JPH0218328B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to an α-olefin copolymer () selected from ethylene-α-olefin copolymer or propylene-ethylene copolymer having a crystal melting point of 110 to 155°C, the α-olefin copolymer () and ethylene. A single-layer or laminated film having at least one layer consisting of a mixture of -vinyl acetate-copolymer (), and having a heat shrinkage rate at 90°C.
This relates to a heat shrinkable film having a shrinkage of 15% or more. Non-shrink and heat shrink packaging is used for packaging fatty foods such as raw meat, poultry, and processed meat. Non-shrink packaging is usually done by vacuum-packing foods, but when the shape of the food is irregular, meat juices tend to come out and the product shape is often damaged. Therefore, heat shrink packaging is generally the simplest method. In this case, when the food is packaged, it is recognized that the film softened by oil and heat may be stretched thin and torn, or may be torn at or near the sealing part. In addition, food packaging requires preservability, so gas barrier properties are generally required, but resins with gas barrier properties usually have poor cold resistance, so they are not necessarily suitable for short-term use. In many cases, it is not necessary to use a film with large gas barrier properties. As a conventional heat-shrinkable film with oil resistance, heat sealing resistance, and cold resistance,
Examples include a film made of polyethylene irradiated with radiation as described in Japanese Patent Publication No. 18893, and a film made of a propylene and ethylene copolymer described in Japanese Patent Publication No. 45-23437. Irradiation-irradiated polyethylene film requires equipment costs for the radiation irradiation equipment used to manufacture it, and requires complicated maintenance, management, and operation to ensure its safety. Propylene and ethylene copolymer films require high stretching temperatures, and it has been difficult to obtain films with a high heat shrinkage rate of 15% or more at 90°C. When low-density polyethylene with a crystal melting point of less than 110°C is used, the heat-resistant sealing properties are particularly insufficient.
When an α-olefin polymer with a crystal melting point of 110°C or higher is used, it has good heat sealing properties and oil resistance, but it has poor stretchability at a stretching temperature that would provide a heat shrinkage rate of 90°C. It has been difficult to obtain such a heat-shrinkable film. Therefore, there has been an extremely urgent need in the food packaging field to develop a heat-shrinkable film that requires relatively simple equipment and is particularly resistant to oil, heat sealing, and cold. The present invention overcomes the physical and equipment disadvantages of the conventional films described above, and makes it possible to obtain a film that has excellent oil resistance, heat sealability, and cold resistance, and has sufficient heat shrinkage at 90°C. The purpose of the present invention is to provide a heat-shrinkable film that can be stretched uniformly at a low stretching temperature. The heat shrinkable film of the present invention has a crystal melting point of 110 to 155.
20 to 60% by weight of an α-olefin copolymer () selected from ethylene-α-olefin copolymer or propylene-ethylene copolymer having a temperature of 20 to 60% by weight and ethylene-vinyl acetate copolymer (hereinafter abbreviated as EVA) () A laminated film having a single layer consisting of a mixture of 80 to 40% by weight or at least one layer consisting of the mixture, which is a heat-shrinkable film.
A heat-shrinkable film exhibiting a heat shrinkage rate of 15% or more at 90°C, characterized in that the weight ratio of EVA () is within the range of 0.4≦/+≦0.9. The structural feature of the present invention is that it is a single layer or a laminated film having at least one layer consisting of a specific ratio of α-olefin copolymer () having a specific crystal melting point and EVA (). It is.
Generally, α-olefin copolymer () alone, which has a high crystal melting point, has excellent heat sealing properties and oil resistance, but is poor in stretchability. Generally, for industrial heat shrink packaging, a film having a heat shrinkage rate of 15% or more at 90°C is desirable. On the other hand, in order to obtain a heat shrinkage rate of 15% or more at 90°C, it is necessary to lower the stretching temperature. Since α-olefin copolymer () alone has poor stretching properties, the stretching temperature cannot be lowered. In order to balance the physical contradictions of heat shrinkability, oil resistance, and heat sealability, the present inventors conducted intensive studies and developed an α-olefin copolymer (20 to 60% by weight) that is stretchable at low temperatures. It has been found that a film consisting of a mixture of 80-40% by weight of good EVA() is suitable. Furthermore, an α-olefin copolymer () layer or an EVA () layer can be laminated on the film, but in this case as well, the weight ratio of EVA () in all layers of the film is 0.4≦EVA()/α- Olefin copolymer () + EVA ()
It was found that it is necessary that ≦0.9. In this way, it was possible to obtain a packaging film with excellent heat shrinkability, oil resistance, and heat sealability. The present invention will be explained in detail below. The α-olefin copolymer () used in the present invention is an ethylene-
It is selected from one or more of α-olefin copolymers and propylene-ethylene copolymers. crystal melting point
The ethylene-α/olefin copolymer having a temperature of 110 to 155°C consists of ethylene, butene-1, pentene-1,
It is a copolymer with α-olefin having 18 or less carbon atoms, such as 4-methylpentene-1, hexene-1, and octene-1. The proportion of copolymerization is preferably 1.0 to 30% by weight of α-olefin. These polymers belong to a type of polyolefin, so-called linear density polyethylene (LLDPE), which is polymerized using transition metal-based catalysts. Commercial products of the copolymer used in the present invention include, for example, Urtozex, Neozex (all products of Mitsui Petrochemicals), and Dowrex (products of Dow Chemical). As the propylene-ethylene copolymer having a crystal melting point of 110 to 155°C, a copolymer having an ethylene content of 1 to 7% by weight is preferably used. As the EVA () to be mixed with the above α-olefin copolymer (), one having a crystal melting point of 80 to 103°C is used. Among these, the most preferable for heat-resistant sealing properties are those with a melt index of 0.2 to 4.0 (g/10 minutes) and a vinyl acetate content of 3 to 12% by weight in EVA, as shown in the figure, U, V, W. ,
