JP2008074463A - Lid material for plastic container - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a lid material for a plastic container which prevents a lid from being torn when the lid is peeled to unseal a package for microwave cooking that is prepared by filling the plastic container with such a content article as rice, sealing the container with the lid by heat, and subjecting the container to retort treatment. <P>SOLUTION: The lid material for the plastic container is formed of a laminate including a heat sealing resin inner layer, a biaxially stretched polyamid resin intermediate layer formed by simultaneous biaxial stretching using a tubular method, and a gas barrier resin outer layer with a nonorganic material thin layer. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a lid member that is heat-sealed to a flange portion of a plastic container.

In recent years, food containers such as cooked rice are filled in a plastic container having a flange portion, sealed by heat-sealing a lid on the flange portion, retorted, and cooked in a microwave oven when eating. There are various known.
And as a cover material used for these microwave oven packaging bodies, in order from the inner layer side with respect to the container, an easily peelable thermally adhesive resin layer, a stretched nylon film, and a barrier film formed by forming a thin film layer of an inorganic substance. A lid member made of a laminated material in which is disposed is proposed. (For example, see Patent Document 1)
JP-A-6-286765

In addition, in order to prevent deformation and curling during heat sterilization due to boiling, retort, etc., there is also a cover film that uses a biaxially stretched polyamide film with a small hot water shrinkage as a base and is coated with polyurethane resin on at least one side. Proposed. (See Patent Document 2)
Japanese Patent Laid-Open No. 11-34258

  However, the biaxially stretched polyamide (nylon) film used in the lid material described in these patent documents is biaxially stretched sequentially or simultaneously with a tenter, and the longitudinal (MD) direction and lateral ( TD) The direction is different. Therefore, when the retort treatment is performed after filling and sealing the contents such as cooked rice, the container or lid material may be deformed, or when the lid material is peeled off from the obtained microwave oven cooking package and opened. There was a problem that a piece was cut and remained in a state where the lid was attached to the flange portion of the plastic container.

  Therefore, the present invention solves these problems of the prior art, peels the lid material from the microwave cooking packaging which is filled with contents such as cooked rice in a plastic container, heat sealed, sealed and retorted. It is an object of the present invention to provide a plastic container lid that does not break when the lid is opened.

  As a result of intensive studies, the present inventor has confirmed that the above problem can be solved by using a polyamide film produced by a simultaneous biaxial stretching method using a tubular method as a biaxially stretched polyamide resin intermediate layer constituting the cover material. Discovered and completed the present invention.

That is, in the present invention, the following configurations 1 to 6 are adopted.
1. Plastic container lid material comprising a laminate comprising a heat-sealable resin inner layer, a biaxially stretched polyamide resin intermediate layer produced by a simultaneous biaxial stretching method using a tubular method, and a gas barrier resin outer layer formed with an inorganic thin film layer .
2. 2. The plastic container lid according to 1, wherein the outer layer of the gas barrier resin is composed of a thermoplastic resin having a metal oxide vapor deposited film formed thereon.
3. 3. The plastic container lid material according to 2, wherein the thermoplastic resin is a polyester resin.
4). 4. The plastic container lid according to any one of 1 to 3, wherein the heat-sealable resin inner layer is composed of a polyolefin-based resin.
5. 5. The plastic container cover material according to any one of 1 to 4, wherein the plastic container is a container that is retorted after filling and sealing the contents.
6). The plastic container lid according to any one of 1 to 5, wherein the plastic container is a container that is cooked by a microwave oven in a state in which the contents are stored.

  According to the present invention, when the lid material is peeled off from the packaging for cooking a microwave oven, which is filled with contents such as cooked rice, heat-sealed and sealed and then retorted, the lid material is not cut off and is smoothly opened. It is possible to obtain a plastic container lid that can be opened. In addition, since the lid material of the present invention has no difference in properties in the vertical and horizontal directions, it is possible to prevent deformation of the plastic container and curling of the lid material when performing retorting after filling and sealing the contents. it can.

