Stock material or miscellaneous articles – Composite – Of addition polymer from unsaturated monomers
Reexamination Certificate
1999-03-05
2001-10-02
Acquah, Samuel A. (Department: 1711)
Stock material or miscellaneous articles
Composite
Of addition polymer from unsaturated monomers
C428S034900, C428S035100, C428S213000, C428S218000, C428S220000, C428S332000, C428S516000, C428S522000, C428S910000, C525S220000, C525S221000, C525S240000, C264S290200
Reexamination Certificate
active
06296947
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a high stiffness (high modulus) thermoplastic film which may be utilized to package a wide variety of items.
BACKGROUND OF THE INVENTION
The present invention is directed to a new and useful film. Films, and especially heat shrinkable films are well known for many packaging applications. An example is D-955 film supplied commercially by W. R. Grace. This film has proven to be very useful in packaging applications where high shrink, good optics, and other desirable features of the packaging film are needed. These additional features include impact resistance, tear initiation and tear propagation resistance. Films of this type are disclosed in U.S. Pat. Nos. 4,551, 380 and 4, 643,943, both to Schoenberg, incorporated herein by reference in their entirety.
It would be desirable to use heat shrinkable materials like D-955 in end use applications requiring relatively high stiffness, i.e. high modulus. One example of such an end use is on certain high speed packaging machines. Unfortunately, these films do not have sufficient stiffness to provide an optimal packaging material for such uses.
It would also be desirable to provide a material that has a reduced thickness compared to many commercial films. This would offer reduced costs in manufacture, because of the reduction in the amount of raw material used to make the film. It would also offer an environmentally attractive film because of source reduction. However, in attempting to achieve this by simply downgauging currently available films, degradation of film properties can occur. These properties include modulus (stiffness), which as already pointed out is already marginal or unacceptably low for some packaging applications; heat seal strength, and impact resistance.
It would in addition be desirable to provide a material that has a reduced shrink force compared to many commercial films. This would offer utility in packaging applications where the product to be packaged is sensitive to high shrink forces, and can be distorted by such films when heat shrunk around the product.
SUMMARY OF THE INVENTION
In one aspect, the film of the present invention comprises a layer comprising a blend of an ethylene polymer having a density of at least 0.925 grams per cubic centimeter, and an ethylene copolymer selected from the group consisting of ethylene/ester copolymer, and ethylene/alpha-olefin copolymer, said layer substantially free from linear low density polyethylene.
In a second aspect, a multilayer film comprises a core layer comprising an ethylene polymer having a density of at least 0.925 grams per cubic centimeter; and two outer layers each comprising a blend of an ethylene polymer having a density of at least 0.925 grams per cubic centimeter, and an ethylene copolymer selected from the group consisting of ethylene/ester copolymer, and ethylene/alpha-olefin copolymer, at least one of said outer layers substantially free from linear low density polyethylene.
In a third aspect, a multilayer film comprises a core layer comprising an ethylene polymer having a density of at least 0.925 grams per cubic centimeter; at least one intermediate layer comprising an ethylene copolymer having a density of less than 0.925 grams per cubic centimeter; and two outer layers each comprising a blend of an ethylene polymer having a density of at least 0.925 grams per cubic centimeter, and an ethylene copolymer selected from the group consisting of ethylene/ester copolymer, and ethylene/alpha-olefin copolymer, at least one of said outer layers substantially free from linear low density polyethylene.
In a fourth aspect, a film comprises a layer comprising a blend of an ethylene polymer having a density of at least 0.925 grams per cubic centimeter, and an ethylene copolymer selected from the group consisting of ethylene/ester copolymer, and ethylene/alpha-olefin copolymer, said film having a thickness of less than 0.50 mils.
In a fifth aspect, a film consisting essentially of a layer comprising a blend of an ethylene polymer having a density of at least. 0.925 grams per cubic centimeter, and an ethylene copolymer selected from the group consisting of ethylene/ester copolymer, and ethylene/alpha-olefin copolymer, said film having a thickness of less than 0.60 mils.
In a sixth aspect, a film comprises a layer comprising a blend of an ethylene polymer having a density of at least 0.925 grams per cubic centimeter, and an ethylene copolymer selected from the group consisting of ethylene/ester copolymer, and ethylene/alpha-olefin copolymer, said film having a shrink force of less than 0.35 pounds in the longitudinal direction, and less than 0.30 pounds in the transverse direction.
In a seventh aspect, a multilayer film comprises a core layer comprising an ethylene polymer having a density of at least 0.925 grams per cubic centimeter; and two outer layers each comprising a blend of an ethylene polymer having a density of at least 0.925 grams per cubic centimeter, and an ethylene copolymer selected from the group consisting of ethylene/ester copolymer, and ethylene/alpha-olefin copolymer, said film having a modulus of at least 60,000 psi in the longitudinal direction, and at least 75,000 psi in the transverse direction.
In an eighth aspect, a film comprises a layer comprising a blend of between 26% and 69% of an ethylene polymer having a density of at least 0.925 gm/cc, and between 31% and 74% of an ethylene copolymer selected from the group consisting of ethylene/ester copolymer and ethylene/alpha-olefin copolymer.
DEFINITIONS
The term “core layer” as used herein refers to the central layer of a multi-layer film.
The term “outer layer” as used herein refers to what is typically an outermost, usually surface layer of a multi-layer film, although additional layers and/or films can be adhered to it.
“Polymer” herein includes homopolymer, copolymer, terpolymer, etc. “Copolymer” herein includes copolymer, terpolymer, etc.
All compositional percentages used herein are calculated on a “by weight” basis.
The term “intermediate” as used herein refers to a layer of a multi-layer film which is between an outer layer and core layer of the film.
“Linear low density polyethylene” (LLDPE) as used herein has a density in the range of from about 0.916 to 0.924 grams per cubic centimeter. “Linear medium density polyethylene” (LMDPE) as used herein, has a density from 0.930 grams per cubic centimeter to 0.939 grams per cubic centimeter. “High density polyethylene” (HDPE), as defined herein, has a density of 0.94 grams per cubic centimeter or more.
The term “ethylene/ester copolymer” (E/E) as used herein refers to a copolymer formed from ethylene and an ester such as vinyl acetate, alkyl acrylate, or other monomers, wherein the ethylene derived units in the copolymer are present in major amounts and the ester derived units in the copolymer are present in minor amounts.
As used herein, the phrase “ethylene/alpha-olefin copolymer” (EAO) refers to such heterogeneous materials as linear medium density polyethylene (LMDPE), linear low density polyethylene (LLDPE), and very low and ultra low density polyethylene (VLDPE and ULDPE); as well as homogeneous polymers (HEAO) such as TAFMER (TM) ethylene/alpha olefin copolymers supplied by Mitsui Petrochemical Corporation and metallocene-catalyzed polymers such as EXACT (TM) materials supplied by Exxon. These materials generally include copolymers of ethylene with one or more comonomers selected from C
4
to C
10
alpha-olefins such as butene-1 (i.e., 1-butene), hexene-1, octene-1, etc. in which the molecules of the copolymers comprise long chains with relatively few side chain branches or cross-linked structures. This molecular structure is to be contrasted with conventional low or medium density polyethylenes which are more highly branched than their respective counterparts. Other ethylene/alpha-olefin copolymers, such as the long chain branched homogeneous ethylene/alpha-olefin copolymers available from the Dow Chemical Company, known as AFFINITY (TM) resins, are also included as anothe
Acquah Samuel A.
Cryovac Inc.
Quatt Mark B.
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