This is within the polygon enclosed by the X, Y, and Z points. The figure shows the vinyl acetate content (wt%) in EVA on the horizontal axis, and the melt index (g/10
FIG. 2 is a diagram showing the relationship between vinyl acetate content and melt index when the vertical axis is 0.5 min). In the figure, the point U where the vinyl acetate content is 3% and the melt index is 0.2 is represented by U (3, 0.2). Therefore, this polygon is U (3, 0.2), V (12, 0.2), W (12, 0.5)
,
It is a connection of X (9, 0.5), Y (5, 4.0), and Z (3, 4.0). The melt index of the polymer is ASTM D-
Measured using methods such as 1238. The crystal melting point can also be measured using a differential scanning calorimeter (PerkinElmer IB).
The temperature that showed the maximum value of the obtained melting curve was adopted. The mixing ratio of α-olefin copolymer () and EVA () is 20 to 60% of α-olefin copolymer ()
It is necessary that the weight% and EVA () are 80-40% by weight. If the α-olefin copolymer () content is less than 20% by weight, stretchability is excellent, but oil resistance and heat-resistant sealability are poor. Moreover, if it exceeds 60% by weight, the stretchability becomes poor and the object of the present invention cannot be achieved. In the heat-shrinkable film of the present invention, the α-olefin copolymer () mixed in the above ratio and
When the layers made of EVA () constitute two or more layers, the two copolymers may be mixed in the same ratio or in different ratios in each laminated layer. Furthermore, the heat-shrinkable film of the present invention includes one or more of the above layers made of α-olefin copolymer () and EVA (), and a layer made of α-olefin copolymer (), EVA (), or a mixture thereof. This includes laminated films having at least one layer of. The thickness and number of layers of each layer can be changed freely, but the weight ratio of EVA () in all layers of the film is 0.4≦ EVA () / α-olefin copolymer () + EVA ()
Must be ≦0.9. Outside this range, stretchability, oil resistance, and heat sealability cannot be satisfied, and the object of the present invention cannot be achieved. In the case of lamination, since the adhesion between each layer is sufficient, there is no need to use an adhesive, although an adhesive layer may of course be provided. In the present invention, the thickness of the entire layer is not limited depending on the contents to be packaged, but it is generally and preferably 20 to 120 microns. In addition, in the case of laminated film,
As mentioned earlier, the thickness of each layer can be changed freely as long as the ratio of α-olefin copolymer () and EVA ( It is preferable that the layer consisting of a mixture of ) has a thickness of at least 20% of the total thickness. This is because when this layer is used as a sealing layer, if the thickness is less than 20%, problems may occur in heat-resistant sealing properties. When implementing the present invention, if a laminated structure is adopted,
The outermost layer is α-olefin-copolymer () and
Can be a mixture of EVA (), oil resistant,
From the point of view of heat-resistant sealability, EVA layer () layer and α・
It is not preferable to use a layer of a mixture containing less than 20% of the olefin polymer () as the outer layer. Therefore EVA
The layer ( ) and the layer containing a mixture containing less than 20% α-olefin polymer are always used as inner layers and are never used as outer layers. Therefore, in the case of two layers, these layers are not used, but in the case of three or more layers, they are used. Furthermore, when the film is applied to a packaging machine, it is necessary to use a film that does not have curling properties, and it is known that for this purpose, it is easier to adjust the curling property of a laminated film. Therefore, industrially, it is more advantageous to use a laminated film. The film of the present invention can be produced by a generally known method. That is, using an extruder according to the number of layers, cylindrical ones are extruded into a cylindrical shape using a known annular die, and flat ones are extruded into a flat shape using a known T die. be done. The cylindrical extrudate is once rapidly cooled at a temperature of 0 to 25°C immediately below the die, then folded, heated to a constant temperature, and then biaxially stretched to obtain a heat-shrinkable cylindrical film. Further, the planar laminate is once cooled by a chill roll immediately below the die, heated to a constant temperature, and then biaxially stretched to obtain a heat-shrinkable film. The heat-shrinkable film obtained by the present invention has excellent oil resistance, heat sealability, and cold resistance, so
Used for packaging various foods. It has been particularly suitably used for packaging fatty foods that require high-temperature sterilization or frozen transportation, and excellent results have been obtained. 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. EXAMPLE Resins consisting of the polymers listed in Table 1 were extruded separately using extruders depending on the number of layers, and the molten materials were flowed into a coextrusion annular die to form a desired cylindrical product. The cylindrical material discharged from the die was cooled in a cooling tank at 15 to 25°C to form a cylindrical product with a flat width of 120 mm and a thickness of 100 to 400 μm. Soybean oil was sealed in the cylindrical body in the cooling tank to prevent the inner peripheries from adhering to each other. Next, the cylindrical body was heated for about 12 seconds while being fed at a speed of 5 m/min in a hot water bath or oven adjusted to the stretching temperature shown in Table 2.
It was passed through a first nip roller with a rotational speed of m/min. The cylindrical body is cooled in a room temperature atmosphere and is
By the time it passes through the second nip roller, which rotates every minute, it is stretched twice in the longitudinal direction, and expanded and stretched twice in the transverse direction with respect to the diameter of the cylinder by the air sent into the cylinder. . The resulting biaxially stretched film had a fold diameter of about 360 mm and a thickness of about 25 to 100 μm. Table 1 shows the physical properties of the polymers used in the examples.
Table 3 shows the layer structure of the films obtained in Examples, the results of physical property tests of the films, and Table 3 shows the methods of testing the physical properties of the films obtained.

