JPS6321612B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a four-layer coextruded composite film,
More specifically, the present invention relates to a coextruded composite film suitable for packaging products such as sliced ham that require boiling sterilization. Conventionally, various dry laminated films and coextruded composite films have been marketed as this type of film for packaging foods such as sliced ham that require boiling sterilization. However, after forming the film under pressure (or vacuum) to match the external shape of sliced ham, etc., filling it with sliced ham and sealing it with a lid, boil sterilization in hot water (80℃). Because dry laminated film uses adhesive in the 30-minute soaking process,
Conventional coextruded composite films have the disadvantage that the film does not stretch well during air pressure (or vacuum) forming, resulting in insufficient forming, and when filled with sliced ham, etc., the bottom part becomes wrinkled, spoiling the appearance. Although the film has good elongation, the adhesion strength between each base film is weak, resulting in delamination between the films during molding and boil sterilization. As a result of various studies, the present inventors have completed a four-layer coextruded composite film that improves the conventional drawbacks, and the gist is that the first layer has an ethylene content of 30 to 58 mol%. A saponified ethylene-vinyl acetate copolymer with a saponification degree of 95 mol% or more, a second layer containing 66 components of 5% by weight or more
-66 nylon copolymer, third layer is modified polyolefin, fourth layer is ionomer resin or ethylene -
It is a four-layer coextruded composite film consisting of a sealing material layer selected from vinyl acetate copolymer, and the first to fourth layers are laminated in this order. The ethylene-vinyl acetate copolymer (hereinafter referred to as "EVAOH") layer is used as the first layer (outer layer) because EVAOH's excellent oxygen barrier properties preserve the contents for a long time and also allow them to be sterilized by boiling. This is to prevent the melters from sticking together due to hot water. The EVAOH used preferably has an ethylene content of 30 to 58 mol% and a saponification degree of 95 mol% or more. If the ethylene content is less than 30 mol%, the degree of crystallinity will increase and the molding processability during coextrusion molding or pressure (or vacuum) molding will deteriorate, resulting in a reduction of 58 mol%.
If it exceeds this, the oxygen barrier properties will deteriorate and it will be unsuitable for preserving food packaging. If the degree of saponification is less than 95 mol%, extremely small amounts of water that penetrated during boil sterilization may cause cloudiness or peeling between film layers. The reason why a 6-66 nylon layer containing 5% by weight or more of the 66 component is used as the second layer is to provide the strength of the composite film itself to the nylon layer, and the nylon layer has a water absorption rate other than that of the 6-66 nylon layer. It has a high water absorption rate compared to the resin layer, and when used as the outermost layer, it absorbs water, resulting in a decrease in oxygen barrier properties, dimensional changes, and peeling. When the content of 66 components is 5% by weight or more, it is difficult to crystallize during coextrusion molding, and a soft composite film can be obtained, and it has good elongation during air pressure (or vacuum) molding, and even after being filled with the contents. Although the appearance is good, if the content is less than 5% by weight, it will crystallize during coextrusion molding, resulting in a relatively hard composite film, and will also have poor elongation during air pressure (or vacuum) molding, causing the contents to be lost. There is a drawback that wrinkles appear at the bottom after filling. Modified polyolefins used in the third layer include, for example, Admer (manufactured by Mitsui Petrochemical Industries, Ltd.), Modelix (manufactured by Mitsubishi Yuka Co., Ltd.), etc., and by using these, the fourth layer can be The sealing material layer and the second 6-66 nylon layer are strongly bonded, and the nylon layer and the sealing material layer, which have conventionally caused delamination, are firmly bonded. The thickness of the third layer is preferably between 5μ and 30μ.
The fourth sealing material layer uses a sealing material selected from ionomer resin or ethylene-vinyl acetate copolymer to improve sealing performance with the lid material and ensure complete storage of contents. In the present invention, the resin layers having the above structure are laminated in this order from the first layer to the fourth layer by a coextrusion method, so that the elongation during pressure (or vacuum) molding is good and the processability is excellent. Since the 6-66 nylon layer, which has a lower melting point than 6-66 nylon, is used, the temperature of the co-extrusion die can be set lower than the extrusion temperature of 6-66 nylon, so the resulting laminated film is a co-extruded laminated film with less thermal deterioration as a whole. A film is obtained. This will be explained in detail in Examples below. [Example] Each composite film obtained by the method described below was
