JP7497612B2 - Laminated lid material and packaging container - Google Patents

Description

The present invention relates to a laminated film, and more specifically, to a laminated lid material suitable for packaging containers that are to be retorted. It also refers to a packaging container that uses this laminated lid material.

As one mode of distribution of sanitary materials such as disposable contact lenses, a container is provided in a state where the lenses are immersed in a storage solution, and the container is opened and the lenses are removed from the storage solution when used. Since contact lenses require sterilization, the container containing the storage solution and the contact lenses may be sterilized by retort treatment after being sealed.
As the lid material for such containers, laminated films having gas barrier properties that block the intrusion of water vapor, oxygen, and other gases that can deteriorate the contents are used in order to prevent deterioration or spoilage of the contents and to maintain their functions and properties.

In the manufacture of laminated films with gas barrier properties, dry lamination is sometimes carried out using a urethane-based two-component curing adhesive. It is known that when such adhesives are attacked by alkaline substances, fragrances, surfactants, high-boiling organic solvents, etc. contained in the contents, the adhesive strength of the dry lamination decreases, causing delamination.

Regarding this issue, Patent Document 1 proposes an adhesive that is alcohol resistant.

Patent No. 5915710

In addition to alcohol, benzoic acid may be used as a preservative in preservatives for sanitary materials. Benzoic acid has a strong attack on adhesives, so when using sanitary materials that use such preservatives, it is necessary to consider resistance to benzoic acid in addition to retort treatment, and the structure described in Patent Document 1 is not sufficient.

In light of the above, the present invention aims to provide a laminated lid material that has sufficient resistance to retort treatment and benzoic acid.

A first aspect of the present invention is a laminated covering material comprising a base layer, an aluminum layer formed on the base layer, an adhesive layer formed on the aluminum layer, and an easy-peel layer formed on the adhesive layer.
In this laminated covering material, the adhesive layer has a main layer whose main component is maleic anhydride graft-polymerized polypropylene, and the Vicat softening point of the main layer is 110°C or higher and 114°C or lower .

The second aspect of the present invention is a packaging container comprising a resin container body and a laminated lid material according to the first aspect that is joined to the container body to seal the container body.

The laminated lid material of the present invention has sufficient resistance to retort treatment and benzoic acid.

1 is a cross-sectional view showing a schematic diagram of a packaging container provided with a laminated lid material according to one embodiment of the present invention. FIG. 2 is a schematic cross-sectional view of the laminated lid material.

An embodiment of the present invention will be described with reference to FIGS.
1 is a cross-sectional view showing a packaging container 100 including a laminated lid material 1 according to the present embodiment. The packaging container 100 includes a resin container body 101 and the laminated lid material 1 that seals the upper opening of the container body 101. The container body 101 is filled with a storage solution (contents) PF, and a contact lens CL is immersed in the storage solution PF.
The storage solution PF contains benzoic acid as a preservative. The packaging container 100 is sealed with the laminated lid material 1 and then retorted, whereby the storage solution PF and the contact lens CL contained in the container body are sterilized.

FIG. 2 shows a schematic cross-sectional view of the laminated covering material 1.
The laminated covering material 1 comprises a base layer 2 , an aluminum layer 3 , and an easy-peel layer 4 .

The base layer 2 may be, for example, a resin film.
As the resin for forming the resin film, polyester is suitable from the viewpoint of heat resistance and suitability for various processes, but is not limited thereto, and examples that can be used include polyolefin resins such as polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polyethylene-2,6-naphthalate, polybutylene terephthalate, and copolymers thereof; polyolefin resins such as polyethylene and polypropylene; polyamide resins such as nylon-6, nylon-66, and nylon-12; and hydroxyl group-containing polymers such as polyvinyl alcohol and ethylene-vinyl alcohol copolymers. These resins may be used alone or in combination of two or more.

The base layer 2 may be a stretched film or an unstretched film. Among them, a uniaxially stretched film or a biaxially stretched film is preferable, and a biaxially stretched film is more preferable, from the viewpoint of excellent mechanical strength and dimensional stability.
The substrate layer 2 may have a single layer structure made of one substrate film, or may have a multilayer structure in which two or more substrate films are laminated.

The thickness of the base layer 2 is not particularly limited, but may be, for example, 3 to 200 μm, and preferably 6 to 30 μm.
The base layer 2 has a printed layer 5 on one surface. The printed layer 5 can appropriately include information about the contents, various patterns, and the like. In Fig. 2, the printed layer 5 is formed on the surface on the container body 101 side, but it may be formed on the opposite surface or on both surfaces. Furthermore, the printed layer 5 may be omitted.

The aluminum layer 3 has a gas barrier function. The aluminum layer 3 can be made of aluminum foil or an aluminum vapor deposition layer. In this embodiment, the aluminum layer 3 is formed by bonding the aluminum foil to the print layer 5 with an adhesive layer 6. The adhesive layer 6 can be made of various types of adhesives for dry lamination, such as a two-component adhesive made of a polyol component and an isocyanate component.

