Laminates

Details Laminates Laminates

1998-04-08

2001-09-25

Copenheaver, Blaine (Department: 1775)

Stock material or miscellaneous articles

Composite

Of addition polymer from unsaturated monomers

C428S516000, C428S461000, C428S511000, C525S240000

Reexamination Certificate

active

06294266

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to useful laminates which are particularly excellent in adhesive properties to metallic foil such as aluminum foil, deposited metal surfaces of metal-deposited films and surfaces of other sandwich base materials and in tear properties such an unsealing properties and have low small and high strength as packaging films.
BACKGROUND OF THE INVENTION
Laminates which are prepared by sandwich extrusion laminating of a base material such as various re s in film undergoing anchor coat treatment or cellophane and metallic foil or a metal-deposited resin film with a low-density polyethylene resin followed again by extrusion laminating the low-density polyethylene resin have been used as packaging films for various purposes.
About the extrusion laminating as a method of laminating which makes it possible to attain the degree to which the adhesive strength between a bonding layer and metal foil in a laminate meets practical purposes, there is a report (
Convertech
(8), page 36, 1991) on a method for producing laminates, in which an extrusion resin temperature of a low-density polyethylene having good workability is set, for example, at a temperature as high as 320° C. or above to oxidize the resin surface within the air gap between the die and pressure roller and the bonding layer as thin as 10 to 15 &mgr;m in coat thickness is allowed to adhere to metal foil's surface. However, the adhesion strength is as weak as 50 to 100 g/15 mm wide and the polyethylene elongates on unsealing of a package, being difficult to tear, because of the weak adhesion to metal. In addition, packaging of viscous, aqueous and heavy articles which requires high pressure resistance to packaging films is quite impossible.
Anchor coat treatment on metallic foil's surfaces may be considered as a means of improving the adhesion strength. However, the anchor coat treatment and extrusion laminating of a single sheet of metal foil as thin as 7 to 12 &mgr;m cause tears or creases in the sheet, which makes practical work impossible. JP-A-4-368845 (The term “JP-A” as used herein means an “unexamined published Japanese patent application”) reports a method of extrusion laminating of a resin containing polar groups such as an ethylene/acrylic acid copolymer resin and a method of extrusion laminating of an ethylene copolymer resin undergoing ozone treatment which is prepared by copolymerization of ethylene, an unsaturated polybasic acid and an unsaturated monomer selected from lower alkyl esters and vinyl esters of acrylic acid. However, these copolymer resins are unpreferred because of high manufacturing cost, complicated exchange of resins in an extruder and, in addition, smell of the films. When a customary CPP film or a film in which a thin film of silicon oxide is formed at least on one side of a transparent base material is sandwich laminated, the surface of the CPP film or one side of the film having a thin silicon oxide film formed undergoes anchor coat treatment prior to the laminating. In these cases, the films are unpreferred because of high manufacturing cost and smell thereof.
In these situations, a costly method using an adhesive, called “dry laminating,” has been unavoidably adopted when strength is required as in packaging bags.
SUMMARY OF THE INVENTION
The present invention is to provide laminates excellent in adhesion strength, in which metal-deposited films or metal foil used as sandwich base materials need not undergo anchor coat treatment on the respective deposited surfaces or surface of the foil, and resin compositions comprising an ethylene/&bgr;-olefin copolymer resin with low smell which also is a good purging material are used for a bonding layer; and the resin compositions.
The present invention is characterized by the laminates in which the laminates are formed by laminating at least a base material and s sandwich base material via a bonding layer, the adhesion strength between the sandwich base material and the bonding layer is 200 g/15 mm wide or more (at 23° C.), and in addition, the bonding layer is formed of the resin compositions comprising the ethylene/&bgr;-olefin copolymer resin.
DETAILED DESCRIPTION OF THE INVENTION
In the present invention, it is important for the resin compositions forming the bonding layer to have the following physical properties.
1. MPR
The resin compositions for the bonding layer may be from 1 to 100 g/10 minutes, and preferably from 3 to 50 g /10 minutes in MFR (melt flow rate) as defined by JIS-K7210. When the MFR falls to reach the specified range, the adhesion strength to metal foil's surfaces, the deposited metal surfaces of metal-deposited films, or other sandwich base materials (Hereinafter merely referred to as the “adhesion strength to sandwich base materials”) is insufficient, and the resins lose ductility and malleability. The MFR exceeding the range results in increasing neck-in. In either case, uniform fused films can not be obtained.
2. Density
The resin compositions for use in the bonding layer may be 0.912 g/cm
3
or less, and preferably 0.900 g/cm
3
or less in density an defined by JIS-K7112. The lower limit of the density of the resin composition is preferably 0.87 g/cm
3
. The density exceeding the specified range results in reducing the adhesion strength to sandwich base materials, failing to form laminates having high heat-sealing strength and high pressure resistance required for use as packaging films.
In the present invention, the ethylene/&agr;-olefin copolymer resins used as an indispensable component to the resin compositions are prepared by copolymerization of ethylene with &agr;-olefin, and preferably &agr;-olefin having 3 to 10 carbon atoms such an propylene, butene-1, hexene-1, octene-1, and 4-methylpentene-1. The &agr;-olefin can be used alone or as mixtures of 2 or more kinds thereof. It is important for the copolymer resins to have the following physical properties.
1 MFR
The ethylene/ &agr;-olefin copolymer resins as used herein may be from 1 to 100 g /10 minutes, and preferably from 3 to 50 g/10 minutes in MFR as defined by JIS-K7210. The MFR not reaching the specified range results in lowering the adhesion strength to sandwich base materials and causes the copolymer resins to lose ductility and malleability. On the other hand, the MFR exceeding the specified range results in increasing the neck-in. In either case, uniform fused films can not be obtained.
2 Density.
The ethylene/&agr;-olefin copolymer resins as used herein may be 0.900 g/cm
3
or less, and preferably 0.890 g/cm
3
or less in density as defined by JIS-K-7112. The lower limit of the density of the ethylene/&agr;-olefin copolymer is preferably 0.86 g /cm
3
. The density exceeding the specified range results in lowering the adhesion strength to the sandwich base materials, failing to form laminates exhibiting high heat-sealing strength and high pressure resistance required for use as packaging films.
The ethylene/&agr;-olefin copolymer resins as used in the present invention include both of those prepared in the presence of metallocene catalysts (hereinafter referred to as “metallocene materials”) and those prepared in the presence of vanadium catalysts (hereinafter referred to an “vanadium materials”). However, the metallocene materials are preferred.
The metallocene materials are prepared according to procedures as described in JP-A-58-19309, JP-A-59-95292, JP-A-60-35005, JP-A-60-35006, JP-A-60-35007, JP-A-60-35008, JP-A-60-35009, JP-A-61-130314, JP-A-3-163008, European Patent Publication No. 420,436, U.S. Pat. No. 5,055,438, and PCT International Publication No. WO91/04275. That is, the metallocene materials are prepared by copolymerization of ethylene as a main component with &agr;-olefin having 3 to 10 carbon atoms as a sub-component in the presence of a metallocene catalyst, a metallocene/alumoxane catalyst, or a catalyst comprising a metallocene compound and a compound forming a stable ion by reaction with the metallocene catalyst as disclosed in PCT International Publication No. WO92/07123.

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