After heating at 100℃ for 2 seconds with a deep drawing machine MVP-401 manufactured by Mitsubishi Heavy Industries, Ltd. so that the layer is on the outside, it is heated to 3.0℃.
It was drawn to a size of 100 mm in diameter and 30 mm in depth at a gauge pressure of Kg/cm ² . Immediately, 200 g of sliced ham with a diameter of 98 mm was placed in the formed hole, and the lid material described below was placed on top, vacuum packaged, and then each package was cut into rectangles of 160 mm x 130 mm. The appearance (wrinkles on the bottom, etc.) after each package was sterilized by boiling in hot water at 80°C for 30 minutes, as well as the degree of haze (Note 1) and delamination strength (Note 2) before and after boil sterilization. )
are shown in Table-1. Invention (1) Ethylene content 45 mol% in the first layer (outer layer),
EVAOH with a saponification degree of 99.5 mol% as the second layer
6-66 nylon with a 66 nylon content of 15% by weight and modified polyolefin (Admer) as the third layer.
LF-305 (manufactured by Mitsui Petrochemical Industries, Ltd.) was used as the fourth sealing material layer, and ionomer resin Surlyn A (manufactured by Mitsui Polychemicals, Ltd.) was used.
The first to fourth layers were laminated in this order in a coextrusion annular die at a set temperature of 230° C., and then cooled to obtain a blown film with a diameter of 270 mm. The thickness of each layer is 20μ for the first layer and 20μ for the second layer.
30μ, the third layer is 20μ, and the fourth layer is 80μ. Invention (2) A laminated film having the same structure as Invention (1) except that an 80μ thick ethylene-vinyl acetate copolymer with a vinyl acetate content of 5% was used as the fourth sealing material layer. Comparative product 1 The first layer (outer layer) is 6-66 nylon with a 66 nylon content of 15% by weight, and the second layer is the invention product (1).
EVAOH used in (2) is used as the third layer and nylon 6 is used as the fourth sealing material layer to form the first layer in a circular die by coextruding each resin at a set temperature of 250℃. After laminating the first to fourth layers in this order, the mixture was cooled to obtain an inflation film having a diameter of 270 mm. The thickness of each layer is 20μ for the first layer, 20μ for the second layer,
The thickness of the third layer is 20μ, and the thickness of the fourth layer is 90μ. Comparative product 2 The first layer is unstretched polypropylene, the second layer is a 6-nylon layer coated with vinylidene chloride, and the third layer is a sealing material of Surlyn A, and the first to fourth layers are laminated in this order. The thickness of each layer is 40μ for the first layer and 40μ for the second layer.
50μ, and the third layer is 60μ. Lid material, unstretched polypropylene (thickness 20μ)/
Lid material made of cellophane (30μ)/Surlyn A (30μ) coated with vinylidene chloride. Note 1 Haze Measured according to JIS K6718 Note 2 Delamination strength Five samples each with a length of 100 mm and a width of 25 mm are taken from the longitudinal direction (the direction in which the film is taken) and the transverse direction (direction perpendicular to the longitudinal direction) of each laminate film. The interlayers with weak delamination strength of each constituent film (the second and third layers in Invention Products 1 and 2, the third and fourth layers in Comparative Product 1, and the high strength in Comparative Product 2) (Non-peelable) was peeled to a length of 50 mm from one end, each peeled end was caught in the chuck of a tensile tester, and the strength was measured by peeling at a speed of 200 mm/mm and the average value was recorded. did.

【table】

[Table] From Table 1, compared to Inventions 1 and 2, Comparative Product 1 had weaker delamination strength overall, and the adhesive strength decreased significantly before and after boiling, and delamination was immediately observed in some parts of the package. It can be seen that it is not suitable for packaging containers, as it can be easily used as a packaging container. Comparative product 2 has a strong delamination strength, but has many wrinkles and is found to be unsuitable as a food packaging container. The present invention provides a coextruded composite film suitable for food packaging, and its effects are significantly large.

Claims (1)

[Claims] 1 The first layer is a saponified ethylene-vinyl acetate copolymer with an ethylene content of 30 to 58 mol% and a saponification degree of 95 mol% or more, and the second layer is a saponified ethylene-vinyl acetate copolymer with a content of 66 components of 5% by weight or more. 6-66 nylon copolymer, 3rd
A four-layer coextruded composite in which the layer is a modified polyolefin, the fourth layer is a sealing material layer selected from an ionomer resin or an ethylene-vinyl acetate copolymer, and the first to fourth layers are laminated in this order. film.