The present invention is characterized in that a polyamide film produced by a simultaneous biaxial stretching method using a tubular method is used as the biaxially stretched polyamide resin intermediate layer constituting the plastic container lid.
The biaxially stretched polyamide film can be produced by (1) biaxially stretching the film sequentially or simultaneously using a tenter, and (2) biaxially stretching the film extruded in the tubular shape by the tubular method. How to do is known.

  In the present invention, there is no difference in physical properties such as heat shrinkage rate and mechanical strength in the longitudinal and transverse directions, and the simultaneous biaxially stretched polyamide film by the tubular method is used as the intermediate layer of the cover material, thereby biaxially stretching by the tenter method. When a polyamide film is used as an intermediate layer of a lid material, the lid material is prevented from being cut off when the lid material is peeled off from the microwave cooking packaging and opened, thereby enabling smooth opening.

  The type of polyamide resin constituting the biaxially stretched polyamide intermediate layer is not particularly limited. For example, polycaprolactam (nylon 6), polyhexamethylene adipamide (nylon 66), polyhexamethylene sebacamide (nylon 610) , Polyaminoundecanoic acid (nylon 11), polylaurin lactam (nylon 12), polyxylene adipamide (MXD6), and mixtures thereof. Nylon 6 and nylon 66 are preferably used.

  The heat-sealable resin constituting the inner layer of the lid material of the present invention is not particularly limited. For example, known low density polyethylene, linear low density polyethylene, medium density polyethylene, high density polyethylene, polypropylene, propylene-ethylene copolymer Olefin resins such as olefin resins graft-modified with copolymers, ethylene-vinyl acetate copolymers, ethylenically unsaturated carboxylic acids or anhydrides thereof; polyamides or copolyamide resins having relatively low melting points or low softening points; Copolyester resin; polycarbonate resin or the like is used. Preferred heat-sealable resins include various polyolefin resins such as polyethylene and polypropylene.

Examples of the gas barrier resin on which the inorganic material thin film layer constituting the outer layer of the cover material is formed include, for example, a known silica-deposited polyester film, alumina-deposited polyester film, silica-deposited nylon film, alumina-deposited nylon film, alumina-deposited polypropylene film, carbon A film-deposited polyester film, a carbon film-deposited nylon film, and a binary-deposited film in which alumina and silica are simultaneously vapor-deposited on a base film such as a polyester film or a nylon film can be used.
As a particularly preferred gas barrier resin film, a film obtained by forming a metal oxide vapor deposition film such as silica or alumina on a polyester film such as polyethylene terephthalate (PET) can be cited. In these films, a protective layer may be provided on the deposited film by coating.

The lid material for a plastic container of the present invention includes the above-described heat-sillable resin inner layer, a biaxially stretched polyamide resin intermediate layer produced by a simultaneous biaxial stretching method using a tubular method, and a gas barrier resin outer layer formed with an inorganic material thin film layer It is comprised by the laminated body which laminated | stacked.
An adhesive layer and other intermediate resin layers can be interposed between the layers constituting the laminate as necessary. Such an adhesive is not particularly limited, and for example, a polyolefin adhesive modified with an acid anhydride such as maleic anhydride, a polyurethane adhesive, and the like, which are usually used as adhesives for laminates Either can be used.
There is no restriction | limiting in particular in the method of manufacturing a laminated body, Any normal methods, such as a dry lamination and an extrusion lamination, can be used.

As a material constituting the plastic container body having the flange portion, a plastic material having a heat seal property which is usually used for manufacturing a packaging container is used. As such a plastic material, for example, a single layer film or sheet made of a thermoplastic resin having heat sealability, a laminated film or sheet in which a thermoplastic resin having heat sealability is laminated with another thermoplastic resin, or the like Etc.
As the plastic material having such heat-sealability, the same material as the heat-sealable resin constituting the inner layer of the lid member described above can be used.

