Stock material or miscellaneous articles – Hollow or container type article – Nonself-supporting tubular film or bag
Reexamination Certificate
2001-02-07
2004-01-27
Pyon, Harold (Department: 1772)
Stock material or miscellaneous articles
Hollow or container type article
Nonself-supporting tubular film or bag
C428S035800, C428S035900, C428S215000, C428S219000, C428S323000, C428S349000, C428S516000, C252S188280, C252S181300, C252S383000, C526S308000, C526S348000
Reexamination Certificate
active
06682791
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to articles and methods for scavenge oxygen in packages containing oxygen-sensitive products, in particular food and beverage products.
BACKGROUND OF THE INVENTION
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. By limiting the oxygen exposure of oxygen sensitive products in a packaging system, the quality of the product is maintained and spoilage or damage due to oxygen contamination is avoided. In addition such packaging also keeps the product in inventory longer, thereby reducing costs incurred from waste and having to restock.
There are two main sources of oxygen contamination in a package: the head space oxygen and ingress oxygen. The head space oxygen is the oxygen remaining in the package after the product has been sealed off within packaging materials. Ingress oxygen is the oxygen which diffuses directly through the package walls or enters the package through voids or holes in the package (particularly at the seals). Contamination by head space oxygen occurs only when the package is initially sealed. By contrast, the ingress oxygen enters the package slowly from the time the package is sealed until it is opened by the consumer. Over time, a substantial amount of oxygen may enter the package as ingress oxygen. It is therefore desirable to remove the relatively small amount of head space oxygen quickly, before the high oxygen concentration can damage or degrade the packaged product, and to remove ingress oxygen more slowly but continuously while the package is on the shelf, to prevent a significant buildup of oxygen over time. A package capable of quickly removing head space oxygen and absorbing ingress oxygen over time would provide significant protection for oxygen-sensitive products.
In the food packaging industry, several means for limiting oxygen contamination in a packaged product have been developed. For example, products may be packaged under a modified atmosphere (called “modified atmosphere packaging” or MAP), or packaged in a vacuum. In these techniques, reduced oxygen environments are employed in the packaging process which reduce or eliminate contamination from head space oxygen. However, MAP or vacuum packaging processes are costly and do not prevent later contamination from ingress oxygen. In fact, a package with a partial or full vacuum would likely increase the oxygen permeation rate of the package walls.
In barrier film packaging processes, materials are used in the package walls which physically prevent oxygen from entering the package interior. Such processes, however, do not prevent contamination by head space oxygen, or prevent ingress of oxygen from holes or voids in the package seals. Furthermore, making a package wall completely impermeable to oxygen is often prohibitive, for example, in increased cost of materials and the unacceptably high weight and rigidity of the package. Therefore, a commercially viable package will typically have some degree of contamination from ingress oxygen.
Another means for limiting oxygen exposure in a package involves incorporating an oxygen scavenger in the packaging structure. An oxygen scavenger is a substance that consumes, depletes, or reduces the amount of oxygen from a given environment.
For example, an oxygen scavenging material may be included within the package cavity as a sachet. Insertion of sachets requires additional operations in the packaging process, thus increasing cost and production time. Sachets also take up space normally occupied by product. And while sachets may be effective at scavenging head space oxygen, they cannot stop ingress oxygen from entering the package and contacting the product before being scavenged. Furthermore, the use of sachets causes safety concerns, as the end-user may inadvertently consume the sachet along with the packaged product.
Alternatively, an oxygen scavenger may be incorporated into the packaging structure itself, for example by constructing the package walls with an oxygen scavenging polymer. Previous packaging systems incorporating oxygen scavenging materials use only one such material in a given package, thus producing a package with homogeneous oxygen scavenging properties.
U.S. Pat. No. 5,211,875 to Speer et al. discloses oxygen scavenger compositions comprising substituted or unsubstituted ethylenically unsaturated hydrocarbon polymers and a transition metal catalyst, which are activated on exposure to actinic radiation or an electron beam. These compositions are used to construct food packaging material with uniform oxygen scavenging properties.
U.S. Pat. No. 5,639,815 to Cochran et al. discloses a package wall comprising a single composition of an oxidizable polymer and a transition metal catalyst. The polymer/catalyst composition acts as an oxygen scavenger, and thus the package wall has homogeneous oxygen scavenging properties.
U.S. Pat. No. 5,700,554 of Speer et al. discloses an article useful for packaging oxygen-sensitive products, which contains an ethylenically unsaturated hydrocarbon polymer and a transition metal salt catalyst. Again, a given article contains only a single polymer/catalyst composition, and thus the oxygen scavenging properties of the package are homogeneous.
U.S. Pat. No. 5,776,361 to Katsumoto et al. discloses an oxygen scavenging composition or system for use in packaging oxygen-sensitive products, comprising at least one polyterpene and at least one catalyst. These packages also employ a single polyterpene composition in a given package, producing packages having homogeneous oxygen scavenging properties.
The packages disclosed in the U.S. Patents listed above may be engineered to have certain overall oxygen scavenging properties, so that either (but not both) the head space oxygen or ingress oxygen is optimally removed. Alternatively, materials with intermediate oxygen scavenging properties may be used in a given package to simultaneously combat both head space oxygen or ingress oxygen contamination, resulting in the suboptimal removal of oxygen from either source. What is needed, therefore, is a package with differential oxygen scavenging properties, which allows for the effective removal of both head space and ingress oxygen.
DEFINITIONS
“Head space oxygen” is the oxygen remaining in the package after the product has been sealed within the packaging materials.
“Ingress oxygen” is the oxygen which diffuses directly through the package walls or enters the package through voids or holes in the package.
“Oxygen scavenger” or “oxygen scavenging material” is a substance that consumes, depletes or reduces the amount of oxygen from a given environment.
“Oxygen scavenging capacity” (hereinafter “capacity”) is the total amount of oxygen consumed per unit mass of scavenging material. Typical units of capacity are cubic centimeters (cc) of oxygen per gram of material.
“Oxygen scavenging rate” (hereinafter “rate”) of an oxygen scavenging material is the amount of oxygen consumed per unit time per unit mass of scavenging material. Typical units of rate are cc/g/day.
“High rate oxygen scavenging materials” or “high rate materials” are oxygen scavengers chosen or designed to scavenge head space oxygen. “Low rate oxygen scavenging materials” or “low rate materials” are oxygen scavengers chosen or designed to scavenge ingress oxygen. Although generally high rate materials scavenge oxygen at faster rate than low rate materials, it is understood that there may be some overlap in the rates of high and low rate oxygen scavenging materials.
“Oxygen permeation rate” or “oxygen permeance” is the rate of diffusion of oxygen through a package wall at a certain pressure as measured in the absence of oxygen scavenging. Typical units of oxygen permeance are cc/[m
2
atm day].
SUMMARY OF THE INVENTION
In one aspect of the invention, there are provided packages for oxygen-sensitive products comprising at least two oxygen scavenging materials with different oxygen scavenging properties. The oxygen sca
Drinker Biddle & Reath LLP
Pyon Harold
Simone Catherine A.
Sonoco Development Inc.
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