JPH0217350B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to vinylidene chloride copolymer (hereinafter referred to as
(referred to as PVDC) as the core layer, one outer layer is a mixture of propylene-ethylene copolymer and ethylene-vinyl acetate copolymer (hereinafter referred to as EVA), and the other outer layer is a propylene-ethylene copolymer or ethylene-vinyl acetate copolymer (hereinafter referred to as EVA). It is made of a mixture of α-olefin copolymer and EVA, and has an adhesive layer between the core layer and each outer layer, and is a replacement for the heat-shrinkable laminated film that has excellent oil resistance, heat-resistant sealing properties, and gas barrier properties. . Industrially, heat shrink packaging is 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, packaging for processed meat requires heat to be applied for a certain period of time to sterilize it (for example, at 90°C for at least 8 minutes in the case of E. coli), so oil resistance and heat-resistant sealability are required. In other words, when packaging and sterilizing fatty foods, the film softened by oil and heat is stretched thin and only the outer layer is torn, or the heat shrinkage stress generated during heat shrinkage and sterilization places a load on the sealing part, causing the seal to fail. Therefore, there is a need for a film that has excellent oil resistance and heat sealing properties. As a heat-shrinkable film with gas barrier properties,
PVDC single film, ethylene-vinyl acetate copolymer (hereinafter referred to as EVA) and PVDC laminated film (hereinafter referred to as EVM/
(referred to as PVDC/EVA film), Japanese Patent Application Publication No. 1973-
Irradiated with EVA and PVDC in 34565
There are EVA cylindrical laminated films, etc. Depending on the type of food being packaged, PVDC-only film may migrate into the food with additives such as plasticizers and stabilizers, which may be unfavorable from a hygienic standpoint, or require a relatively large amount of additives to maintain cold resistance. There are drawbacks such as a decrease in gas barrier properties due to the inclusion of the chlorine in the food, resulting in an unfavorable state for food storage. EVM/PVDC/EVA laminated film uses EVA as the 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 oil resistance,
Poor heat sealing properties. Even in JP-A No. 47-34565, which uses radiation-crosslinked EVA to improve the oil resistance of EVA, crosslinking of both outer layers is not carried out because it causes decomposition of the PVDC in the core layer. Furthermore, heat-resistant sealability does not improve even if EVA is cross-linked by radiation. Further, when low density polyethylene or ionomer resin having a crystal melting point of less than 110° C. is used for both outer layers, the heat-resistant sealability is particularly insufficient. In addition, when a polymer with a high crystal melting point is used, heat sealing properties and oil resistance are improved, but these polymers have poor stretchability and are not suitable for PVDC.
It cannot be easily and uniformly stretched because it is laminated with layers.
It was difficult to obtain a heat-shrinkable film. Therefore, there has been an extremely urgent need in the food packaging field for the development of a heat-shrinkable laminated film that has oil resistance, heat-resistant sealing properties, and good gas barrier properties. The present invention will be explained in detail below. The propylene-ethylene copolymer () having a crystalline melting point of 130 DEG to 155 DEG C. used in the outer layer of the present invention preferably has an ethylene content of 1 to 7% by weight and has excellent heat resistance and oil resistance. The propylene-ethylene copolymer () is used in at least one layer, and may of course be used in both outer layers. 110℃～
Ethylene-α/olefin copolymer (), which has a crystalline melting point of 125°C, is also a heat-resistant resin, and is a resin with ethylene, butene-1, pentene-1, 4-methyl pentene-1, hexene-1, octene-1.
It is a copolymer having 18 or less carbon atoms, such as 1. The proportion of copolymerization is usually in the range of 1.0 to 30% by weight. These copolymers belong to a type of polyolefin called linear low-density polyethylene (LLDPE), which is polymerized using a catalyst mainly containing transition metals. The copolymers used in the present invention are those mentioned above, and commercially available products include, for example, Urtozex, Neozex (both products of Mitsui Petrochemicals), and Dowrex (products of Dow Chemical). Ethylene-vinyl acetate copolymer (EVA) mixed with the above propylene-ethylene copolymer () or ethylene-α-olefin copolymer ()
As such, those having a crystalline melting point of 85 to 103°C are used. Furthermore, when performing a gassho-type seal, the layer that becomes the sealing surface, or when performing an envelope-type seal, both outer layers have a melt index of 0.2 to 4.0 (g/10 minutes), as shown in the figure, Within the vinyl acetate content range of 3 to 12%, U, V, W, X,
It is preferable to use a polygon within the range of Y and Z points. The figure is a relationship diagram between vinyl acetate content and melt index, with the vinyl acetate content (wt%) in EVA taken on the horizontal axis and the melt index (g/10 min) on the vertical axis. In the figure, point U where the vinyl acetate content is 3% and the melt index is 0.2 is represented by (3, 0.2). Therefore, this polygon is U (3, 0.2), V (12,
0.2), W (12, 0.5), X (9, 0.5), Y (5, 4.0)
,
It is a connection of Z (3, 4.0). The polymer melt index is ASTM D-
