JPS642512B2 - - 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 for deep-drawn bottom material suitable for packaging foods such as sliced ham. Conventionally, various dry laminated films,
Coextruded composite films are on the market. However, since dry laminated film uses adhesive, the film does not stretch well during pressure (or vacuum) forming, resulting in insufficient forming, and when filled with sliced ham, etc., many wrinkles occur at the bottom. The disadvantage is that it spoils the appearance. Further, although the conventional coextruded composite film has good film elongation, it has the disadvantage that the adhesive strength between each base film is weak and delamination between the films occurs during molding. The present inventors have previously proposed a combination of base films that does not cause delamination between films.
The patent application was filed for a four-layer coextruded composite film that does not cause delamination during molding, but even with this composite film, the contents may deform or wrinkles at the bottom due to dimensional changes in the film over time. It still has some shortcomings and is not completely satisfactory. As a result of various studies, the present inventors have completed a four-layer co-pressed composite film that improves the conventional drawbacks.The gist is that the first layer has an ethylene content of 30 to 60 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, the third layer is a modified polyolefin, and the fourth layer is a sealing material layer selected from ionomer resin, polyethylene, or a copolymer of ethylene and other components, and the thickness of the second layer is is 5~
It is a four-layer coextruded composite film in the 15μ range. The reason why the ethylene-vinyl acetate copolymer (hereinafter referred to as "EVAOH") layer is used as the first layer (outer layer) is to suppress the dimensional change due to moisture absorption of the second layer, the nylon layer, and to add gloss to the film surface. This is for the purpose of granting. The EVAOH to be used should have an ethylene content of 30 to 60 mol%, and its degree of saponification should be 95 mol% or more, and the thickness should be 10 μ or more, and more preferably 10 to 30 μ, in terms of preservation of the contents and cost. preferable. If the ethylene content is less than 30 mol%, the crystallinity will be high and the moldability during coextrusion molding or pressure (or vacuum) molding will be poor, and if it exceeds 60 mol%, the oxygen barrier properties will be poor. Not suitable for preserving food. If the degree of saponification is less than 95 mol%, heat treatment such as molding may cause cloudiness due to extremely small amounts of moisture penetrating from the outside, and peeling between film layers may occur. The reason why a 6-66 nylon resin containing 5% by weight or more of the 66 component is used in the second layer is to provide the strength of the composite film itself to the nylon layer. 66
If a component with a content of less than 5% by weight is used, it will crystallize during coextrusion molding, resulting in a relatively hard composite film, will have poor elongation during air pressure (or vacuum) molding, and will be difficult to maintain after filling with the contents. The drawback is that there are wrinkles at the bottom. The thickness of the 6-66 nylon layer is best in the range of 5 to 15 microns. In other words, if the thickness of the 6-66 nylon layer is less than 5 μm, a film with good appearance cannot be obtained.
Moreover, the strength (pinhole resistance) of the composite film becomes insufficient. If the thickness exceeds 15μ, tensile stress increases, resulting in poor elongation and poor formability.
Furthermore, the shrinkage stress increases when the dimensions change due to moisture absorption, resulting in deformation of the contents and wrinkles at the bottom over time. The modified polyolefin used in the third layer is a polyolefin resin grafted with at least one monomer selected from unsaturated carboxylic acids or derivatives thereof. By firmly adhering the two 6-66 nylon layers, the nylon layer and the sealing material layer, which have conventionally caused delamination, are firmly adhered. The thickness of the third layer is 10μ
A good value is between ~30μ. The fourth sealing material layer uses a sealing material selected from ionomer resin, polyethylene, or a copolymer of ethylene and other components to improve the sealing performance with the lid material and completely protect the contents. It is to make it. The thickness of the fourth layer is 50~
A value between 130μ is good. The total thickness range from the first layer to the fourth layer is typically between 120μ and 160μ. In the present invention, since the resin layers having the above structure are laminated by coextrusion, the resin layer has good elongation during pressure (or vacuum) molding, and has excellent workability.Wrinkles do not occur on the bottom immediately after molding, and the film remains stable over time. A coextruded laminated film with a good appearance for use as a deep-drawn bottom material that does not cause content deformation or bottom wrinkles due to dimensional changes can be obtained. This will be explained in detail in Examples below. [Example] Various composite films obtained by the method described below were heated at 100°C for 2 seconds with a deep drawing machine MVP-401 manufactured by Mitsubishi Heavy Industries, Ltd. so that the first layer was on the outside.