In addition, as other plastic materials to be laminated with the plastic material having heat sealability, thermoplastic resins with or without heat sealability, various barrier films, and oxygen-absorbing resins can be used.
Examples of such thermoplastic resins include crystalline polypropylene, crystalline propylene-ethylene copolymer, crystalline polybutene-1, crystalline poly-4-methylpentene-1, low-, medium-, or high-density polyethylene, Polyolefins such as ethylene-vinyl acetate copolymer (EVA), EVA saponified product, ethylene-ethyl acrylate copolymer (EEA), ion-crosslinked olefin copolymer (ionomer); polystyrene, styrene-butadiene copolymer, etc. Aromatic vinyl copolymers; halogenated vinyl polymers such as polyvinyl chloride and vinylidene chloride resins; polyacrylic resins; nitrile polymers such as acrylonitrile-styrene copolymers, acrylonitrile-styrene-butadiene copolymers; polyethylene Terephthalate, polytetramethylene terephthalate Polyesters such as nylon; polyamides such as nylon 6, nylon 12, metaxylylene adipamide (MXD6); various polycarbonates; fluororesins; thermoplastic resins such as polyacetals such as polyoxymethylene be able to. These thermoplastic resins can be used alone or in combination of two or more, and various additives such as oxygen absorbers may be blended and used.

As the barrier film, any film composed of a known thermoplastic resin having an oxygen barrier property can be used. Examples of such resins include ethylene-vinyl alcohol copolymers, polyamides, polyvinylidene chloride resins, polyvinyl alcohol, fluororesins, and the like, but do not contain chlorine that does not generate harmful gases during incineration. It is preferable to use a resin.
A particularly preferred oxygen barrier resin is an ethylene-vinyl acetate copolymer having an ethylene content of 20 to 60 mol%, particularly 25 to 50 mol%, and a saponification degree of 96 mol% or more, particularly 99 mol% or more. A saponified copolymer obtained by saponification to be
Other preferred oxygen barrier resins include polyamides in which the number of amide groups per 100 carbon atoms is in the range of 5 to 50, especially 6 to 20; for example, nylon 6, nylon 6,6, nylon 6 / 6,6 copolymer, metaxylylene adipamide (MXD6), nylon 6,10, nylon 11, nylon 12, nylon 13 and the like.

  Other barrier films include a gas barrier film in which an inorganic material thin film layer constituting the outer layer of the lid material described above is formed, a nylon 6 / metaxylylenediamine nylon coextruded film, and a polypropylene / ethylene-vinyl alcohol copolymer. Polymer coextruded film, polyvinyl alcohol coated polypropylene film, polyvinyl alcohol coated polyester film, polyvinyl alcohol coated nylon film, polyacrylic acid resin coated polyester film, polyacrylic acid resin coated nylon film, polyacrylic acid resin coated polypropylene Film, Polyglycolic acid resin coated polyester film, Polyglycolic acid resin coated nylon film, Polyglycolic acid resin coated polypropylene film An organic resin-coated film such as a beam, a further hybrid coating material formed of an organic resin material and an inorganic material and a polyester film or a nylon film, those that have been coated on the base film of the polypropylene film and the like, and the like. These barrier films can be used alone or in combination of two or more.

When the plastic container body is constituted by a laminate of two or more layers, an adhesive layer can be interposed between the respective layers as in the case of the lid material described above.
As a preferred layer structure of the laminate constituting the container body, for example, a gas barrier resin such as polypropylene (PP) / adhesive / ethylene vinyl acetate copolymer saponified product (EVOH) is sequentially formed from the outer layer side of the container. / Adhesive / PP; PP / adhesive / EVOH / adhesive / oxygen-absorbing resin layer (for example, polyolefin containing reducing iron and oxidation accelerator) / PP.

