer, nylon-6/610 copolymer, and the like.

The packaging film of the present invention has a two-layer, three-layer structure, for example, a multilayer structure of [polypropylene resin/aliphatic polyamide resin/polypropylene resin] by coextrusion molding of the above-mentioned polypropylene resin and aliphatic polyamide resin in a specific manner. The film is formed by forming the film and then axially stretching the film in the drawing direction (longitudinal direction).

As the coextrusion molding, a T-die molding method or a water-cooled inflation molding method is adopted. That is, by rapidly cooling the melt-extruded resin using the second molding method, a film with better transparency can be obtained compared to the commonly used air-cooled inflation molding method.

The unstretched multilayer film obtained by the above coextrusion molding is
Then, the film is stretched at a stretching ratio of 2 to 4 in the direction of take-up (vertical direction).
．． Axial stretching is carried out 5 times, preferably 2.5 to 4 times. If the stretching ratio is less than 2 times, the film will have insufficient curling properties, and if it is more than 4 or 5 times, the stretching property will decrease, resulting in breakage or uneven stretching of the film, which is not desirable. The stretching treatment is carried out by heating the above-mentioned unstretched film as it is or after slitting it to a predetermined width, and stretching the film in the longitudinal direction by changing the circumferential speed of a stretching roll, for example. .

The preheating temperature in the stretching process is usually below [the melting point of the polypropylene resin -20°C], preferably 40°C.
It is preferable to carry out the reaction at a temperature in the range of 120°C to 120°C.

In addition, the heat setting temperature after stretching should be higher than the preheating temperature, and in order to prevent wrinkles and improve the transverse strength of the film,
The temperature is preferably as high as possible, usually below [the melting point of the polypropylene resin, 20°C], preferably in the range of 80 to 150°C.

If the preheating and heat setting temperature is higher than [the melting point of polypropylene resin -20°C], the film will melt and adhere to the stretching roll, and if the preheating temperature is less than 40°C, the aliphatic polyamide resin will not be preheated. This is not desirable because the film becomes difficult to stretch and the film breaks.

The thickness of the packaging film of the present invention is 40 μm or less,
Preferably 2 to 30 μm, more preferably 5 to 20 μm
The thickness of the intermediate layer is in the range of 10 to 90% of the total thickness of the film. If the thickness of the film is greater than 40 μm, the tear strength upon cutting the film will be too high, making it unsuitable for use as a wrap film.

If the thickness of the intermediate layer is less than 10% of the total thickness, it will not be possible to maintain the heat resistance, mechanical strength, etc. inherent to the polyamide resin, and the physical properties of an axially stretched polypropylene film will become dominant. It is easy to tear. The thickness of the intermediate layer is preferably 15% or more of the total thickness.

On the other hand, if it is larger than 90%, the thickness of the polypropylene layer becomes thin, making it difficult to uniformly cover the intermediate layer by coextrusion molding. The thickness of the intermediate layer is preferably 80% or less of the total thickness.

The packaging film of the present invention is used for various packaging applications such as food packaging. Further, by imparting self-adhesive properties to the outer layer and inner layer constituting both surface layers by an appropriate method, it can be suitably used as a wrap film.

〔Example〕

Hereinafter, specific embodiments of the present invention will be explained in more detail with reference to Examples, but the present invention is not limited by these Examples unless the gist thereof is exceeded.

Measurements in the examples were performed using the following method.

(1) Moisture permeability Measured according to JIS 20208 at 40°C and 190%RH.

(2) Transparency (haze value) Measured using a haze meter in accordance with JIS K-6714.

(3) A strip of film with a heat resistance temperature width of 30 mm and a length of 14 cm. Place paper 25 mm above and below the sample piece to lower the Log weight. The maximum atmospheric temperature that did not break in one hour was measured in 10°C increments.

(4) Heat shrinkage rate Make a sample of Fill J with a diameter of 10 mm using a punching jig, immerse it in an aluminum pan containing silicone oil,
Place this aluminum pan on a hot plate at 140°C. Because the heat is taken away by the aluminum pan, pot play 1.
temperature decreases, but after reaching 140°C
After 5 seconds, the sample is removed and its size change is measured.

(5) Wrap the cuttable film around the core tube, store it in a wrap film case, and perform a cutting test with a saw blade.
Good, fair, slightly poor, poor) were evaluated. As an evaluation standard, the cut level of a commercially available wrap film was evaluated as normal.

Example 1 Using a 450 mm width 3 types 3 layer coextrusion T-die molding machine Table 1
The resin shown in is simultaneously extruded from three extruders at a die temperature of 280°C, a chill roll temperature of 30°C, a take-up speed of 20
The film was formed under conditions of m/min, outer layer (polypropylene)/intermediate layer (nylon-6/6.6)/inner layer (polypropylene).
Two types of three-layer film (thickness: 30 μm, layer ratio: 1:2)
:1) was molded. The film was then stretched 3.6 times in the machine direction by roll stretching at a preheating temperature of 60°C and a heat setting temperature of 110'C. The obtained film was evaluated for moisture permeability, transparency, heat resistance, heat shrinkage rate, and cuttability using the above methods. The results are shown in Table 2.

Example 2 The same procedure as in Example 1 was carried out except that the ratio of each layer of the multilayer film was 2:1:2. The results are shown in Table 2.

Example 3 Example 1 was carried out in the same manner as in Example 1 except that water-cooled inflation molding was used for forming the original fabric. The results are shown in Table 2. The original fabric forming conditions are a die diameter of 75 mm.
φ, die temperature 250°C, blowup ratio 1.8. The take-up speed is 17 m/min, and the folding width is 210 mm.
, a film with a thickness of 30 μm was molded.

Comparative Examples 1 to 5 Comparative Examples 1 to 5 were carried out in the same manner as in Example 1 except that the film thickness, film layer ratio, and stretching ratio were as shown in Table 2. The results are shown in Table 2.

Comparative Example 6 The same procedure as in Example 1 was carried out except that the original fabric was formed by air-cooled inflation molding.

The results are shown in Table 2. The original fabric forming conditions were a die diameter of 100 mtnφ, a die temperature of 250°C, and a flow-up ratio of 1.8. A film having a fold width of 280 mm and a thickness of 30 μm was formed at a take-up speed of 23 m/min.

Table 1 Note) Polypropylene (propylene-ethylene random copolymer) Mitsubishi Polypro 6500J manufactured by Mitsubishi Chemical Corporation Nylon-6/6.6 Tsubamitsudo ■2030 manufactured by Mitsubishi Chemical Corporation [Effects of the invention] The packaging film of the present invention has excellent cutability. , has excellent transparency, heat resistance, water vapor barrier properties, and non-heat shrinkability, and is a raw material monomer for nylon-6 and its copolymerized nylon.
- In order to suppress the bleeding of caprolactam onto the film surface by laminating polypropylene resin,
It also has excellent food safety.

Claims (1)

[Claims] (1) A multilayer film in which an outer layer and an inner layer each made of a polypropylene resin constitute both surface layers, and an intermediate layer made of an aliphatic polyamide resin is formed between the two surface layers, and each of the above resins is formed by T-die molding. The film is obtained by coextrusion molding by a method or water-cooled inflation molding method, and then stretching at a stretching ratio of 2 to 4.5 times in the drawing direction of the film, and the total thickness of the film is 40 μm or less, and The thickness of the above-mentioned intermediate layer is 10 to 9 times the thickness of the entire film.
A packaging film characterized in that the content is in the range of 0%.