It was drawn to a size of 100 mm in diameter and 30 mm in depth at a gauge pressure of 3.0 Kg/cm ² . Immediately fill the formed hole with 200g of sliced ham with a diameter of 98mm,
After covering with the following lid material and vacuum packaging, 160mm x 130
Each package was cut into a rectangle of mm. Immediately after vacuum packaging, each package obtained was left for one week (5℃, 100℃
Table 1 shows the appearance (wrinkles on the bottom, etc.), pinhole resistance (Note 1), and gas barrier properties (Note 2) after the test was carried out (in an atmosphere of % relative humidity). 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, so that it had a composition of ethylene-vinyl acetate copolymer with a vinyl acetate content of 5%.
Each resin was laminated 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 as follows:
The thickness of the second layer is 5μ, the third layer is 15μ, and the fourth layer is 90μ. Invention (2) Composite films with different thickness configurations were obtained by coextrusion using the same material as invention (1). The first layer has a thickness of 20μ, the second layer has a thickness of 15μ, the third layer has a thickness of 15μ, and the fourth layer has a thickness of 100μ. Invention (3) A laminated film using the same materials as the invention, except that an ionomer resin (Himilan, manufactured by Mitsui Polychemical Co., Ltd.) was used as the fourth sealing material layer. The thickness of each layer is 20μ for the first layer and 20μ for the second layer.
15μ, the third layer is 15μ, and the fourth layer is 100μ. Comparative product 1 Composite films with different thickness configurations were obtained by coextrusion using the same material as the invention product (1). The first layer has a thickness of 20μ, the second layer has a thickness of 30μ, the third layer has a thickness of 15μ, and the fourth layer has a thickness of 85μ. Comparative product 2 Invention product (1) with 6-66 nylon containing 15% by weight of 66 nylon as the first layer (outer layer) and as the second layer,
The EVAOH used in (2) and (3) was mixed with nylon 6 as the third layer and ionomer resin (Himilan, manufactured by Mitsui Polychemical Co., Ltd.) as the fourth sealing layer. The resin is laminated in a coextrusion annular die at a set temperature of 250°C, then cooled to reduce the diameter.
A 270mm inflation film was obtained. 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 3 A commercially available dry laminate film in which 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 ionomer resin (Himilan, manufactured by Mitsui Polychemical Co., Ltd.). The thickness of each layer is 40μ for the first layer and 40μ for the second layer.
50μ and the third layer is 60μ. Comparative product 4 The first layer (outer layer) was EVAOH used in invention products (1), (2), and (3), and the second layer was a modified polyolefin (ADMER LF-305, manufactured by Mitsui Petrochemical Industries, Ltd.). )of,
Vinyl acetate content is 5% as the third layer is a sealing material layer.
Coextrusion molding was carried out using an ethylene-vinyl acetate copolymer composition. The thickness of each layer is as follows:
30μ, the second layer is 15μ, and the third layer is 105μ. The lid material is made of unstretched polypropylene (thickness
A film consisting of vinylidene chloride-coated cellophane (30μ)/ionomer resin (30μ) was used. Note 1 Pinhole resistance Each package is placed in a type A single cardboard case.
105 pieces were stacked in 3 rows and 7 stacks, and the packaged items were dropped horizontally from a height of 60 cm 5 times and dropped once on 6 sides, and then the packaging was checked for pinholes using an energization method. Note 2 Gas barrier property After creating a molded product with a diameter of 100mmφ and depth of 25mm using each component film as the bottom material and aluminum (40μ)/polyethylene (100μ) as the lid material, nitrogen gas was added to the molded product. The encapsulated film (the molded product was in an atmosphere of 100% relative humidity) was left in an atmosphere of 5° C. and 75% relative humidity, and the oxygen permeability of each constituent film was checked.

[Table] (Note) ○...Good appearance △...Slightly bad ×...
Defective Table 1 shows that compared to Invention Products 1, 2, and 3, Comparative Product 1 has the same combination of base films as Invention Products 1 and 2 but has a thicker nylon layer, and Comparative Product 2 has a nylon layer on the outer layer. In this case, changes in appearance over time such as wrinkles on the bottom were observed, indicating that the container was unsuitable for use as a packaging container. Comparative product 3, which is a dry laminated product, has significant drawbacks such as large and numerous wrinkles at the bottom immediately after molding, and poor gas barrier properties. Comparative product 4, which is a three-layer product obtained by removing the nylon layer from the combination of the base films of invention products 1 and 2, has a good appearance with no wrinkles on the bottom like the invention product, but it has poor pinhole resistance and cannot be used as a food container. It turns out that it is not suitable as such. The present invention provides a coextruded composite film for deep drawing bottom material 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 60 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
The layer is a modified polyolefin, the fourth layer is a sealing material layer selected from ionomer resin, polyethylene, or a copolymer of ethylene and other components, and the thickness of the second layer is in the range of 5 to 15μ. Co-extruded composite film of layers.