JPS625061B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for manufacturing a package that has good gas barrier properties and can be heat sterilized. More specifically, it is made of a multilayer plastic film consisting of a polyamide resin layer as the outermost layer, a modified polyolefin adhesive resin layer, a saponified ethylene-vinyl acetate copolymer resin layer, and a heat sealing resin layer, which has gas barrier properties, heat resistance, A method for producing a package in which food contents are degassed and packaged using a heat-shrinkable multilayer film with good transparency, and then heat sterilized in an atmosphere of 80°C to 100°C for more than 5 minutes. It is. In recent years, regulations on food additives have become stricter in the food processing industry, especially in the livestock meat processing and fish processing fields, and the amount of disinfectants used has been reduced or almost no longer used. In order to ensure freshness, packaging that has good oxygen gas barrier properties and can be heat sterilized is required.On the other hand, from the sales promotion aspect of market development,
There is a demand for a package with excellent transparency and a good appearance without folds and wrinkles, and the present invention is a package that satisfies these demands. Conventionally, laminated heat-shrinkable films of ethylene-vinyl acetate copolymer resin and vinylidene chloride resin, polypropylene resin, polyamide resin,
Laminated films made of polyethylene resin, etc. were used. However, although packaging using vinylidene chloride-based laminated heat-shrinkable film has excellent oxygen gas barrier properties, after deaerating the food contents and sterilizing them by heating in hot water at 80°C for 5 minutes, However, there are disadvantages in that pinholes sometimes occur in the package and delamination between films occurs. Packaging bodies using a laminated film of polypropylene resin and polyethylene resin or a laminated film of polyamide resin and polyethylene resin are:
It is possible to withstand heat sterilization in boiling water at 80°C to 100°C for 60 minutes after deaerating the food contents, but the oxygen gas barrier properties are poor and the contents, such as processed meat products or processed fish meat, can withstand heat sterilization for 60 minutes. The edible shelf life of the product is short, and at the same time, since the laminated film is not heat-shrinkable, the packaging after heat sterilization has the disadvantage that folds and wrinkles occur on the exterior, making it unsightly. As such, it has good oxygen gas barrier properties.
It meets all the required performance requirements, such as being able to heat sterilize for more than 5 minutes in an atmosphere of 80℃ to 100℃, and adding heat shrinkability to the plastic film in order to obtain a package with a good appearance and no folds or wrinkles. I have not been able to find a package that satisfies the requirements. The present inventor has discovered that an ethylene-vinyl acetate copolymer saponified resin with excellent oxygen gas barrier properties has stable and high gas barrier properties over a long period of time,
In addition, we conducted research to create a package that exhibits high heat shrinkability in boiling water and can be heat sterilized for a long period of time.The outermost layer is a polyamide resin layer, a modified polyolefin adhesive resin layer, and an ethylene-vinyl acetate layer. A multilayer plastic sheet consisting of a copolymer saponified resin layer and a heat seal resin layer is heated at 100℃.
These heat-shrinkable multilayer plastic films can be biaxially stretched at the following temperatures, and after degassing and packaging food contents,
It was discovered that heat sterilization for more than 5 minutes was possible in an atmosphere at .degree. C., and after further various studies, the present invention was completed. The purpose of the present invention is to ensure that the food contents can withstand heat sterilization for more than 5 minutes in an atmosphere of 80°C to 100°C after being degassed and packaged, and that they maintain oxygen gas barrier and moisture-proof properties for a long period of time. To provide a package using a heat-shrinkable multilayer plastic film for food packaging which is stable and has excellent low-temperature heat-shrinkability, transparency, hygiene, etc. The present invention comprises a polyamide resin layer (A) as the outermost layer, a modified polyolefin adhesive resin layer (B), an ethylene-vinyl acetate copolymer saponified resin layer (C), a heat seal resin layer (D), etc. A multilayer plastic film with a laminated structure including, for example, a multilayer plastic film starting from the outermost layer (A) - (B) - (C) - (B) - (D) or (A) - (C) - (B) - (D) or (A)-(C)-(A)-(B)-(D)
Or, it is a multilayer plastic film with a laminated structure in which (A)-(C)-(B) are adjacent to each other, and the total thickness of the film is
The size is 10μm to 200μm, and the dimensional shrinkage rate is 10% in both length and width after 10 seconds when placed in an atmosphere at a temperature of 100℃.
