Stock material or miscellaneous articles – Composite – Of addition polymer from unsaturated monomers
Reexamination Certificate
2000-09-29
2002-11-12
Tarazano, D. Lawrence (Department: 1773)
Stock material or miscellaneous articles
Composite
Of addition polymer from unsaturated monomers
C428S522000, C428S910000, C525S239000
Reexamination Certificate
active
06479162
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a vinylidene chloride polymer composition, and films made from the composition, including films suitable for the packaging of food products, such as meat.
BACKGROUND OF THE INVENTION
Thermoplastic packaging films made of vinylidene chloride polymer (herein referred to as “PVdC”), have been used for the packaging of food products such as fresh and processed meats and other items.
Multilayer, oriented, heat-shrinkable films including at least one layer containing PVdC have been produced by extrusion, coextrusion, lamination, and extrusion coating.
Chinese sausage is currently packaged in films such as monolayer films made up of a DOW 2032™ PVdC and formulated with plasticizers, heat stabilizers, antioxidants, UV absorbers, pigments, slip agents, antiblock agents, etc. Although this film offers good package color and thermal stability during extrusion of the packaging film, it exhibits a marginally stable trapped bubble, and a very narrow processing window, during orientation. As a result, manufacture of the film becomes a very difficult process in which bubble instability during orientation can easily occur. This can and does result in downtime from failure of the trapped bubble, or in processing speeds that are slower (and hence more expensive) than desirable to avoid such bubble failure.
An alternative PVdC copolymer, POVIDEN™ Type 2 PVdC having a weight average molecular weight of 130,000, and available from Kaustic of Volgograd, Russia, was tested by the applicant by extruding this material into a monolayer film and orienting the film. This was an effort to identify and provide a material which helps provide a more stable bubble process. However, it was found that although a more stable bubble process was obtained, this was at the expense of greater thermal instability during extrusion, leading to a film with too dark a color.
The applicant has now discovered that the composition disclosed herein, provides a combination of good thermal stability, color appearance, extrudability, orientability, Young's modulus, package firmness, and free shrink ratio properties in films of the invention, that is unavailable from either the DOW 2032 vinylidene chloride polymer alone, or the POVIDEN vinylidene chloride polymer alone.
SUMMARY OF THE INVENTION
A composition comprises greater than 50% by weight of a first vinylidene chloride polymer having a weight average molecular weight of between 80,000 and 125,000, and less than 50% by weight of a second vinylidene chloride polymer having a weight average molecular weight of between 126,000 and 180,000, the weight percent of each of the first and second polymers based on the combined weight of the first and second polymers.
A composition comprises between 51% and 99% by weight of a first vinylidene chloride polymer having a weight average molecular weight of between 80,000 and 125,000, and between 1% and 49% by weight of a second vinylidene chloride polymer having a weight average molecular weight of between 126,000 and 180,000, the weight percent of each of the first and second polymers based on the combined weight of the first and second polymers.
A film comprises at least one layer comprising a composition having greater than 50% by weight of a first vinylidene chloride polymer having a weight average molecular weight of between 80,000 and 125,000, and less than 50% by weight of a second vinylidene chloride polymer having a weight average molecular weight of between 126,000 and 180,000, the weight percent of each of the first and second polymers based on the combined weight of the first and second polymers.
A film comprises at least one layer comprising a composition having between 51% and 99% by weight of a first vinylidene chloride polymer having a weight average molecular weight of between 80,000 and 125,000, and between 1% and 49% by weight of a second vinylidene chloride polymer having a weight average molecular weight of between 126,000 and 180,000, the weight percent of each of the first and second polymers based on the combined weight of the first and second polymers.
A biaxially oriented film comprises at least one layer comprising a blend of a first vinylidene chloride polymer and a second vinylidene chloride polymer, the film having a free shrink ratio of between 0.6 and 2.2 at a shrink temperature of 180° F.
A biaxially oriented film comprises at least one layer comprising a blend of a first vinylidene chloride polymer and a second vinylidene chloride polymer, the film having a free shrink ratio of between 0.8 and 1.4 at a shrink temperature of 200° F.
Definitions
“vinylidene chloride polymer” and “PVdC” herein refer to a vinylidene chloride-containing polymer or copolymer, i.e., a polymer that includes monomer units derived from vinylidene chloride (CH
2
=CCl
2
) and also, optionally, monomer units derived from one or more of vinyl chloride, styrene, vinyl acetate, acrylonitrile, and C
1
-C
12
alkyl esters of (meth)acrylic acid (e.g., methyl acrylate, butyl acrylate, methyl methacrylate, etc.). Thus, “vinylidene chloride polymer” and “PVdC” include one or more of vinylidene chloride homopolymer, vinylidene chloride/vinyl chloride copolymer, vinylidene chloride/methyl acrylate copolymer, vinylidene chloride/acrylonitrile copolymer, vinylidene chloride/butyl acrylate copolymer, vinylidene chloride/styrene copolymer, and vinylidene chloride/vinyl acetate copolymer. The weight percent of the vinylidene chloride monomer can be between 75% and 95% by weight of the copolymer; the weight percent of the second monomer, e.g. vinyl chloride, can be between 5% and 25% by weight of the copolymer;
“(meth)acrylic acid” herein refers to both acrylic acid and/or methacrylic acid;
“(meth)acrylate” herein refers to both acrylate and methacrylate;
“polymer” herein refers to the product of a polymerization reaction, and is inclusive of homopolymers, copolymers, terpolymers, tetrapolymers, etc.;
“copolymer” herein refers to a polymer formed by the polymerization reaction of at least two different monomers and is inclusive of random copolymers, block copolymers, graft copolymers, etc.;
“ethylene/alpha-olefin copolymer” (EAO) herein refers to copolymers of ethylene with one or more comonomers selected from C
3
to C
10
alpha-olefins such as propene, butene-1, hexene-1, octene-1, etc. in which the molecules of the copolymers comprise long polymer chains with relatively few side chain branches arising from the alpha-olefin which was reacted with ethylene. This molecular structure is to be contrasted with conventional high pressure low or medium density polyethylenes which are highly branched with respect to EAOs and which high pressure polyethylenes contain both long chain and short chain branches. EAO includes 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), such as DOWLEX™ or ATTANE™ resins supplied by Dow, ESCORENE™ or EXCEED™ resins supplied by Exxon; as well as linear homogeneous ethylene/alpha olefin copolymers (HEAO) such as TAFMER™ resins supplied by Mitsui Petrochemical Corporation, EXACT™ resins supplied by Exxon, or long chain branched (HEAO) AFFINITY™ resins supplied by the Dow Chemical Company, or ENGAGE™ resins supplied by DuPont Dow Elastomers;
“package” herein refers to a film configured around a product;
“film” herein refers to plastic web materials having a thickness of 0.50 mm (20 mils) or less such as 0.25 mm (10 mils) or less;
“inner layer” herein refers to any layer of a multilayer film having both of its principal surfaces directly adhered to another layer of the film;
“outer layer” herein refers to any layer of a film having only one of its principal surfaces directly adhered to another layer of the film;
“seal layer” herein refers to a layer of a film that can be involved in the sealing of the film to itself or another layer;
“seal” herein refers to a bonding of a first film surface to a second film surface created by heating
Cryovac Inc.
Quatt Mark B.
Tarazano D. Lawrence
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