JPS625792B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention uses a gas barrier polymer as a core layer and heats the temperature at 115°C.
At least an ethylene and α-olefin copolymer having a crystal melting point of ~130°C or the copolymer
It relates to a heat-shrinkable laminated film comprising an outer layer (A) containing 20% by weight, an outer layer (B) made of an ionomer resin, and an adhesive layer between the core layer and the outer layer (A) and the outer layer (B). Heat shrink packaging is industrially the simplest method for packaging foods with irregular shapes such as raw meat, processed meat, cheese, and other fatty foods.
Furthermore, since these packages are required to have a long shelf life, they must have gas barrier properties. Furthermore, when packaging fatty foods, the film softened by oil and heat is stretched thin, causing the problem that only the outer layer is torn, so a film with excellent oil resistance is desired. Vinylidene chloride copolymer (hereinafter referred to as PVDC) is a heat-shrinkable film with gas barrier properties.
Single film, ethylene-vinyl acetate copolymer (hereinafter referred to as EVA) in Canadian Patent No. 982923
and PVDC laminated film (hereinafter referred to as EVA/PVDC/
(referred to as EVA film), published in Japanese Patent Application Laid-open No. 1973-34565.
Irradiated laminated film of EVA, PVDC, and irradiated EVA, Irradiated laminated film using ethylene-vinyl alcohol copolymer (hereinafter referred to as Et-OH) instead of PVDC, polyethylene with a relatively low crystal melting point, EVA, ethylene There is a laminated film (Japanese Patent Laid-Open No. 82888/1988) made of a resin selected from copolymers, PVDC, and an ionomer resin. Depending on the type of food being packaged, additives such as plasticizers and stabilizers may migrate into the food, which is undesirable from a hygienic standpoint. Since it is contained in a large amount, there are disadvantages such as a decrease in gas barrier properties and an unfavorable state for food storage. EVA/PVDC/EVA laminated film has EVA in its outer layer, which has good cold resistance, so it requires only a small amount of additives.
Although it can compensate for the drawbacks of PVDC alone, EVA has poor oil resistance. Radiation crosslinking to improve oil resistance of EVA
In the method using EVA, crosslinking of both outer layers is not carried out because it would cause decomposition of PVDC or Et-OH in the core layer. Therefore, during the packaging process of resinous foods, it is inevitable that fat or oil will adhere to the uncrosslinked layer, resulting in insufficient oil resistance. Japanese Unexamined Patent Publication 1973-
No. 82888 is a cylindrical laminated film that has good stretchability, good productivity, and heat resistance.However, recently packaged foods are often heated at high temperatures for a longer time than before to sterilize them, and in this case, one side Since the outer layer is made of EVA, polyethylene, etc., which have a relatively low crystal melting point, when fat or oil adheres to this layer, the oil resistance may be insufficient. On the other hand, when ionomer resin/PVDC/ionomer resin is heat-shrinked or heat-sterilized in a hot water bath, the ionomer resin film that comes into contact with hot water becomes cloudy, and when heated and stretched in a hot water bath, water droplets may form. The so-called water rising phenomenon that causes spots may occur, resulting in a poor appearance. The present inventors have succeeded in developing a heat-shrinkable film that improves these points and has excellent oil resistance and gas barrier properties and can be stretched uniformly. That is, in the present invention, the core layer is made of vinylidene chloride copolymer or ethylene-vinyl alcohol copolymer, and the outer layer (A) has a specific gravity of 0.900 to 0.950 and a crystal melting point of 115.