  Next, the plastic container lid material of the present invention will be further described with reference to the drawings. 1-2 is a figure which shows one example of the cover material for plastic containers of this invention, and FIG. 1 is a cross-sectional schematic diagram which shows the laminated constitution of a cover material. 2A is a plan view of a package body in which the lid material of FIG. 1 is heat-sealed to the flange portion of the plastic container, and FIG. 2B is a cross-sectional view of the package body of FIG. A schematic diagram is shown.

The lid 1 includes a heat-sealable resin inner layer 11, an adhesive layer 12, a biaxially stretched polyamide resin intermediate layer 13, an adhesive layer 12, and an inorganic material thin film layer 14 manufactured by a simultaneous biaxial stretching method using a tubular method. Is formed by laminating the gas barrier resin outer layer 15 having the structure. (See Figure 1)
As shown in FIG. 2, the lid 1 is heat-sealed to a flange portion 2 of a plastic container 3 filled with contents (not shown) such as cooked rice at a high temperature. The obtained package is subjected to retort processing and then distributed or stored.

In order to eat the contents of the package, the lid 1 is partially opened from the opening tab 5 provided at one corner of the lid 1 or a hole is made in the lid 1 with a pin or the like. After that, cook with a microwave. Then, after the cooking is finished, the lid 1 is opened from the opening tab 5 and the contents are eaten.
In this lid material 1, by using a simultaneous biaxially stretched polyamide film by a tubular method as a lid intermediate layer 13 with no difference in physical properties such as heat shrinkage and mechanical strength in the longitudinal and transverse directions, a conventional tenter is obtained. This prevents the lid from being broken when the biaxially stretched polyamide film is used as an intermediate layer of the lid material, thereby enabling smooth opening.

FIG. 3 is a view showing another example of the plastic container lid material of the present invention, and is a plan view of a package body in which the lid material is heat-sealed to the flange portion of the plastic container. In this lid material 1 ′, when heat-sealing to the flange portion 2 of the plastic container 3, the heat-sealing portion 4 protrudes in a U-shape toward the inside of the container at one corner portion, so that the microwave oven can be used. A steam vent seal portion 6 that automatically opens when cooked is formed. At the corner portion facing the steam release seal portion 6, the heat seal portion 4 is projected in a V shape in the container outer direction to form an opening portion 5 ′. Other configurations of the lid member 1 ′ are the same as those of the lid member 1 of FIG.
In this example, unlike the cover material of FIGS. 1 and 2, it is not necessary to partially open the cover material before cooking the package with a microwave oven.

EXAMPLES Next, the present invention will be further described with reference to examples, but the following specific examples are not intended to limit the present invention.
(Example 1)
A biaxially stretched polyester film outer layer 15 having a thickness of 12 μm having a transparent alumina vapor-deposited film 14, a polyurethane-based adhesive 12, a biaxially stretched polyamide resin intermediate layer 13 produced by a simultaneous biaxial stretching method by a tubular method having a thickness of 15 μm, A polyurethane adhesive 12 and a polypropylene film inner layer 11 made of an ethylene / propylene composite material having a thickness of 50 μm were laminated by dry lamination to produce a laminate for a lid material having the layer structure shown in FIG. The obtained laminate was cut into a desired size to form a plastic container lid.

On the other hand, in order from the outer layer, a polypropylene resin outer layer (thickness 400 μm) obtained by adding a titanium white pigment to polypropylene having a melt index (MI) 0.5 / adhesive layer (thickness 20 μm) made of maleic anhydride-modified polypropylene / ethylene- A barrier layer (thickness 60 μm) made of a vinyl alcohol copolymer / adhesive layer (thickness 20 μm) same as above / polypropylene resin inner layer (thickness 400 μm) of MI = 0.5 in a total of three types and five layers. A multilayer sheet having a thickness of 0.9 mm was produced by ordinary coextrusion molding. Using this multilayer sheet, a flanged rectangular container having the shape shown in FIG. 2 having a container outer dimension of 156 mm × 133 mm and a height of 29 mm (inner volume of about 340 ml) was formed by a normal vacuum / pressure forming machine.
Using a normal cooked rice production line, after filling the container with 200 g of cooked rice, heat sealing the lid material on the flange part of the container and performing retort treatment at 110 ° C. for 10 minutes. A package was produced.