[Table] *2 Product name Neoxex (same as above)
*3 Product name: Noblen (manufactured by Sumitomo Chemical)

【table】

【table】

[Table] As is clear from Examples 1 to 8 in Table 2, the films of the present invention all have excellent stretchability, sufficient heat shrinkage at 90°C, and excellent oil resistance, heat resistance, and cold resistance. was gotten. On the other hand, although Comparative Example 1 was a mixture of propylene-ethylene copolymer and EVA, the EVA content was as low as 20%, requiring high-temperature stretching, and the heat shrinkage rate was insufficient. Comparative Examples 2 and 3 were laminated films, but the amount of EVA () in all layers exceeded 90%, so the oil resistance and heat-resistant sealability were insufficient.

[Brief explanation of drawings]

The drawings show ethylene which is preferably used in the present invention.
It shows the relationship between the melt index (vertical axis) and the vinyl acetate content (horizontal axis) of a vinyl acetate copolymer.

Claims (1)

[Claims] 1. Ethylene-α having a crystal melting point of 110 to 155°C
α-olefin copolymer (20 to 60% by weight) selected from olefin copolymers and propylene-ethylene copolymers, and ethylene-vinyl acetate copolymer (20 to 40%) having a crystal melting point of 80 to 103°C % by weight, and the copolymer () in a heat-shrinkable film has at least one layer consisting of a mixture of
The heat shrinkage rate at 90℃ is 15, characterized by the content ratio of 0.4≦/+≦0.9 within the range of the general formula below.
% or more single layer or laminated heat shrinkable film. 2. Claims in which the ethylene-α-olefin copolymer is a copolymer of ethylene and an α-olefin selected from 1-butene, 1-pentene, 1-4-methylpentene, 1-hexene, and 1-octene. 2. The heat-shrinkable film according to item 1. 3 Propylene-ethylene copolymer is ethylene-
The heat-shrinkable film according to claim 1, which is a copolymer containing 1 to 7% by weight. 4 In a diagram in which ethylene-vinyl acetate copolymer () has vinyl acetate content (wt%) on the horizontal axis and melt index (g/10 min) on the vertical axis, U (3,
0.2), V (12, 0.2), W (12, 0.5), X (9, 0.5)
,
The heat-shrinkable film according to claim 1, which is selected from within the polygon formed by connecting Y (5, 4.0) and Z (3, 4.0).