Stock material or miscellaneous articles – Structurally defined web or sheet – Including components having same physical characteristic in...
Reexamination Certificate
2001-02-27
2002-11-12
Nakarani, D. S. (Department: 1773)
Stock material or miscellaneous articles
Structurally defined web or sheet
Including components having same physical characteristic in...
C428S215000, C428S216000, C428S516000, C428S517000, C428S519000, C428S520000, C428S910000
Reexamination Certificate
active
06479138
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to an oriented, heat shrinkable thermoplastic film.
BACKGROUND OF THE INVENTION
“Soft shrink” films are known in the art. These films offer relatively high free shrink combined with relatively low shrink tension. They are suitable for packaging articles, such as textiles and paper, that are sensitive to, or whose packaged appearance suffers from effects, such as distortion, of a film with too high a shrink tension.
An example of such films is poly(vinyl chloride) (hereinafter “PVC”) film. PVC film exhibits good elastic recovery, high modulus, and low shrink tension. Unfortunately, PVC film suffers from poor sealability, low free shrink, and poor tear resistance. It also carbonizes during a heat sealing process, releasing hydrogen chloride. The ensuing hydrochloric acid attacks and corrodes metal surfaces of equipment.
Polyolefinic packaging materials have been developed for soft shrink end-use. An example is the polyolefinic film supplied commercially by Cryovac, Inc. under the designation D-940™. This film provides a commercially useful alternative to PVC film, without the disadvantages of a chlorine-containing material. However, it would be desirable to provide a chlorine-free film that avoids the disadvantages of PVC film, but offers higher modulus and better elastic recovery than that now available from D-940, while maintaining good heat seal quality, high free shrink and a low shrink tension. Additionally, it would be advantageous to provide such attributes in a chlorine-free film having better optical quality (low haze) than is found in several present low shrink force chlorine-free films.
SUMMARY OF THE INVENTION
In a first aspect, a multilayer solid state oriented heat shrinkable film comprises a core layer comprising a linear random alpha-olefin/vinyl aromatic copolymer; and a first and second outer layer each comprising an olefinic polymer; wherein the film has a Young's modulus of between 50,000 and 200,000 pounds per square inch in at least one of the longitudinal and transverse directions; a free shrink of between 40% and 80% at 240° F. in at least one of the longitudinal and transverse directions; a shrink tension of between 50 and 400 pounds per square inch, or a shrink force of between 20 and 180 grams, at 240° F. in at least one of the longitudinal and transverse directions; and a haze of less than 6.
In a second aspect, a multilayer solid state oriented heat shrinkable film comprises a core layer comprising a linear random alpha-olefin/vinyl aromatic copolymer; a first and second intermediate layer each comprising an ethylene copolymer having a melt index less than 2.0; and a first and second outer layer each comprising an olefinic polymer; wherein the film has a Young's modulus of between 50,000 and 200,000 pounds per square inch in at least one of the longitudinal and transverse directions; a free shrink of between 40% and 80% at 240° F. in at least one of the longitudinal and transverse directions; a shrink tension of between 50 and 400 pounds per square inch, or a shrink force of between 20 and 180 grams, at 240° F. in at least one of the longitudinal and transverse directions; and a haze of less than 6.
In a third aspect, a multilayer oriented heat shrinkable film comprises a core layer comprising an ethylene copolymer having a melt index less than 2.0; a first and second intermediate layer each comprising a linear random alpha-olefin/vinyl aromatic copolymer; and a first and second outer layer each comprising an olefinic polymer; wherein the film has a Young's modulus of between 50,000 and 200,000 pounds per square inch in at least one of the longitudinal and transverse directions; a free shrink of between 40% and 80% at 240° F. in at least one of the longitudinal direction and transverse direction; a shrink tension of between 50 and 400 pounds per square inch, or a shrink force of between 20 and 180 grams, at 240° F. in at least one of the longitudinal and transverse directions; and a haze of less than 6.
In a fourth aspect, a method of making a film comprises extruding a sheet of film comprising a core layer comprising a linear random alpha-olefin/vinyl aromatic copolymer; and a first and second outer layer each comprising an olefinic polymer; quenching the extruded sheet of film; reheating the quenched sheet of film to its orientation temperature; and orienting the reheated sheet of film to produce a heat shrinkable film, the film having a Young's modulus of between 50,000 and 200,000 pounds per square inch in at least one of the longitudinal and transverse directions; a free shrink of between 40% and 80% at 240° F. in at least one of the longitudinal and transverse directions; a shrink tension of between 50 and 400 pounds per square, inch, or a shrink force of between 20 and 180 grams, at 240° F. in at least one of the longitudinal and transverse directions; and a haze of less than 6.
In a fifth aspect, a method of making a film comprises extruding a sheet of film comprising a core layer comprising a linear random alpha-olefin/vinyl aromatic copolymer; a first and second intermediate layer each comprising an ethylene copolymer having a melt index less than 2.0; and a first and second outer layer each comprising an olefinic polymer; quenching the extruded sheet of film; reheating the quenched sheet of film to its orientation temperature; and orienting the reheated sheet of film to produce a heat shrinkable film, the film having a Young's modulus of between 50,000 and 200,000 pounds per square inch in at least one of the longitudinal and transverse directions; a free shrink of between 40% and 80% at 240° F. in at least one of the longitudinal and transverse directions; a shrink tension of between 50 and 400 pounds per square inch, or a shrink force of between 20 and 180 grams, at 240° F. in at least one of the longitudinal and transverse directions; and a haze of less than 6.
In a sixth aspect, a method of making a film comprising extruding a sheet of film comprising a core layer comprising an ethylene copolymer having a melt index less than 2.0; a first and second intermediate layer each comprising a linear random alpha-olefin/vinyl aromatic copolymer; and a first and second outer layer each comprising an olefinic polymer; quenching the extruded sheet of film; reheating the quenched sheet of film to its orientation temperature; and orienting the reheated sheet of film to produce a heat shrinkable film, the film having a Young's modulus of between 50,000 and 200,000 pounds per square inch in at least one of the longitudinal and transverse directions; a free shrink of between 40% and 80% at 240° F. in at least one of the longitudinal and transverse directions; a shrink tension of between 50 and 400 pounds per square inch, or a shrink force of between 20 and 180 grams, at 240° F. in at least one of the longitudinal and transverse directions; and a haze of less than 6.
In any of the above-disclosed methods, the quenched extruded sheet of film can optionally be irradiated before the reheating step.
The reheated sheet of film can be oriented by e.g. trapped bubble orientation or tenter frame orientation.
Definitions
“Alpha-olefin” herein refers to olefinic compounds, whether unsubstituted or substituted, in which the first two carbon atoms in the chain have a double bond therebetween. Examples include ethylene, propylene, hexene, and octene.
“Alpha-olefin/vinyl aromatic copolymer” (AO/VA) herein refers to homogeneous copolymers made from an alpha-olefinic monomer having from two to eight carbon atoms per molecule, and a vinyl aromatic monomer. An example is ethylene/styrene copolymer. The alpha-olefin/vinyl aromatic copolymer herein is a random linear copolymer and includes a pseudo-random copolymer. Although the present description primarily focuses on olefin/vinyl aromatic copolymers, terpolymers are also within the scope of such term. Terpolymers include ethylene/octene/styrene, ethylene/styrene/butene, propylene/styrene/ethylene, and ethylene/styrene/hexene terpolymers.
Cryovac Inc.
Nakarani D. S.
Quatt Mark B.
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