Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – At least one aryl ring which is part of a fused or bridged...
Reexamination Certificate
2000-05-19
2003-02-25
Mullis, Jeffrey (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
At least one aryl ring which is part of a fused or bridged...
C524S401000, C524S403000, C524S413000, C524S435000, C525S047000
Reexamination Certificate
active
06525123
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to the field of oxygen scavenging polymers. More particularly, it concerns blends of ethylene/vinyl alcohol copolymers (EVOH) with oxygen scavenging polymers, methods of making the blends, packaging articles comprising the blends, and methods of making the packaging articles.
2. Description of Related Art
It is well known that limiting the exposure of oxygen-sensitive products to oxygen maintains and enhances the quality and shelf-life of the product. For instance, by limiting the oxygen exposure of oxygen sensitive food products in a packaging system, the quality of the food product is maintained, and food spoilage is avoided. In addition such packaging also keeps the product in inventory longer, thereby reducing costs incurred from waste and restocking. In the food packaging industry, several means for limiting oxygen exposure have already been developed, including modified atmosphere packaging (MAP), vacuum packaging and oxygen barrier film packaging. In the first two instances, reduced oxygen environments are employed in the packaging, while in the latter instance, oxygen is physically prevented from entering the packaging environment.
Another, more recent, technique for limiting oxygen exposure involves incorporating an oxygen scavenger into the packaging structure. Incorporation of a scavenger in the package can scavenge environmental oxygen as it diffuses into the packaging structure, as well as scavenging residual oxygen present inside the package upon filling. Generally, the oxygen scavenger functions by irreversibly reacting with oxygen, and as a result, there exists a maximum amount of oxygen (the “oxygen scavenging capacity”) that the scavenger can scavenge. However, increasing the oxygen scavenging capacity by increasing the quantity of the oxygen scavenging polymer has the disadvantage of, typically, impairing the structural properties of the packaging article, as well as increasing the cost of materials and the cost or complexity of processing.
From this, it will be recognized that limiting oxygen ingress into the packaging article is beneficial. If oxygen ingress into the packaging article is limited, less of the oxygen scavenging polymer will be required, and less can be used, thus improving the physical properties and processing of the packaging article. This is especially significant for products that are oxygen-sensitive but otherwise fairly resistant to spoilage, and are thus capable of shelf-lives on the order of at least months, or up to a year or more, such as beer or wine.
Ethylene/vinyl alcohol copolymer (EVOH) is widely known for having excellent barrier properties to gases (such as O
2
and CO
2
) and other fluids, and has found wide use in packaging applications where barrier properties are desired. However, it is generally regarded as an insufficient oxygen barrier for packaging applications which require very strong oxygen barrier properties over a long period of time, such as beer packaging.
Therefore, it would be desirable to have a packaging article comprising EVOH and an additional component or components, which packaging article would be better suited for providing a very strong oxygen barrier over a long period of time than are packaging articles currently known.
Beer in PET, Part I of III (Packaging Strategies, Inc., eds., West Chester, Pa.) (1999), reports the reputed testing of a blend of an oxygen scavenger and an ethylene/vinyl alcohol copolymer (EVOH) in a packaging article for packaging beer. The identity of the oxygen scavenger, and the proportions of the oxygen scavenger and EVOH in the blend, were not reported.
SUMMARY OF THE INVENTION
In one set of embodiments, the present invention relates to a composition, comprising a blend of an ethylene/vinyl alcohol copolymer (EVOH) and an oxygen scavenging polymer. In one embodiment, the composition can be in the form of a cross-linked blend, and can further comprise a compatibilizer or a catalyst. Preferably, if the blend is cross-linked, it is cross-linked by transesterification.
In a related embodiment, the present invention also relates to a packaging article comprising at least one layer comprising the blend of EVOH and an oxygen scavenging polymer. The packaging article can be a single-layer or a multilayer article, and can be flexible or rigid. A multilayer packaging article can further comprise a structural layer or layers, an oxygen barrier layer, an oxygen scavenging layer, an oxygen permeable layer or layers, or an adhesive layer or layers, among others.
In yet another embodiment, the present invention relates to a method of making the blend of EVOH and an oxygen scavenging polymer, comprising providing EVOH and the oxygen scavenging polymer, and blending the materials. The blending step can further comprise cross-linking of the materials, such as by transesterification.
The present invention provides packaging articles that have a very strong oxygen barrier for a long period of time, by taking advantage of the inherent oxygen barrier property of EVOH and the oxygen scavenging property of the oxygen scavenging polymer. The present invention also provides packaging articles having the advantages of providing a CO
2
barrier (useful in retaining the carbonation of packaged soft drinks, beer, and sparkling wines) and comprising a blend of EVOH and the oxygen scavenging polymer which has good clarity and is readily processible into a variety of formulations.
DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS
Oxygen barrier compositions
In one embodiment, the present invention relates to a composition, comprising a blend of an ethylene/vinyl alcohol copolymer (EVOH) and an oxygen scavenging polymer. Such a composition is useful as a component of a high oxygen barrier layer of a packaging article. By “high oxygen barrier layer” is meant a layer comprising the blend of EVOH and the oxygen scavenging polymer.
Packaging articles typically come in several forms including a single layer film, a multilayer film, a single layer rigid article, or a multilayer rigid article. Typical rigid or semirigid articles include plastic, paper or cardboard cartons or bottles such as juice containers, soft drink containers, thermoformed trays, or cups, which have wall thicknesses in the range of 100 to 1000 micrometers. Typical flexible bags include those used to package many food items, and will likely have thicknesses of 5 to 250 micrometers. The walls of such articles either comprise single or multiple layers of material.
The packaging article comprising the oxygen barrier composition can be used to package any product for which it is desirable to inhibit oxygen damage during storage, e.g. food, beverage, pharmaceuticals, medical products, corrodible metals, or electronic devices. It is especially useful for packaging products for which it is desirable to maintain a high oxygen barrier for a long period of time, e.g. beer, wine, and other beverages. It is also especially useful for packaging products for which it is desirable to retain carbon dioxide, e.g. beer, sparkling wine, and soft drinks.
The packaging article comprising the oxygen barrier composition can comprise a single layer comprising the composition, or a high oxygen barrier layer and additional layers, such as an oxygen scavenging layer, a conventional oxygen barrier layer (e.g. comprising EVOH or another known barrier compound, but not comprising an oxygen scavenging polymer), a food-contact layer, a structural layer, or an adhesive layer, alone or in any combination. Single layered packaging articles can be prepared by solvent casting, injection molding, blow molding, or by extrusion, among other techniques. Packaging articles with multiple layers are typically prepared using coextrusion, injection molding, blow molding, coating, or lamination, among other techniques.
The packaging article can comprise any oxygen barrier composition described below.
As stated above, the oxygen barrier composition comprises a blend of an ethylene/vinyl alcohol copolymer (E
Cai Gangfeng
Ching Ta Yen
Yang Hu
Chevron Phillips Chemical Company LP
Mullis Jeffrey
Williams Morgan & Amerson P.C.
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