The easy peel layer 4 bonds the laminated lid material 1 and the container body 101 to maintain the sealed state of the packaging container 100 and to facilitate the opening operation. As the easy peel layer 4, any of various known easy peel sealant films (polypropylene-based, etc.) can be appropriately selected and used.
The easy peel layer 4 is bonded to the aluminum layer 3 by an adhesive layer 7. The easy peel layer 4 can be bonded by extrusion lamination, in which a resin that will become the adhesive layer 7 is extruded as a single layer or co-extruded.

The adhesive layer 7 has a main layer mainly composed of maleic anhydride graft-polymerized polypropylene (hereinafter referred to as "modified PP") on the side in contact with the aluminum layer 3. The adhesive layer 7 may be a single main layer, or may have another layer on the side of the easy-peel layer 4. An example of the material of the other layer is unmodified polypropylene.
Modified PP is polypropylene graft-modified with maleic anhydride. Examples of polypropylene in modified PP include homopolypropylene, block polypropylene, random polypropylene, propylene-α-olefin copolymer, etc. Examples of α-olefin include ethylene, 1-butene, etc.

After various studies on the composition of a laminated lid material that is highly resistant to retort treatment and benzoic acid, the inventors found that it is preferable to use modified PP for the adhesive layer 7. Further studies showed that the effect is more pronounced when the maleic anhydride graft of the modified PP is 0.1 weight percent (wt%) or more and 1 wt% or less. If the maleic anhydride graft rate is less than 0.1 wt%, sufficient adhesive strength with the aluminum layer 3 cannot be obtained, and there is a high possibility that delamination will occur during sterilization, etc. On the other hand, if the maleic anhydride graft rate exceeds 1 wt%, the resin properties become unstable. Specifically, the reaction catalyst used during grafting promotes the decomposition of the PP resin itself, resulting in a smaller molecular weight and an extremely increased melt flow rate (MFR), and the film-forming suitability is lost. As a result, the film strength of the formed adhesive layer decreases, and there is a possibility that a defect in which sufficient adhesive strength cannot be obtained occurs.

When the packaging container 100 is retorted, the adhesive layer 7 is softened by high temperature. When the adhesive layer 7 is softened, it flows between the aluminum layer 3 and the easy-peel layer 4, and cannot withstand the increase in internal pressure in the container body 101, causing the sealed state to be broken.
The inventors have conducted various studies on this phenomenon and found that the melting point is not a very suitable index for selecting the material of the adhesive layer 7, but the Vicat softening point is a suitable index. In other words, even if the melting point is sufficiently high relative to the temperature during retort treatment, if the Vicat softening point is low, the material will flow even if it is not melted, and therefore the sealed state cannot be maintained sufficiently.

The inventors' research has revealed that if the Vicat softening point of the layer mainly composed of modified PP is 110°C or higher, this is close enough to the temperature of the retort treatment, so that the layer mainly composed of modified PP does not flow excessively during the retort treatment, and the sealed state is easily maintained. The method for measuring the Vicat softening point is specified in JIS K7206:2016 (ISO306:2013).

The thickness of the adhesive layer 7 is preferably 1 to 30 μm, and more preferably 1 to 15 μm. When the thickness of the adhesive layer 7 is equal to or greater than the lower limit, it is easy to prevent delamination between the aluminum layer 3 and the easy-peel layer 4. When the thickness of the adhesive layer 7 is equal to or less than the upper limit, excellent thermal conductivity is achieved in the lamination process after stacking, and appropriate laminate strength is obtained.
The main layer of the adhesive layer 7 may contain other resins as long as the main component is modified PP. An example of a resin other than modified PP used in the adhesive layer 7 is unmodified polypropylene.

The resin forming the container body 101 may be any resin capable of bonding to the easy peel layer 4, and a resin of the same type may be selected to match the easy peel layer 4.

The storage solution PF and contact lens CL are placed in the container body 101, and the laminated lid material 1 is placed with the easy peel layer 4 facing the container body 101. The contact area between the laminated lid material 1 and the container body 101 is then heated and pressurized, and the laminated lid material 1 is bonded to the container body, completing the packaging container 100 with the inside of the container body 101 sealed.

Since the laminated lid material 1 has the above-mentioned configuration, even when the preservative solution PF contains benzoic acid and the manufactured packaging container 100 is sterilized by retort treatment, the sealed state is suitably maintained and delamination (peeling) between the aluminum layer 3 and the easy-peel layer 4 is suitably suppressed. As a result, even in an environment of 120° C., which is almost the same temperature as that during retort treatment, the laminate strength between the aluminum layer 3 and the adhesive layer 7 can be made 2.0 N/15 mm or more.
The laminated lid material 1 and the packaging container 100 including the same are suitable for packaging various sanitary materials that contain benzoic acid or require sterilization. In addition, dry lamination is not required, and the bonding strength increases with retort treatment, so no curing process is required during production, and production efficiency is high.