Ethylene and α-olefin copolymer having 4 to 18 carbon atoms () having a temperature of ~130°C or 20% by weight or more of said copolymer () and an ethylene-vinyl acetate copolymer having a crystal melting point of 80 to 103°C ( ) 80% by weight or less, the other outer layer (B) is an ionomer resin, and is characterized by having an adhesive layer between the core layer and the outer layer. Since the outer layer (A) of the present invention is made of an ethylene-α-olefin copolymer having a high crystal melting point or a mixture of the ethylene-α-olefin copolymer and EVA, it has excellent heat resistance and oil resistance, and has a crystal melting point. Although it contains a high resin content, it has good stretchability. On the other hand, the outer layer (B)
Because it uses ionomer resin, it has good heat resistance, oil resistance, and stretchability. Generally, the outer layer (B) is used on the side that comes into direct contact with food, and the outer layer (A) is used facing the hot water bath side, but since the outer layer (A) has the above-mentioned structure, it does not cause cloudiness or water rising. will not occur. In the present invention, it has a crystal melting point of 115 to 130 °C,
Ethylene and butene copolymers () exhibiting a specific gravity of 0.900 to 0.950 are
1. Pentene Copolymers with α-olefins having 4 to 18 carbon atoms, such as 1,4-methylpentene-1, hexene-1, and octene-1, are used. The amount of α-olefin bound in the copolymer ranges from 1.0 to 30% by weight. These copolymers are so-called polymerized using transition metal-based catalysts.
It belongs to a type of polyolefin called LLDPE. The copolymers used in the present invention are those mentioned above, and commercially available products include, for example, Urtozex, Neozex, (all manufactured by Mitsui Petrochemical), G Resin (manufactured by Union Carbide), and Dowrex (manufactured by Dow Chemical). . EVA () mixed with the above ethylene and α-olefin copolymer () used for the outer layer (A)
As such, those having a crystalline melting point of 80 to 103°C are used. The crystalline melting point of the polymer is the temperature at which the maximum value of the melting curve obtained is measured using a differential scanning calorimeter (Model IB manufactured by PerkinElmer) using a sample of 8 mg at a heating rate of 8° C./min. What is PVDC used for the core layer in the present invention?65
~95% by weight of vinylidene chloride and at least one unsaturated monomer copolymerizable with it 5-35
It is a copolymer consisting of % by weight. Examples of copolymerizable unsaturated monomers include vinyl chloride, acrylonitrile, and acrylic acid alkyl esters (alkyl group having 1 to 18 carbon atoms). Among these, vinylidene chloride-vinyl chloride copolymer is common. Known plasticizers, stabilizers, etc. can be added to this vinylidene chloride resin as necessary. Further, Et-OH is a resin obtained by partially saponifying an ethylene and vinyl acetate copolymer, and a resin having an ethylene content of 20 to 80 mol% and a degree of saponification of 50 mol% or more is used. The ionomer resin used for the outer layer (B) is a copolymer of α-olefin such as ethylene or propylene and an unsaturated carboxylic acid such ^as acrylic acid, methacrylic acid, or maleic acid ^. ,
It is an ionic crosslinked product that is neutralized with metal ions such as Mg ⁺⁺ , Ca ⁺⁺ , Zn ⁺⁺ , etc. Since these polymers and PVDC are inherently incompatible, their laminates tend to peel off. In particular, the field of application of the film of the present application often requires immersion in hot water for shrinkage or sterilization, so weak adhesion will cause peeling and poor appearance. Therefore, in the present application, it is necessary to provide a strong adhesive layer at the interface between the outer layer and the core layer to prevent layer peeling. For the adhesive layer, carboxylic acid-modified polyolefin, ethylene-vinyl acetate copolymer, styrene-butadiene block copolymer, etc. are used. Especially when the core layer is PVDC, ethylene with a vinyl acetate content of 13 to 25% by weight is used.
A vinyl acetate copolymer or an ethylene-vinyl acetate copolymer mixed with these so as to have a vinyl acetate content is preferable, and when the core layer is Et-OH, an ethylene-vinyl acetate copolymer with a vinyl acetate content of 8 to 20% by weight is preferable.