1238, etc., and the crystal melting point is the temperature at which the maximum value of the melting curve obtained is measured using a differential scanning calorimeter (PerkinElmer Model IB). In the present invention, PVDC is a copolymer consisting of 65 to 95% by weight of vinylidene chloride and 5 to 35% by weight of at least one unsaturated monomer copolymerizable with this. Examples of copolymerizable unsaturated monomers include vinyl chloride, acrylonitrile, and acrylic acid alkyl esters (alkyl groups with 1 carbon atoms).
~18 pieces) etc. Of these, vinylidene chloride-vinyl chloride copolymers are common. Known plasticizers, stabilizers, etc. can be added to this vinylidene chloride resin as necessary. Since α-olefin polymer and PVDC are inherently not compatible, a laminate thereof is likely to peel off. Particularly in the case of the present application, since long-term immersion in hot water is often required for sterilization, weak adhesion may cause peeling, resulting in poor appearance and reduced heat-resistant sealability. 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. As the adhesive layer, carboxylic acid-modified polyolefin, ethylene-vinyl acetate copolymer, ethylene-ethyl acrylate copolymer, styrene-butadiene block copolymer, etc. are used, and mixtures thereof are also preferred. The thickness of the adhesive layer is usually 1 to 3 microns. In the present invention, the outer layer (A) is a mixture of a propylene-ethylene copolymer () and EVA (), which have particularly good oil resistance, and the outer layer (B) is a propylene-ethylene copolymer () or an ethylene-α olefin. Mixtures of copolymers () and EVA () are used.
Ethylene-α olefin () and EVA in the outer layer (B)
When a mixture of () is used, the outer layer (B) is preferably used on the side not in contact with the contents.
Each outer layer is mixed with EVA (), which has excellent stretchability, so it is easy to stretch, and at 90℃
A film with a heat shrinkage rate of 15% or more can be easily obtained. If the proportion of EVA () exceeds 80% by weight, oil resistance and heat-resistant sealing properties will deteriorate, and when mixed with propylene-ethylene copolymer (), if EVA () is less than 55%, ethylene-α
When mixed with the olefin copolymer (2), if EVA (2) is less than 30% by weight, stretching will be insufficient and a film with excellent heat shrinkability cannot be obtained. Note that the ratio of EVA( ) may be the same or different in both outer layers. The ratio of EVA () to the total amount of polymers in both outer layers must be 40% by weight or more in order to obtain a film with good heat shrinkability. In the multilayer film according to the present invention, the thickness of each of the outer layers is preferably 18% or more of the total thickness of the laminated film. The thicknesses of both outer layers may be the same or different. This is because if the thickness of the layer that should be the sealing layer (at least one of the two outer layers for gassho seals, both outer layers for envelope seals) is less than 18%, problems may occur in heat-resistant sealing properties. The thickness of the core layer is required to be at least 2 μm or more to impart gas barrier properties, and is preferably 30% or less of the total thickness of the laminated film. If it exceeds 30%, there is a risk that the fall strength will be weakened. The thickness of the entire layer is generally in the range of 20 to 120 microns. The laminated film of the present invention can be produced by a generally known method. That is, using an extruder according to the number of laminated layers, cylindrical ones are extruded using a circular die similar to JP-A-53-82888, and flat ones are extruded using a known T-die. It is used to extrude into a flat shape and laminate. The cylindrical laminate is once rapidly cooled directly under the die, then folded with nip rollers, 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 sequentially or simultaneously biaxially stretched to obtain a heat-shrinkable laminate film. The heat-shrinkable laminated film obtained by the present invention has excellent oil resistance, heat-resistant sealing properties, and gas barrier properties, and is therefore used for packaging various foods. It has been particularly suitably used for packaging fatty foods that require high-temperature sterilization, 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. EXAMPLES A resin consisting of the polymers listed in Table 1 is extruded separately in a plurality of extruders and the molten material flows into a coextrusion annular die where it is formed into the desired laminate.
The cylindrical body of the laminate flowing out from the die has a temperature of 15 to 25°C.
It is cooled in a cooling tank with a flat width of 120 mm and a thickness of 270 mm.
Make it into a cylindrical shape of 540μ. Inside the cylindrical body in the cooling tank,
Filled with soybean oil to prevent inner surfaces from sticking together. Next, the cylindrical body was heated for about 12 seconds while being fed at a speed of 5 m/min through a hot water layer adjusted to have the stretching temperature shown in Table 2, and then heated for about 12 seconds at a rotation speed of 5 m/min. Pass through 1 nip roller. The cylindrical body is cooled in a normal temperature atmosphere and is
By the time it passes through the second nip roller, which rotates at 50 min, it is stretched 3 times in the longitudinal direction, and is expanded by air sent into the cylindrical body to 3 times the diameter of the cylindrical body, and stretched in the lateral direction. The resulting biaxially stretched film had a fold diameter of about 360 mm and a thickness of about 30 to 60 μm. Table 1 shows the physical properties of the polymers used in the examples.
The table shows the layer structure of the laminated film obtained in the example and the physical property test results of the obtained film, and Table 3 shows the method of testing the physical properties of the film.

