JPH0455109B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention relates to a heat-shrinkable composite stretched film that can be suitably used for vacuum packaging raw meat. (Prior art) As a film for vacuum packaging chilled raw meat, a heat-shrinkable film using polyvinylidene chloride resin or a polyamide resin such as nylon 6 is used as an intermediate layer, and the inner and outer layers are laminated with various resins. A stretched composite stretched film is used. (Problems to be Solved by the Invention) The film with the above-mentioned polyamide resin as an intermediate layer has excellent strength, but when raw meat is vacuum packaged, the film itself becomes finely wrinkled and its adhesion to the surface of the raw meat deteriorates. As a result, drips from the raw meat were observed to migrate to the wrinkled areas, causing problems in the appearance and storage of the package. As a means to improve the adhesion, attempts were made to increase the stretching ratio during film production and increase the shrinkage rate of the film at low temperatures, but the shrinkage rate did not increase significantly and the adhesion was significantly improved. No effect was observed. (Means for Solving the Problems) The present invention improves the adhesion to raw meat by using a copolyamide resin having a specific composition, and the gist thereof is is a composite stretched film in which the outer layer and the inner layer are polyolefin layers, and an intermediate layer consisting of a polyamide resin or a polyamide resin layer and a saponified ethylene-vinyl acetate copolymer layer is provided between the two layers, the polyamide resin layer being The heat-shrinkable composite stretched film is characterized in that it consists of a copolyamide resin mainly composed of nylon 6 and other components being a polycondensate of hexamethylene diamine and terephthalic acid and/or isophthalic acid. The copolyamide resin used in the intermediate layer of the composite film of the present invention is mainly composed of nylon 6, with the other components being a polycondensate of hexamethylene diamine and terephthalic acid (hereinafter referred to as "6-6T nylon").
That's what it means. ) or similarly, a product mainly composed of 6-6I nylon, with the other components being a polycondensate of hexamethylene diamine and isophthalic acid (hereinafter referred to as "6-6I nylon")
That's what it means. ). Further, a combination of both of the above acids may be used. The composition ratio of the above copolymerized polyamide resin is 95 to 80% by weight of nylon 6, and the proportion of other components.
It is preferable that the amount of 6T nylon or 6I nylon or a mixture thereof is in the range of 5 to 20% by weight, and if the other components are less than 5% by weight, no effect of improving adhesion can be seen, and if the other components are 20% by weight It is difficult to produce a copolymer if it exceeds this range, which is disadvantageous. The thickness of this copolyamide resin layer is 10~
It is necessary to keep the film thickness in the range of 16 μm; if it is less than 10 μm, the stretchability during film formation will be poor, and if it exceeds 16 μm, the flexibility of the film will be lost, which is disadvantageous. In addition, the intermediate layer may be a combination of the polyamide layer and an ethylene-vinyl acetate saponified material layer in order to improve gas barrier properties.
It can be suitably used if the saponification degree is 95 mol % or more and the layer thickness is 3 to 7 μm. As the polyolefin used for the outer layer and the inner layer, ionomer resins, polyethylene, copolymers of ethylene and other components, such as ethylene-vinyl acetate copolymers, ethylene-propylene copolymers, etc. can be used. The thickness of the inner layer must be 25μ or more; if it is less than 25μ, the film will not be easily penetrated by the small bones and cartilage remaining on the surface of raw meat (hereinafter referred to as "breakthrough resistance"). There is a drawback. The film of the present invention is generally produced by laminating layers by coextrusion and then stretching by inflation. The stretching ratio is preferably within the range of 2.0 to 4.0 times in both the longitudinal direction (the direction in which the film is taken) and the transverse direction (direction perpendicular to the above direction). If the stretching ratio is less than 2.0 times, the shrinkage rate will decrease. If it exceeds 4.0 times, the film tends to break during film formation, which is inappropriate. The stretching temperature can be in the range of 120 to 140°C. For vacuum packaging of raw meat, it is preferable to select stretching conditions within this range so that the shrinkage rate at 75° C. is 20% or more in both the longitudinal and transverse directions. Hereinafter, the present invention will be explained with reference to Examples. (Example) Example The outer layer and inner layer are made of ethylene-vinyl acetate copolymer with a vinyl acetate content of 5 mol%, and the middle layer is an ethylene-vinyl acetate copolymer with an ethylene content of 45 mol% and a saponification degree of 99 mol%. Saponified layer or/and table-
A polyamide resin layer with the contents shown in Table 1 was used, and the thickness was as shown in Table 1.
After laminating at 240℃), the stretching ratio was set as shown in Table 1 by the inflation method, and the stretching temperature was
It was stretched at 130°C to obtain a tube with a folded diameter of 50cm. Bottom-seal the resulting tube and fold it to a diameter of 45.
A bag was prepared with a size of 60 cm x 60 cm, and after filling the bag with about 7 kg of chilled beef, the opening was impulse-sealed and vacuum packaging was performed using a vacuum packaging machine manufactured by Multibag. Next, each package was heat-shrinked using a hot water shower at 80 to 85°C. Table 1 shows the "shrinkage rate", "adhesion" and "breakthrough resistance" of each of the above films. "Shrinkage rate" is determined by measuring the length L' of the film after shrinkage by immersing the film in a hot water bath controlled at 75°C or 85°C for 1 minute, with L being the length of the film before shrinkage. Value calculated by (L-L'/L) x 100. "Adhesion" was determined by observing whether or not dripping occurred after each of the above packages was stored at 3° C. for 4 weeks. A sample with good appearance and almost no dripping between the film and the raw meat was graded as (○), and a sample with a slight tendency to drip was graded as (△). "Break resistance" was determined by filling each film with raw meat, particularly from areas with many small bones, and then vacuum-packaging the film, and observing whether or not the film had broken through. Items with no tearing or scratches were rated as (○), and items that were difficult to use because they were easily broken were rated as (x).

[Table] From Table 1, it can be seen that the invented products (1) to (4) have a large shrinkage rate even at a low stretching ratio, good adhesion, and excellent puncture resistance. On the other hand, for comparison products (1) to (2), which have the same structure as the invented products (1) to (3) but differ only in nylon, the shrinkage rate is difficult to increase even if the stretching ratio is increased, and the adhesion is inferior. I understand that. Furthermore, it can be seen that Comparative Product (3) has good adhesion, but is inferior in break-through resistance. (Effects of the Invention) As explained above, the heat-shrinkable composite stretched film of the present invention has excellent adhesion and puncture resistance, and therefore can be suitably used for vacuum packaging of raw meat.

Claims (1)

[Claims] 1. A composite stretched film in which the outer layer and the inner layer are polyolefin layers, and an intermediate layer consisting of a polyamide resin layer or a polyamide resin layer and a saponified ethylene-vinyl acetate copolymer layer is provided between both layers,
The polyamide resin layer is mainly made of nylon 6,
A heat-shrinkable composite stretched film comprising a copolyamide resin containing a polycondensate of hexamethylene diamine and terephthalic acid and/or isophthalic acid as another component.