Sealable film

Details Sealable film Sealable film

2002-01-11

2004-03-16

Chen, Vivian (Department: 1773)

Stock material or miscellaneous articles

Structurally defined web or sheet

Including components having same physical characteristic in...

C428S035700, C428S036600, C428S217000, C428S343000, C428S346000, C428S347000, C428S349000, C428S3550EN, C428S3550AC, C428S515000, C428S516000, C428S518000, C428S520000, C428S522000, C428S523000

Reexamination Certificate

active

06706377

ABSTRACT:

FIELD OF THE INVENTION
The invention relates to a thermoplastic film which is peelable and sealable. More specifically, the invention relates to a thermoplastic film with intermediate separable layers sandwiched between a core layer and a sealing layer which permits peeling of the core layer from the seal layer. The film also provides improved optical clarity.
BACKGROUND OF THE INVENTION
A peelable film structure is described in WO 96/04178 published on Feb. 15, 1996. The film structure comprises a core layer comprising an olefin polymer and a heat sealing layer comprising a blend of low density polyethylene (LDPE) and a material incompatible with the LDPE, such as an olefin polymer or co- or terpolymer of ethylene, propylene or butene. The film structure can be heat sealed to a plastic container to form the lid of the container, or to itself to form a package. It is disclosed that when used with a plastic container, the film structure can be readily peeled from the container in order to open it.
In U.S. Pat. No. 5,358,792 a heat sealable composition is described comprising (a) from about 30 to about 70 weight percent of a low melting polymer comprising a very low density ethylene based copolymer defined by a density in the range of about 0.88 g/cm
3
to about 0.915 g/cm
3
, a melt index in the range of about 1.5 dg/min to about 7.5 dg/min, a molecular weight distribution (M
w
/M
n
) no greater than about 3.5 and (b) from about 70 to about 30 weight percent of a propylene based polymer. U.S. Pat. No. 5,358,792 is incorporated herein by reference in its entirety.
U.S. Pat. No. 6,231,975, issued May 15, 2001, discloses an oriented sealable film comprising: (a) a core layer comprising an olefin polymer which comprises polypropylene, high density polyethylene or ethylene-propylene copolymer or terpolymer, wherein the polypropylene comprises greater than about 80 wt % of isotactic polypropylene or greater than about 80 wt % of syndiotactic polypropylene, wherein the percentages are based on the entire weight of the polypropylene of the core layer; (b) a sealing layer selected from the group consisting of ethylene-propylene random copolymer, ethylene-butene-1 copolymer, ethylene-propylene-butene-1 terpolymer, propylene-butene copolymer, low density polyethylene, linear low density polyethylene, very low density polyethylene, metallocene catalyzed polyethylene plastomer, metallocene catalyzed polyethylene, metallocene catalyzed ethylene-hexene copolymer, metallocene catalyzed ethylene-butene copolymer, metallocene catalyzed ethylene-octene copolymer, ethylene-methacrylate copolymer, ethylene-vinyl acetate copolymer and ionomer resin; and (c) a separable layer positioned between the core layer and the sealing layer, the separable layer comprising a blend of linear low density polyethylene and ethylene-propylene block copolymer.
SUMMARY OF THE INVENTION
This invention relates to a sealable film comprising:
(a) a core layer comprising an olefin polymer wherein the core layer comprises the interior of the film;
(b) a separable layer exterior to the core layer, wherein the separable layer comprises (1) an impact copolymer layer; (2) a thermoplastic polyolefin (TPO) layer; (3) a blend of impact copolymer and LLDPE; or (4) a blend of two or more incompatible polymers;
(c) an optic improving layer exterior to the core layer and the separable layer, wherein the optic improving layer comprises a polymer having an optic improving level of modulus, hardness, and/or beam strength; and
(d) a sealing layer exterior to the core layer, the separable layer, and the optic improving layer, wherein the sealing layer comprises a polymer.
Objects and advantages of the invention include one or more of the following:
To provide a thermoplastic film having at least four layers, including a seal layer, which is sealable to itself and other surfaces, but which permits separation of the seal layer from at least one other layer of the film.
To provide a thermoplastic film having one or more separable layers positioned to permit separation of the sealing layer from at least one other layer of the film.
To provide a multilayer film comprising a core layer and a sealing layer, so that when sealed to itself, or another surface, the sealing layer can be separated from the other layers of the film.
To provide a thermoplastic film suited for packaging applications.


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patent: WO9604178 (1996-02-01), None
patent: WO 98/32596 (1998-07-01), None

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