Multi-layer container structure

Stock material or miscellaneous articles – Hollow or container type article – Polymer or resin containing

Reexamination Certificate

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C428S216000, C428S363000, C428S402000

Reexamination Certificate

active

06723403

ABSTRACT:

BACKGROUND OF THE INVENTION
(i) Field of the Invention
The present invention relates to a multi-layer structure, a container using the same, and its manufacturing method. More specifically, it relates to a multi-layer structure suitable for the manufacture of containers particularly in a packing field, a container which can be obtained by the use of this multi-layer structure, can be used for the packing of foods, drugs, cosmetics and the like and which has excellent sealing properties and easy opening properties, and a method for efficiently manufacturing the container.
(ii) Description of the Invention
Particularly in carrying out the packing of drugs, foods, cosmetics and the like, these contents are filled into containers, and after sealing, they are heated for sterilization by boil, retort, microwave or the like. At this time, the breakage of the containers and the deterioration of a container material occur on occasion owing to expansion by the heating and the like. In addition, when the sealing properties of the containers are increased for the sake of the breakage prevention of the containers, the opening of the containers tends to be difficult. Therefore, it has been desired to improve the sealing properties or to prevent the deterioration, keeping up the opening properties.
In order to improve the sealing properties and to keep up the easy opening properties at a high temperature, it has been suggested to use heat-resistant resins for an innermost layer (a surface layer) and an intermediate layer under the innermost layer, and for example, Japanese Patent Application Laid-open No. 230120/1996 has disclosed a laminate which is constituted of an innermost layer comprising a polypropylene resin, an intermediate comprising a mixture of 20 to 90% by weight of a polypropylene and 80 to 10% by weight of a 4-methylpentene-1 resin, and a base layer comprising a polypropylene resin. However, such a laminate is expensive, and it has a drawback that at the time of the thermoforming of containers, the molding is difficult. Moreover, it is also difficult to mold films from the molding multi-layer structure by co-extrusion, depending on the constitution of the resins.
On the other hand, in Japanese Patent Application Laid-open No. 71824/1994, there has been disclosed a container in which a base layer, an adhesive layer, a polypropylene, a polyethylene and a polypropylene are laminated in this order on an outer layer, and the container having flanges is molded by the use of composite sheets having an interlaminar adhesive force relation of X<Y wherein X is an interlaminar adhesive force between the polypropylene layer as an innermost layer and the adjacent polyethylene layer, and Y is an interlaminar adhesive force between the polyethylene layer and the polypropylene layer constituting the outside of the polyethylene layer, and after the filling of contents, the container is sealed up with a lid so that an inter-laminar adhesive force Z between the lid and the polypropylene layer as the innermost layer of the flanges may be Z>X. In this container, the innermost layer is made of the polypropylene to improve heat resistance, and therefore the deterioration of the base material can be prevented. In addition, the seal layer and the opening layer are separately formed to improve the opening properties. However, the disclosed container has a drawback that sealing properties at the time of heating are poor because of the intermediate layer being the polyethylene layer.
Furthermore, Japanese Patent Application Laid-open No. 29324/1990 had disclosed a multi-layer structure in which an interlaminar peeling strength is suitably regulated by the use of a thermoplastic resin containing a flaky inorganic filler as an intermediate layer. However, this multi-layer structure has a drawback that the opening properties are bad when the surface layer is thick, and the sealing properties at heating are poor when the intermediate layer is thin.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a multi-layer structure which can suitably be used to manufacture containers in which sealing properties are improved for the prevention of container breakage during sterilization by heating, cooking by heating, distribution or the like and heat resistance is improved for the prevention of container deterioration and which is excellent in opening properties.
Another object of the present invention is to provide a container comprising this multi-layer structure and having the above-mentioned excellent characteristics.
Still another object of the present invention is to provide a method for efficiently preparing the above-mentioned container.
The present inventors have intensively researched to achieve the above-mentioned objects. As a result, it has been found that the above-mentioned objects can be achieved by a multi-layer structure having two or more layers in which an interlaminar peeling strength between a surface layer and an adjacent layer is in a specific range, particularly a multi-layer structure which comprises a base layer, an intermediate layer having a specific thickness and a surface layer mainly comprising a polypropylene resin and having a specific thickness on the base layer and in which each interlaminar peeling strength meets specific conditions, and a container comprising this multi-layer structure. Furthermore, the present inventors have also found that when thermoforming is carried out by pressing portions, which will become flanges of the molded container, under a specific pressure, the desired container can efficiently be obtained.
The present invention has been completed on the basis of such knowledge.
That is to say, aspects of the present invention are as follows.
(1) The first aspect of the present invention is directed to a multi-layer structure having two or more layers which comprises a surface layer (a) comprising a thermoplastic resin and having a thickness of 10 to 80 &mgr;m and an adjacent layer (b) comprising a thermoplastic resin or a thermoplastic resin containing an inorganic filler, an interlaminar peeling strength between the surface layer (a) and the adjacent layer (b) being in the range of 0.3 to 2.0 kg/15 mm (hereinafter referred to as “the multi-layer structure I”).
(2) The second aspect of the present invention is directed to the multi-layer structure according to the above-mentioned first aspect wherein an intermediate layer (B) comprising a thermoplastic resin containing 20 to 70% by weight of a platelike inorganic filler and having a thickness of 50 &mgr;m or more and a surface layer (A) comprising a thermoplastic resin containing 60 to 100% by weight of a polypropylene resin and having a thickness of 10 to 80 &mgr;m are laminated in this order on a base layer (C); an interlaminar peeling strength [(A)/(B)] between the surface layer (A) and the intermediate layer (B) is in the range of 0.3 to 2.0 kg/15 mm; and an interlaminar peeling strength [(B)/(C)] between the intermediate layer (B) and the base layer (C) satisfies a relation of [(A)/(B)]<[(B)/(C)] (hereinafter referred to as “the multi-layer structure II”).
(3) The third aspect of the present invention is directed to a container comprising the multi-layer structure I described in the above-mentioned first aspect (hereinafter referred to as “the container I”).
(4) The fourth aspect of the present invention is directed to a container comprising the multi-layer structure II described in the above-mentioned second aspect (hereinafter referred to as “the container II”).
(5) The fifth aspect of the present invention is directed to a method for manufacturing a container which comprises the steps of heating the multi-layer structure described in claim
1
, and then thermoforming the container by pressing portions, which will become flanges of the molded container, under a press pressure of 1.0 to 10.0 kg/cm
2
.
(6) The sixth aspect of the present invention is directed to a container manufactured by the method described in the fifth aspect of the p

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