Stock material or miscellaneous articles – Hollow or container type article – Nonself-supporting tubular film or bag
Reexamination Certificate
2002-03-25
2004-05-18
Nakarani, D. S. (Department: 1773)
Stock material or miscellaneous articles
Hollow or container type article
Nonself-supporting tubular film or bag
C156S292000, C156S308400, C264S173190, C428S035700, C428S220000, C428S516000, C428S517000, C428S906000, C428S910000
Reexamination Certificate
active
06737130
ABSTRACT:
FIELD OF THE INVENTION
The present invention pertains to packaging articles, particularly articles having a hermetic heat seal, as well as to reclosable packaging articles.
BACKGROUND OF THE INVENTION
Various means have been utilized to provide reclosable packaging which protects the contents against dehydration or leakage once the package is opened. Typical means have included interlocking closure strips, “zippers”, fasteners, ties, and uncovered pressure-sensitive adhesive strips, positioned on a heat sealed package. These reclosure means all require additional steps in the manufacture of the package, in that the reclosing means must in some way be incorporated onto the package, e.g., adhered, tied around, or sealed to the other components as a means of becoming another component of the package. Other means have included a heat sealable multilayer film containing a layer other than the heat seal layer consisting of a polymer having enough “cold tack” to provide the property of self-adhesion or adhesion to other materials for the purpose of reclosing a package. However, such adhesive materials have been difficult to process due to the presence of low molecular weight tackifing agents and/or have had organoleptic problems and food law problems associated therewith. It would be desirable to provide a coextruded multilayer film, comprising a single film layer capable of forming a hermetic heat seals while at the same time having reclosable properties without the additional processing steps associated with attaching a separate closure device, and without the organoleptic problems of prior art approaches.
SUMMARY OF THE INVENTION
It has been discovered that a particular new type of highly branched polyolefin, herein referred to as a “substantially spherical homogeneous polyolefin”, has the ability to provide a film seal layer with the dual properties of being hermetically heat sealable and pressure-reclosable, thereby making it unnecessary to affix a separate re-closure device such as a zipper or other closure device. The hermetic seal is fused so that it is impervious to air and liquid, such as water. The SSH polyolefin may be coextruded in the seal layer in the production of a monolayer or multilayer film. The substantially spherical polyolefin does not require the addition of low molecular weight tackifier to accomplish the dual function, and therefore does not exhibit many of the processing and organoleptic problems associated with high cold tack polymer formulations of the prior art.
As a first aspect, the present invention is directed to a multilayer film comprising a hermetically heat-sealable, pressure-reclosable, outer heat seal layer which comprises a blend of a substantially spherical homogeneous polyolefin with a different thermoplastic polymer. Preferably, the outer heat seal layer and one other layer of the multiplayer film are coextruded. Preferably, all layers of the multiplayer film are coextruded. The substantially spherical polyolefin is present in an amount of from about 20 to 80 weight percent, based on total weight of the heat seal layer. The different thermoplastic polymer is present in the layer in an amount of from about 80 to 20 weight percent, based on total layer weight. The substantially spherical polyolefin has at least 60 side chain branches per 1000 carbon atoms, and contains for every 100 branches that are methyl, 1 to about 80 ethyl branches, 1 to about 20 propyl branches, 1 to about 50 butyl branches, 1 to about 20 amyl branches, and 1 to about 100 hexyl or longer branches. The substantially spherical homogeneous polyolefin has a melt index of from about 1 to 10.
More preferably, the substantially spherical homogeneous polyolefin has from about 65 to about 140 branches per 1000 methylene groups, and for every 100 branches that are methyl, about 1 to about 20 ethyl branches, 1 to about 10 propyl branches, 1 to about 15 butyl branches, 1 to about 10 amyl branches, and 1 to about 35 hexyl or longer branches. More preferably, the substantially spherical homogeneous polyolefin has at least 70 branches per 1000 carbon atoms. More preferably, the substantially spherical homogeneous polyolefin has from about 80 to about 125 branches per 1000 methylene groups, and contains for every 100 branches that are methyl, about 2 to about 18 ethyl branches, about 2 to about 8 propyl branches, about 2 to about 12 butyl branches, about 2 to about 8 amyl branches, and about 8 to about 30 hexyl or longer branches. More preferably, the substantially spherical homogeneous polyolefin has from about 85 to about 120 branches per 1000 methylene groups. More preferably, the substantially spherical homogeneous polyolefin has from about 75 to about 85 branches per 1000 methylene groups.
Preferably, the substantially spherical homogeneous polyolefin has a density of from about 0.85 to 0.88 g/cm
3
. Preferably, the substantially spherical homogeneous polyolefin is present in the outer layer in an amount of at least 30 to 70 weight percent.
Preferably, the substantially spherical homogeneous polyolefin is a homopolymer derived from ethylene. Preferably, the substantially spherical homogeneous polyolefin is a copolymer comprising mer units derived from ethylene and one or more members selected from the group consisting of propylene, butene, hexene, and octene.
Preferably, the different polymer comprises at least one member selected from the group consisting of polyolefin homopolymer, ethylene/alpha-olefin copolymer, polyamide, polyester, ethylene/vinyl alcohol copolymer, halogenated polymer, polystyrene, polynorbornene, ethylene/ester copolymer, and ethylene/unsaturated acid polymer.
Optionally, the film is heat-shrinkable.
Preferably, the film has a thickness of from about 0.3 to 25 mils.
Preferably, the film is capable of exhibiting a strength of a 40 psi pressure-induced bond of at least 100 grams per centimeter for at least 2 repetitions.
Preferably, the multilayer film is produced using a coextrusion process. Alternatively, the film is produced using a lamination process.
In one preferred embodiment, the multilayer film further comprises an oxygen barrier layer.
As a second aspect, the invention is directed to a process for making a multilayer film. The process comprises (A) coextruding a first layer and a second layer, wherein the first layer is an outer film layer in accordance with the heat seal layer according to the first aspect of the present invention, and (B) orienting the extrudate so that an oriented film is formed.
As a third aspect, the invention is directed to a roll of film comprising a disposable outer layer which is directly and peelably adhered to a first surface of second layer which is compositionally in accordance with the seal layer according to the first aspect of the present invention. The second layer is hermetically heat-sealable, and pressure-reclosable, and a second surface of the second layer is directly adhered to a thermoplastic third layer.
As a fourth aspect, the present invention is directed to a packaging article comprising an inside layer in accordance with the seal layer according to the first aspect of the present invention. The inside layer is heat sealed to itself or another component of the article, with the inside layer being hermetically heat-sealable and pressure-reclosable to itself or the other component. Preferably, the packaging article is a bag and the inside layer is hermetically heat sealed to itself. Preferably, the multilayer film is heat sealed to a second component which is molded or thermoformed.
As a fifth aspect, the present invention is directed to a process for making a sealed article, comprising: (A) providing a film having a seal layer in accordance with the first aspect of the present invention, and (B) heat sealing the film to itself or another article by heating the seal layer to a temperature of at least 50° C.
As a sixth aspect, the present invention is directed to a hermetically heat sealable, pressure-reclosable multilayer film comprising: (A) a sealant layer comprising, at least 30% by weight of a single sit
Cryovac Inc.
Hurley Jr. Rupert B.
Nakarani D. S.
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