This package is characterized in that the contents are degassed and packaged using a heat-shrinkable multilayer film that has a temperature exceeding 80°C and is heat sterilized for more than 5 minutes in an atmosphere that exceeds 80°C. Polyamide resin is manufactured by polycondensation reaction of W-aminocarboxylic acid or dibasic acid and diamine, and is produced by polycondensation reaction of 6-nylon, 6-6 nylon,
Examples include 610-nylon, 11-nylon, 12-nylon, and copolymers thereof, and particularly preferred is a copolymer polyamide resin of ε-caprolactam and hexamethylene diammonium adipate. Modified polyolefin adhesive resins are modified polypropylene resins obtained by graft copolymerization of polar groups such as unsaturated carboxylic acids, modified polyethylene resins, modified ethylene-vinyl acetate copolymer resins, or blends or comonomers thereof. These include ionomer resins, among which modified ethylene-vinyl acetate copolymer adhesive resins have good adhesive performance, and modified polypropylene adhesive resins have good heat resistance and are therefore preferred. The saponified ethylene-vinyl acetate copolymer resin has a softening temperature (flow tester method) of 150°C to 175°C, an ethylene content of 25 to 75 mol%,
Saponification degree of vinyl acetate in copolymer is 90%
As described above, it has extremely high oxygen gas barrier properties in a dry state. Heat-sealing resin is a polyolefin resin, including low-density polyethylene resin, medium-density polyethylene resin, high-density polyethylene resin, and ethylene-based resin.
Vinyl acetate copolymer resin, polypropylene resin,
It is one type of ionomer resin and a copolymer of each resin, or a blend thereof. The total thickness of the plastic film used in the present invention is from 10 μm to 100 μm, and plastic films with a thickness within this range are suitable for shrink-wrapping foods. The purpose of the present invention is to shrink wrap and heat sterilize packages for foods, so items to be packaged, such as processed food products, are filled into bags made of a heat-shrinkable multilayer film, and after the inside is deaerated, the opening Heat seal and heat to 80℃~
Heat sterilization is performed at the same time as shrink wrapping by placing the product in boiling water at 100°C or in a heating chamber for more than 5 minutes. When the food contents are packaged in a heat-shrinkable multilayer film and the inside is degassed, the food contents are heated, the multilayer film shrinks, the food contents and the multilayer film come into close contact, and the multilayer film is folded and wrinkled. It is possible to obtain a package with a good appearance, and at the same time, it is possible to heat sterilize the package with this appearance. The heat-shrinkable multilayer film for this purpose is at least
It must have a dimensional shrinkage of more than 10% in the vertical and horizontal directions after 10 seconds of being placed in an atmosphere at a temperature of 100℃, and must be able to withstand heat sterilization in an atmosphere of 80℃ to 100℃ for more than 5 minutes. Peeling of the heat-sealed portion does not occur. The method of deaerating food contents is carried out by a single method or multiple methods, in which the food contents are filled into a bag-shaped bag made of a heat-shrinkable multilayer film,
After the inside of the bag is degassed with a degassing pressure of 760 mmHg, the opening is heat-sealed. The method for producing a heat-shrinkable multilayer film used in the present invention includes a polyamide resin layer as the outermost layer, a modified polyolefin adhesive resin layer, an ethylene-vinyl acetate copolymer saponified resin layer, a heat seal resin layer, etc. A multilayer plastic sheet having a laminated structure, the multilayer plastic sheet is melt extruded from a laminated die by a coextrusion method using a plurality of extruders, cooled and solidified, and then
Reheating to a stretching temperature within the range of ℃ to 100℃,