[Table] *3 Product name Urtozex (manufactured by Mitsui Petrochemicals)

[Table] 〓Note〓 Stretchability ○: Stretchable, ×: Stretchable, but the film thickness is uneven due to slight netting, XX: Stretchable.
Oil resistance ◎ No deterioration observed (meatloaf, grilled pork) ○ No deterioration observed (meatloaf) × Tearing and swelling of the outer layer observed Heat-resistant sealability ◎ OK for 60 seconds or more (approximately equivalent to 10 minutes at 90℃ for grilled pork packaging) × Less than 10 seconds

[Table] As is clear from Examples 1 to 7 in Table 2, the multilayer films of the present invention all have excellent stretching methods, sufficient heat shrinkability at 90°C, and excellent oil resistance, heat sealing properties, and gas barrier properties. can be obtained. Incidentally, in the examples and comparative examples, except for the envelope seal of Example 6, all the others were heat-sealed in a folded palm type. In Comparative Example 1, the proportion of propyne-ethylene copolymer () in the outer layer (A) was 10% by weight, so oil resistance and
The heat-resistant sealability was poor, and in Comparative Example 2, since the proportion of the ethylene-α-olefin copolymer () in the outer layer (B) was 80% by weight, slight necking occurred and the stretchability was poor. Comparative Example 3 has poor heat-resistant sealing properties because it does not have an adhesive layer. Comparative Example 4 could not be stretched because the proportion of propylene-ethylene copolymer in both outer layers was 50% by weight.

[Brief explanation of drawings]

The accompanying drawing is a diagram showing the relationship between the melt index (vertical axis) and vinyl acetate content (horizontal axis) of the ethylene-vinyl acetate copolymer preferably used in the present invention.

Claims (1)

[Claims] 1. The core layer is made of vinylidene chloride copolymer, and the outer layer is made of vinylidene chloride copolymer.
(A) is a propylene-ethylene copolymer () having a crystal melting point of 130 to 155°C (20 to 45% by weight) and a crystal melting point of 85
It is a mixture of 80-55% by weight of ethylene-vinyl acetate copolymer () having a temperature of ~103°C, and the outer layer (B) is a mixture of 80-55% by weight of the ethylene-vinyl acetate copolymer () and the propylene-ethylene copolymer. A mixture of 20 to 45% by weight of the ethylene-vinyl acetate copolymer () and 80 to 30% by weight of the ethylene-vinyl acetate copolymer () and an ethylene-α-olefin copolymer () having a crystal melting point of 110 to 125°C
and the ratio of the ethylene-vinyl acetate copolymer () to the total amount of polymer in both outer layers is 40% by weight or more, and an adhesive layer is provided between the core layer and each outer layer. A heat-shrinkable laminated film with excellent oil resistance, heat-resistant sealing properties, and gas barrier properties. 2 Ethylene-α-olefin copolymer () is a copolymer of ethylene and one or more α-olefin selected from butene-1, pentene-1, 4-methylpentene-1, hexene-1, and octene-1. The laminated film according to claim 1, wherein the polymer is linear low-density polyethylene. 3 At least one layer of ethylene-vinyl acetate copolymer () is U (3, 0.2), V(12, 0.2), W
(12, 0.5), X (9, 0.5), Y (5, 4.0), Z (3
,
4.0) The first claim is characterized in that the polygon is selected from within the range of polygons formed by connecting
The laminated film according to item 1 or 2.