A vinyl acetate copolymer or an ethylene-vinyl acetate copolymer mixture mixed to have the same vinyl acetate content is preferred. The total thickness is preferably about 20 to 120μ,
The outer layer (A) needs to have a thickness of 18% or more of the total layer thickness for heat resistance and oil resistance. The laminated film of the present invention is extruded into a cylindrical shape using an extruder according to the number of laminated layers, and a cylindrical one is extruded into a cylindrical shape using an annular die similar to that of JP-A-53-82888. Using a known T-die, it is extruded into a flat shape and laminated. After the cylindrical laminate is once rapidly cooled directly under the die,
After being folded with a nip roller and heated in a hot water bath and/or oven heated to a constant temperature, it is stretched in the longitudinal and diametrical directions by simultaneous biaxial inflation to obtain a heat-shrinkable cylindrical film. In addition, the planar laminate is first cooled by chill rolls directly below the die, then heated to a constant temperature, stretched in the machine direction between rolls, and then stretched in the width direction with a tenter, or sequentially biaxially stretched. 2 at the same time in both the flow direction and the width direction.
A heat-shrinkable film is obtained by stretching in the axial direction. This heat-shrinkable stretched film obtained by the present invention has excellent heat resistance and gas barrier properties,
Particularly suitable for packaging fatty foods. Examples will be described below, but the present invention is not limited to these examples as long as it is within the scope of the claims. EXAMPLES A resin consisting of the polymers listed in Table 1 is extruded separately in a plurality of extruders, and the molten materials are coextruded and flowed into an annular die where they are formed into the desired laminate. The cylindrical body of the laminate flowing out from the die is 15~
Cooled in a 25℃ cooling tank, flat width 120mm, thickness 600μ
It becomes cylindrical. Soybean oil is sealed inside the cylindrical body in the cooling tank to prevent the inner surfaces from sticking to each other. Next, so that the stretching temperature is as shown in Table 2,
The cylindrical body is heated for about 12 seconds while being fed through a controlled hot water bath at a speed of 5 m/min, and passed through a first nip roller at a rotational speed of 5 m/min. The cylindrical body is cooled in a room temperature atmosphere until it passes the second nip roller that rotates at 15 m/min.
While being stretched 3.2 times in the longitudinal direction, air sent into the cylindrical body expanded it to 3.2 times the diameter of the cylindrical body and stretched in the transverse direction. The resulting biaxially stretched film had a fold diameter of about 360 mm and a thickness of about 60 μm. Table 1 shows the physical properties of the polymers used in the examples.
Table 2 shows the layer structure of the laminated film obtained in the example, Table 3 shows the method of testing the physical properties of the film obtained,
Table 4 shows the physical property test results of the film.

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[Table] As is clear from Examples 1 to 8, the laminated films of the present invention all exhibit excellent shrinkability, oil resistance, and gas barrier properties. In addition, no deterioration of the oil resistance of the outer layer (B) was observed after 10 minutes. In Comparative Example 1, since low density polyethylene was used for the outer layer (A), there was no deterioration within 3 seconds, but deterioration was observed within 3 minutes. Comparative Example 2 used a mixture of low density polyethylene and EVA, and Comparative Examples 3 and 4 both used EVA for the outer layer (A), but the oil resistance was poor.

Claims (1)

[Claims] 1 The core layer is vinylidene chloride copolymer or ethylene-vinyl alcohol copolymer, and the outer layer (A) is a copolymer of ethylene and α-olefin having 4 to 18 carbon atoms and having a specific gravity of 0.900 to 0.950 and a crystal melting point of 115 to 130°C. It consists of a mixture of 20% by weight or more of the copolymer () or the copolymer () and 80% by weight or less of an ethylene-vinyl acetate copolymer () having a crystal melting point of 80-103°C, and the thickness of the layer is equal to or less than that of the entire layer. Excellent gas barrier properties and oil resistance, characterized by having a thickness of 18% or more, the other outer layer (B) is an ionomer resin, and an adhesive layer between the core layer and the outer layer. heat shrinkable film.