It is characterized by being biaxially stretched by 1.5 times or more in the longitudinal direction and 1.5 times or more in the transverse direction, and then cooled. The laminated structure of the multilayer plastic sheet before stretching must have a polyamide resin layer as the outermost layer for packaging the food contents, and the coextrusion method for the multilayer sheet includes extruding it into a tube shape using a circular die. Alternatively, it is preferable to extrude it into a flat shape using a T-die. Next, this tube-shaped sheet or flat-shaped sheet is reheated to a stretching temperature within the range of 70°C to 100°C, and subjected to simultaneous biaxial stretching in the longitudinal and lateral directions or sequential biaxial stretching by a known tubular or tenter stretching method. By doing so, a film with good appearance can be produced. After deaerating processed food products using the heat-shrinkable multilayer film of the present invention produced by the above-mentioned production method, the package after heat sterilization was immersed in boiling water at 100°C for 60 minutes. The processed food product could be stored for a long period of time without any abnormalities such as folding and wrinkles that worsened the appearance or damage to the package. The main effect of the packaging body of the present invention is that polyamide resin and saponified ethylene-vinyl acetate copolymer resin, which are extremely difficult to be biaxially stretched at temperatures below 100°C, are heat-sealed to the resin through an adhesive resin. This multilayer structure enables biaxial stretching of the polyamide resin layer and the saponified ethylene-vinyl acetate copolymer resin layer at a temperature of 100°C or less, and also allows the polyamide resin layer to be stretched to the maximum. Because the outer layer is used as a package using these heat-shrinkable multilayer films, after the contents are deaerated and packaged,
It was discovered that heat sterilization for more than 5 minutes in an atmosphere of 80°C to 100°C is possible. The stretching ratio of the biaxial stretching is 1.5 times or more in both length and width, preferably 2 times to 4 times. 100℃
In order for the dimensional shrinkage rate to exceed 10% in both the vertical and horizontal directions after 10 seconds of being placed in an atmosphere of The dimensional shrinkage rate (α) is the length of the original film.
l ₀ , put it in an atmosphere at a constant temperature, and let the length of the film after a certain time be l, then α=100・(l ₀ −
l)/l ₀ (%). The heat-shrinkable multilayer film of the present invention can be heated from 70°C to 90°C.
The dimensional shrinkage rate after 10 seconds after being placed in an atmosphere at ℃ is 20
% to 50%. In order to obtain such a film, it is preferable to carry out biaxial stretching of 2 to 4 times both length and width at a temperature of 70°C to 90°C. Next, examples of the present invention will be described. Table 1 shows examples of the present invention.

[Table] The original film sheets of Examples No. 1 to No. 7 shown in Table 1 were all produced by the T-die coextrusion method, melt-extruded from a multilayer die, and
A sheet with a thickness of μm was produced. Next, the sheet was reheated using a biaxial stretching device, and then stretched twice in both length and width to form a film with a thickness of approximately 50 μm, which was then subjected to stretchability, heat shrinkability, oxygen gas barrier properties, and package heating tests. We evaluated gender, etc. Regarding the film appearance, those with good transparency and smoothness and no stretching unevenness were evaluated as good, and those with stretching unevenness due to netting or with poor smoothness and transparency were evaluated as poor. The thickness of each layer of the film is shown in correspondence with the order of construction and the order of thickness construction from left to right. For heat shrinkage, put the film in boiling water,
After a second, take it out and cool it, and before and after boiling, both vertically and horizontally.
Those showing a dimensional shrinkage rate of over 10% are considered good.
Anything less than that was considered defective. Oxygen gas barrier properties are determined using test method ASTM-D.
-1434, measured in a dry state at 20°C. Oxygen gas barrier properties are good below ^30c.c./M2・24hr・ATM. The package heating testability was determined by vertically testing the various films mentioned above.
