Stock material or miscellaneous articles – Web or sheet containing structurally defined element or... – Physical dimension specified
Reexamination Certificate
2003-01-13
2004-09-21
Nakarani, D. S. (Department: 1773)
Stock material or miscellaneous articles
Web or sheet containing structurally defined element or...
Physical dimension specified
C428S213000, C428S215000, C428S516000
Reexamination Certificate
active
06794029
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a layered film which exhibits, when used as a sealant film, excellent openability, good clouding property (the “clouding” as used herein means the “whitening”), high water vapor barrier property and superior seal strength stability and which is suitable as a medical packaging material, and also relates to a packaging product thereof.
In particular, the layered film of the present invention is suitable as a sealant film for a packaging product which is produced through knurl-sealing, such as a packaging product for a blood sugar measuring electrode.
This application is based on Japanese Patent Application No. 2000-217338, Japanese Patent Application No. 2001-188658 and U.S. Provisional Patent Application No. 60/249,291, the contents of which are incorporated herein by reference.
BACKGROUND ART
Heretofore, polyolefin film is used as various food or medical packaging materials by making use of its characteristic features such as inexpensivenss, resistance against heat or chemicals and easy heat sealability.
In the food packaging material, an aluminum foil, a saponified product of ethylene-vinyl acetate copolymer resin and vinylidene chloride resin are used as a gas barrier layer, the gas barrier layer is combined with a polyamide resin layer, a polyester resin layer and the like, and a polyolefin-base resin such as polypropylene or polyethylene is used as a heat seal layer. Also in the medical packaging material, a polyolefin-base resin is used as a heat seal layer.
With respect to the easily openable sealant film, a method of using a resin composition obtained by mixing polypropylene and polyethylene for the sealant layer, and a method of using a resin obtained by graft-polymerizing styrene to a polyolefin-base resin are known.
In the sealant film for a packaging product which is produced through knurl-sealing, such as a packaging product for a blood sugar measuring electrode, a resin composition obtained by mixing a linear low-density polyethylene with a low melting point polypropylene has been heretofore used for the sealant layer and thereon, a homopolypropylene as a substrate layer is stacked.
The sealant film is characterized in that when the packaging product is opened, the heat sealed portion is clouded (“the heat sealed portion is clouded” as used herein means that the heat sealed portion is whitened) and therefore, it can be confirmed that the packaging product was infallibly heat-sealed.
However, the sealant film has a problem in that since the heat seal strength is as high as 1,200 g/15 mm-width or more, opening is difficult; since the latitude of the heat seal temperature is narrow, the knurl-sealing machine fails in controlling the temperature; or when the heat seal pressure fluctuates, homopolypropylenes are heat-sealed with each other and opening cannot be attained.
Examples of the easily openable sealant film include a packaging product having a heat sealable resin layer which comprises a resin composition layer having a thickness of 5 to 25 &mgr;m and containing a crystalline polypropylene-base resin having a melt index of 2 to 100 (g/10 min) and a polyethylene having a melt index of 2 to 50 (g/10 min) in a weight ratio of 50:50 to 95:5 (see, JP-A-58-1672 (the term “JP-A” as used herein means an “unexamined published Japanese patent application”)), an easily openable drop lid comprising three layers of an uppermost layer formed of a heat-resistant resin layer, an intermediate layer formed of a polypropylene and a cohesive failure sealant layer provided under the intermediate layer and formed of a polypropylene-polyethylene blend polymer (see, JP-U-B-61-37647 (the term “JP-U-B” as used herein means an “examined Japanese utility model publication”)), a container comprising a film layer formed of a blend material of a base resin comprising a crystalline polypropylene or a crystalline propylene-ethylene copolymer with from 8 to 30 wt % of an ethylene-vinyl acetate copolymer having a vinyl acetate content of 8 to 5 wt %, where the heat seal strength after the thermal sterilization is 100 to 1,700 g/cm (see, JP-A-57-28777), and a composite film comprising a propylene-base resin layer and a resin composition layer containing a propylene-ethylene random copolymer and/or a propylene-ethylene-butene-1 ternary copolymer, and a high-pressure polyethylene and/or a linear low-density polyethylene (see, JP-A-63-179741).
These sealant films have a problem in that the low-temperature heat sealability is inferior, the opening strength is too strong or the heat seal portion shows poor clouding or is not clouded at all at the time of opening.
Examples of the case using a combination of a polyethylene and a polybutene-1 as in the present invention include a method of blending a polyethylene and a polybutene-1 for preventing distortion and cracking of a polyethylene-made bottle, pipe, electric wire coating or the like due to contact with a viscous liquid (see, JP-B-39-22351 (the term “JP-B” as used herein means as an “examined Japanese patent publication”)). However, this publication neither discloses nor suggests the object of the present invention or the method for solving the problems described in the present invention.
The object of the present invention is to provide a layered film which exhibits excellent openability, good clouding property, high water vapor barrier property and superior seal strength stability as compared with conventional films, and which is suitable as a food or medical packaging material fitted to knurl-sealing, and a packaging product using said layered film.
DISCLOSURE OF INVENTION
As a result of extensive investigations, the present inventors have found that the above-described object can be attained by stacking a specific resin composition layer and a high-density polyethylene layer. The present invention has been accomplished based on this finding.
More specifically, the layered film of the present invention comprises at least two layers of a resin composition layer [layer (A)] comprising (a) from 60 to 90% by weight of a linear low-density polyethylene produced using a single site catalyst and (b) from 40 to 10% by weight of a polybutene-1, and a high-density polyethylene layer [layer (B)] comprising (c) a high-density polyethylene having a density of 0.950 to 0.970 (g/cm
3
).
The linear low-density polyethylene of the layer (A) has a density of 0.890 to 0.935 (g/cm
3
) and a melt flow rate of 2 to 20 (g/10 min).
The high-density polyethylene (c) of the layer (B) has a melt flow rate of 1 to 15 (g/10 min).
The layered film is produced by forming a film at an extrusion temperature of 160 to 250° C. and cooling the film at a cooling temperature of 40 to 80° C.
The packaging product of the present invention comprises sealant layers, wherein one sealant layer is a layer (A) of a layered film comprising at least two layers of a resin composition layer [layer (A)] comprising (a) from 60 to 90% by weight of a linear low-density polyethylene produced using a single site catalyst and (b) from 40 to 10% by weight of a polybutene-1, and a high-density polyethylene layer [layer (B)] comprising (c) a high-density polyethylene having a density of 0.950 to 0.970 (g/cm
3
).
In the packaging product of the present invention, one sealant layer is the layer (A) of said layered film comprising at least two layers of the layer (A) and the layer (B) and another sealant layer is a linear low-density polyethylene layer [layer (C)] comprising (d) a linear low-density polyethylene, which is produced using a single site catalyst, having a density of 0.890 to 0.925 (g/cm
3
) and a melt flow rate of 2 to 10 (g/10 min).
In the packaging product of the present invention, one sealant layer is the layer (A) of said layered film comprising at least two layers of the layer (A) and the layer (B), and another sealant layer is a layer (C) of a layered film comprising at least two layers of a linear low-density polyethylene layer [layer (C)] comprising (d) a linear low-density poly
Nasu Takao
Watanabe Kazuyuki
Nakarani D. S.
Showa Denko Plastic Products Co., Ltd.
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