Stock material or miscellaneous articles – Structurally defined web or sheet – Including components having same physical characteristic in...
Reexamination Certificate
2001-02-28
2002-12-03
Tarazano, D. Lawrence (Department: 1773)
Stock material or miscellaneous articles
Structurally defined web or sheet
Including components having same physical characteristic in...
C428S215000, C428S359000, C428S516000
Reexamination Certificate
active
06489016
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a multilayer film for packaging based on polyolefin and, especially, to a multilayer film to be served, in particular, for various packaging uses, including prepackaging as used in supermarket or the like and heat-sealable packaging, which is superior in the material properties, such as transparency and heat-sealability, together with excellent performances in the clear-cutting, in the resistance to press-through and in the restorability from finger pressing.
DESCRIPTION OF THE RELATED TECHNIQUES
Plastic films have widely been employed for business uses in, such as supermarket and the like, for prepackaging various products including foods, such as vegetables and the like. Such prepackaging films serve for covering and enclosing commercial articles, such as foodstuffs, as naked piece as such or in a lot allotted or subdivided into small portions and piled or placed on a plastic carrier tray or the like. Thus, it is required for the prepackaging film that the film should be transparent and can easily be cut with an adequate extensible elasticity and an ability for adhering onto various surfaces, together with practical performances for attaining resistance to fogging on the inner face when packaged, resistance to break-through upon heat sealing due to the heated pressing by the sealing bars, restorability from finger pressing and superior heat-sealability.
Hitherto, films made of polymers based on polyvinyl chloride, ethylene/vinyl acetate copolymer and the like have found their uses for such packaging films. Among them, polymers based on polyvinyl chloride have requested recently to be replaced by materials having no chlorine content in view of the environmental hazard despite of their superior performances for such applications.
Japanese Patent Kokai Hei 4-246536 A discloses, as a packaging film having no chlorine content, a stretchable film of a multilayered structure prepared by laminating two outer layers which are constituted of a linear low density copolymer of ethylene/&agr;-olefin and a low density polyethylene and/or a copolymer of ethylene/vinyl acetate with an inner layer interposed therebetween which is constituted of a resin based on butene. While this multilayer film is superior in the transparency, extensible elasticity, clear cutting property etc., it brings about, however, a problem that it exhibits some insufficiencies in the ability for adhering onto various surfaces and in the heat-seal-ability. A countermeasure for remedying such a problem by incorporating a lower density resin for the outer layer will result in a decrease in the break-through resistance of the film upon heat-sealing, though the heat sealability may be increased thereby. When a more heat resistant polyethylene resin or a polypropylene resin is used for the intermediate layer for improving the thereby decreased break-through resistance, the restorability from finger pressing becomes decreased and finger press marks apt to be formed, since such a resin has usually a higher crystallinity.
As a packaging film made of a material having no chlorine content, there is disclosed in Japanese Patent Kokai Hei 8-66992 A (corresponding to U.S. Pat. No. 5,614,297) a stretchable polyolefin film produced by laminating an inner layer made of a composition composed of a first and a second ethylene/&agr;-olefin copolymers between the outer layers made of a composition composed of a first and a second ethylene/&agr;-olefin copolymers, wherein the first ethylene/&agr;-olefin copolymer has a density of 0.900-0.915 g/cm
3
and a melting point of 90° C. or higher and the second ethylene/&agr;-olefin copolymer has a density lower than 0.900 and a melting point lower than 80° C., respectively.
This film was proposed in order to attain a film having a low permanent strain by using a resin composition comprising an ethylene/&agr;-olefin copolymer of higher melting point and an ethylene/&agr;-olefin copolymer of lower melting point for the inner layer. However, it suffers from a problem that the material properties thereof will be a result of compromise between those of the component ethylene/&agr;-olefin copolymers due to the mutual solution resulting from the combination of these copolymers, whereby the break-through resistance to be expected from the higher melting copolymer and the restorability from finger press to be expected from the lower melting copolymer become both unsatisfactory.
As a packaging film made of a material having no chlorine content, there is disclosed in Japanese Patent Kokai Hei 8-119319 A a stretchable film for packaging foodstuffs, which comprises at least one layer of a resin mixture comprising, as the main components, a vinyl aromatic compound/conjugated diene copolymer and a polymer based on propylene and which exhibits a storage elastic modulus (E′) of 5.0×10
8
to 5.0×10
9
dyne/cm
2
and a loss factor (tan &dgr;) of 0.2-0.8.
By such a monolayer film of the resin mixture, however, a superior balance among the strength, clear-catting property and restorability from finger press can difficultly be attained.
SUMMARY OF THE INVENTION
The inventors have investigated the use of resins based on polyolefin as the material for multilayer packaging film and reached, from wide research of multilayer films permissible for employed practically and possessed of material properties comparable to those of the film based on polyvinyl chloride. The discovery that a multilayer packaging film exhibiting a better balance among the material properties and superior in transparency, in a property to be cut clearly, in the resistance to break-through and in the restorability from finger press was able to be attained by laminating layers each made of a specific resin composition, which has led to the present invention.
The object of the present invention is to provide a multilayer film for packaging made of polymers based on polyolefin exhibiting well balanced properties, which is superior in the transparency, in the clear cutting property, in the resistance to break-through and in the restorability from finger press together with an adequate stretchable elasticity and ability to adhere onto various surfaces.
The multilayer film for packaging according to the present invention comprises laminated outer layers and an inner layer interposed between the outer layers, wherein each of the outer layers is made of an outer layer resin composition selected from the group consisting of (I) and (II) given below and an inner layer is made of an inner layer resin composition comprising the resin components of both (III) and (IV) given below, with exclusion of the combination of an inner layer resin composition (III) comprising the component (E) with an inner layer resin composition (IV) comprising the component (H). The outer resin composition:
(I) A resin composition comprising
59.5-99.5% by weight of
(A) an ethylene/&agr;-olefin copolymer component which is composed of at least one copolymer of ethylene and an &agr;-olefin having 3-20 carbon atoms and which has a melt flow rate (MFR), determined at 190° C. under a load of 2.16 kg, of 0.1-10 g/10 min. and a density of not lower than 0.850 g/cm
3
and lower than 0.910 g/cm
3
,
0-40% by weight of
(B) a high pressure process low density polyethylene having a density of 0.915-0.930 g/cm
3
and 0.5-10% by weight of
(C) an anti-fogging agent.
(II) A resin composition comprising
99.5-90% by weight of
(D) an ethylene/vinyl acetate copolymer which is a copolymer of ethylene and vinyl acetate and has a vinyl acetate content of 10-30% by weight and a melt flow rate (MFR), determined at 190° C. under a load of 2.16 kg, of 0.5-30 g/10 min.
and 0.5-10% by weight of
(C) anti-fogging agent.
The inner resin composition:
(III) At least one resin component selected from the group consisting of
(E) a polymer based on ethylene which is a homopolymer of ethylene or a copolymer of ethylene and an &agr;-olefin having 3-20 carbon atoms and has a melt flow rate (MFR), determined at 190° C. unde
Burns Doane , Swecker, Mathis LLP
Mitsui Chemicals Inc.
Tarazano D. Lawrence
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