(Comparative Example 1)
In Example 1 above, except that the biaxially stretched polyamide resin intermediate layer 13 of the lid material was obtained by sequentially biaxially stretching using a tenter and using a 15 μm thick biaxially stretched polyamide resin. In the same manner as in Example 1, a plastic container lid and a microwave cooking package were produced.

(performance test)
For each of the five cooked rice filling packages obtained in Example 1 and Comparative Example 1, the sealing strength of the lid member was evaluated by measuring the burst strength and the opening strength as follows. Moreover, the presence or absence of the cover breakage | opening at the time of opening the cover material 1 from the tab 5 for opening was confirmed visually. These results are shown in Table 1 below.

(Burst intensity)
Measured according to JIS Z 0238 “Testing method of heat-sealed soft packaging bag and semi-rigid container / burst strength test of container”.
(Opening strength)
Place the sealed container horizontally and attach the gripping part of the flange to the chuck (hook) of the push-pull gauge fixed horizontally. The tab 5 for opening the lid was grasped and opened at a speed of 3 m / min in the direction of 135 ° with respect to the flange, and the maximum value of the gauge was defined as the opening strength.

As can be seen from Table 1 above, no significant difference was found between Example 1 and Comparative Example 1 regarding the burst strength and opening strength of the lid, and there was no problem with the sealing performance of the lid of the present invention.
On the other hand, regarding the lid breakage at the time of opening, a clear improvement was observed in the lid material of the present invention. As a means for preventing the lid from being cut off, a method of reducing the opening force by reducing the sealing strength between the lid member and the container is conceivable. However, there is a risk of leakage of contents due to a decrease in sealing performance. In the lid material of the present invention, it is possible to prevent the lid from being cut at the time of opening and to smoothly open the lid material while maintaining the same sealing performance as the conventional lid material.
In each of the above examples, the example in which the lid member of the present invention is applied to a box-type container has been described, but it is needless to say that the lid member of the present invention can be applied to containers having other shapes such as cup-shaped containers. Moreover, in the Example, it showed by the example which retort-processes after filling and sealing of cooked rice, However, The lid | cover material of this invention is effective even when the retort process is not performed by aseptically filling the contents into a container.

It is a cross-sectional schematic diagram which shows an example of the cover material of this invention. It is a figure which shows the package body which heat-sealed the cover material of FIG. 1 to the plastic container. It is a figure which shows the other example of the cover material of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1, 1 'Cover material 2 Flange part 3 Container body 4 Heat seal part 5, 5' Opening part 6 Vapor release seal part 11 Heat sealable resin inner layer 12 Adhesive layer 13 Biaxially stretched polyamide resin intermediate layer 14 Inorganic substance thin film layer 15 Gas barrier resin outer layer

Claims (6)

  Plastic container lid material comprising a laminate comprising a heat-sealable resin inner layer, a biaxially stretched polyamide resin intermediate layer produced by a simultaneous biaxial stretching method using a tubular method, and a gas barrier resin outer layer formed with an inorganic thin film layer .   2. The plastic container lid according to claim 1, wherein the gas barrier resin outer layer is made of a thermoplastic resin having a metal oxide deposited film formed thereon.   The plastic container lid material according to claim 2, wherein the thermoplastic resin is a polyester resin.   The lid material for a plastic container according to any one of claims 1 to 3, wherein the heat-sealable resin inner layer is made of a polyolefin resin.   The plastic container lid according to any one of claims 1 to 4, wherein the plastic container is a container that is retorted after filling and sealing the contents.   The plastic container lid according to any one of claims 1 to 5, wherein the plastic container is a container that is cooked by a microwave oven in a state where contents are stored.

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