Processed into a three-sided sealed bag measuring 13 cm by 13 cm in width, the bag is filled with grilled pork, which is an irregularly shaped processed food product with protrusions weighing approximately 200 g, as the food content,
After deaerating the inside of the bag with a degassing pressure of 760 mmHg, heat seal the mouth part in a deaerated state. As a sealing method, a hot plate sealer heated to 130° C. is used, and sealing is performed with a hot plate pressure of 2 kg/cm ² and a heating time of 1 second. The package thus obtained is heated to 80°C or 100°C.
Shrink wrap and heat at the same time in hot water at ℃ for 5 or 60 minutes, and the test quantity is 10 pieces at the same test level. After heating, a product with no degassing leak due to a broken seal or pinhole is considered good, and a product with even 1 out of 10 degassing leaks is considered bad. In the overall evaluation of the packaging, the appearance of the film,
Those that are good in all of the heat shrinkability, oxygen gas barrier properties, and packaging heat test properties are rated as good (○), and those that are defective in any of them are rated as poor (x). In Table 1, polyamide resin has a melting point of 190
The saponified ethylene-vinyl acetate copolymer resin is Eval manufactured by Kuraray Co., Ltd., which has a softening temperature (flow tester method) of 170°C. Polymer adhesive resin, modified polypropylene adhesive resin, and modified polyethylene adhesive resin are manufactured by Mitsubishi Yuka Co., Ltd.
The ethylene-vinyl acetate copolymer resin is Evatate (vinyl acetate content 8% by weight) manufactured by Sumitomo Chemical Co., Ltd., and the low density polyethylene resin is manufactured by Sumitomo Chemical Co., Ltd. with a melting point of 105°C. The polypropylene resin is an ethylene-propylene random copolymer polypropylene resin manufactured by Sumitomo Chemical Co., Ltd. with a softening temperature of 140°C, and the ionomer resin is an ethylene-methacrylic acid copolymer with a melting point of 99°C and Zn. It is a resin treated with ions and is Himilan manufactured by Mitsui Polychemical Co., Ltd. As is clear from Examples No. 1 to No. 6, the packaging of the present invention has transparency, an appearance of the packaging with no creases due to low-temperature heat shrinkability, and extremely good oxygen gas barrier properties. The package can be heated for 5 to 60 minutes in an atmosphere of 80°C to 100°C. As is clear from Examples No. 7 and No. 8, it was found that the package containing the saponified ethylene-vinyl acetate copolymer resin layer as the outermost layer did not withstand the package heat test, and was It has been found that packages containing an unstretched polypropylene resin layer as an outer layer can withstand the package heat test, but have no heat shrinkage and have poor oxygen gas barrier properties. This does not result in a package that satisfies all of the requirements such as low-temperature heat shrinkability, oxygen gas barrier properties, and package heating testability in an atmosphere of 80°C to 100°C for more than 5 minutes.

Claims (1)

[Claims] 1. Two layers consisting of a polyamide resin layer (A), a modified polyolefin adhesive resin layer (B), an ethylene-vinyl acetate copolymer saponified resin layer (C), and a heat seal resin layer (D). The total thickness of the axially stretched multilayer plastic film, the outermost layer of which is a polyamide resin layer (A) and the innermost layer of which is a heat sealing resin layer (D), is
10 to 200 μm, placed in an atmosphere at a temperature of 100°C, degassed the contents in a heat-shrinkable film with a dimensional shrinkage rate of over 10% in both length and width, and wrapped in an atmosphere at a temperature of over 80°C for 5 minutes. A method for manufacturing a package, which comprises heating and sterilizing the package. 2 Biaxially stretched multilayer plastic film is formed from the outermost layer (A)-(B)-(C)-(B)-(D), (A)-(C)-(B)-(D) or (A ) - (C) - (A) - (B) - (D) The method for producing a package according to claim 1, wherein the package is laminated in the order of (A) - (B) - (D).