The laminated lid material and packaging container of the present invention will be further explained using examples. The technical scope of the present invention should not be narrowly interpreted based solely on the following description.

Example 1
A 16 μm thick polyester film (FE2001 manufactured by Futamura Chemical Co., Ltd.) was prepared as a substrate layer. A 50 μm thick aluminum foil was attached to one side of the substrate layer by dry lamination using an adhesive consisting of an ester main chain base agent and a curing agent, to form an adhesive layer and an aluminum layer.
A 30 μm thick sealant film (Toray Film Processing Co., Ltd. 9501H) was used as the easy peel layer, and an adhesive layer and an easy peel layer were formed on the aluminum layer by extrusion lamination. Two types of resins, modified PP (A) (melting point peak: 141° C., density: 0.90 g/cm ³ , MFR: 15 g/10 min) and unmodified random polypropylene, were used as the adhesive layer. The thickness of each layer was 12 μm, and the main layer made of modified PP was placed on the aluminum layer side.
In this manner, the laminated lid material according to Example 1 was produced.

Example 2
The laminated lid material of Example 2 was produced in the same manner as in Example 1, except that modified PP (B) (melting point peak 104, 135°C, density 0.895 g/ ^cm3 , MFR 9.2 g/10 min) was used instead of modified PP (A).

(Comparative Example 1)
The laminated lid material of Example 2 was prepared in the same manner as in Example 1, except that modified PP (C) (melting point peak: 103, 135°C, density: 0.88 g/cm ³ , MFR: 10.3 g/10 min) was used instead of modified PP (A).

(Comparative Example 2)
The laminated lid material of Example 2 was prepared in the same manner as in Example 1, except that modified PP (D) (melting point peak: 100, 155°C, density: 0.88 g/cm3, MFR: 8.5 g/10 min) was used instead of modified PP ( ^A ).

The laminated covering materials of each of the Examples and Comparative Examples were used to carry out the following evaluations.
(Measurement of Vicat softening point)
The Vicat softening point of the main layer made of modified PP was measured based on ISO 306: 2013. The measurement was performed by preparing a thick sample made of only the main layer.

(Measurement of Laminate Strength)
A test piece having a width of 15 mm was cut out from each of the laminated lid materials. The laminate strength between the aluminum layer and the adhesive layer was measured at 120° C. using a tensile tester in accordance with JIS-K6854.

(Holding tight against benzoic acid-containing contents and retort processing)
A PP container body was filled with 0.6 mL of a saturated benzoic acid aqueous solution, and the laminated lid material of each example was joined by heat fusion to seal the container body. In this way, a packaging container according to each example was produced.
After each packaging container was subjected to retort sterilization at 121°C for 30 minutes, a hole was made in the container body to remove the saturated benzoic acid aqueous solution, and ink was injected. The joint between the laminated lid material and the container body was visually checked for the presence or absence of ink leakage.
The evaluation was made on a two-level scale: ".largecircle." (good) indicates that no leakage occurred, and "x (bad)" indicates that leakage occurred.

The results are shown in Table 1.

As shown in Table 1, in each embodiment in which the Vicat softening point of the modified PP of the main layer in the adhesive layer was 110°C or higher, the laminate strength between the aluminum layer and the adhesive layer in an environment of 120°C was high, and leakage after retort treatment was prevented.
On the other hand, in the comparative example in which the Vicat softening point of the modified PP of the main layer was 110° C. or less, the laminate strength was insufficient in an environment of 120° C. In addition, the sealed state could not be maintained after the retort treatment, and leakage occurred.
Since no difference was observed in the laminate strength after retort treatment between the Example and the Comparative Example, it was speculated that the route of leakage was caused by the modified PP of the Comparative Example becoming too soft during retort treatment. This is a new finding that cannot be found by simply measuring the laminate strength of the finished product.

The above describes one embodiment of the present invention and examples, but the technical scope of the present invention is not limited to the contents of the above embodiment, etc., and various modifications and deletions can be made to each component without departing from the spirit of the present invention.

1 Laminated lid material 2 Base material layer 3 Aluminum layer 4 Easy peel layer 7 Adhesive layer 100 Packaging container 101 Container body PF Storage liquid (contents)

Claims (4)

A base layer;
an aluminum layer formed on the base layer;
an adhesive layer formed on the aluminum layer;
an easy peel layer formed on the adhesive layer;
Equipped with
the adhesive layer has a main layer on the aluminum layer side, the main layer being composed mainly of maleic anhydride graft-polymerized polypropylene, and the Vicat softening point of the main layer is 110° C. or higher and 114° C. or lower ;
Laminated lid material. The laminate strength between the aluminum layer and the adhesive layer measured in accordance with JIS-K6854 in a 120°C environment is 2.0 N/15 mm or more.
The laminated covering material according to claim 1. A resin container body;
The laminated lid material according to claim 1 or 2, which is joined to the container body to seal the container body;
Equipped with
Packaging container. The contents contained in the container body contain benzoic acid.
The packaging container according to claim 3.

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