Polymer compositions containing oxygen scavenging compounds

Details Polymer compositions containing oxygen scavenging compounds Polymer compositions containing oxygen scavenging compounds

1997-01-15

2002-05-21

Pyon, Harold (Department: 1772)

Stock material or miscellaneous articles

Hollow or container type article

Polymer or resin containing

C252S188280, C252S400100, C252S407000

Reexamination Certificate

active

06391406

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates to a polymer composition containing oxygen scavenging compounds therein, for use in packaging beverages, foods, pharmaceuticals and the like. In particular, these polymer compositions have utility as liners or gasketing materials for crowns, closures, lids or caps of various containers such as bottles or cans to prevent oxygen ingress and to scavenge oxygen which is present inside the container, or contained in outside air leaking past or permeating through the polymer composition. These polymer compositions may also be used in the construction of the container, as the container material itself, as a component of a container, or as a barrier layer thereupon or therein, to prevent oxygen ingress therethrough or to scavenge oxygen therein.
In packaging oxygen sensitive materials such as foodstuffs, beverages, and pharamceuticals (collectively “products”) oxygen contamination can be particularly troublesome. Care is generally taken to minimize the introduction of oxygen or to reduce the detrimental or undesirable effects of oxygen on the foodstuff or beverage.
Molecular oxygen (O
2
) can be reduced to a variety of intermediate species by the addition of one to four electrons; these species are superoxide, hydroxy radical, hydrogen peroxide, and water. O
2
and water are relatively unreactive: the three intermediate species are very reactive. Also, O
2
can be activated to singlet electron state oxygen (which can undergo subsequent reduction to the more reactive oxygen species) by irradiation, or by the presence of catalytic agents. These reactive oxygen species are free radical in nature, and the oxidative reactions in which they participate are therefore autocatalytic.
Carbon-carbon double bonds are particularly susceptible to reaction with the intermediate species. Such carbon-carbon bonds are often found in foods and beverages, pharmaceuticals, dyes, photochemicals, adhesives, and polymer precursors. Virtually any product which has complex organic constituents will contain such carbon-carbon double bonds or other oxygen reactive components, and hence can undergo oxidative reactions. Thus, if the oxidation products adversely affect the performance, odor or flavor of the product, then removing the oxygen which is present (either dissolved in or trapped with the product), preventing oxygen ingress, or inhibiting the reactions of oxygen will benefit the product.
A number of strategies exist to deal with oxygen as a contaminant. The most basic is simply to remove oxygen from the product by vacuum or by inert gas sparging, or both. Such systems are used in boiler water treatment, the orange juice and brewing industries, and in modified-atmosphere packaging of food products. This technology, while somewhat equipment intensive, can remove about 90-95% of the oxygen present in air from the product (or its container) prior to or during packaging. However, the removal of the remaining 5-10% of oxygen using this approach requires longer times for vacuum treatment and/or sparging and increasingly larger volumes of higher and higher purity inert gas which must not itself be contaminated with trace levels of oxygen. This makes the removal (by such methods) of the last traces of oxygen expensive. A further disadvantage of these methods is a tendency to remove volatile product components. This is a particular problem with foods and beverages, wherein such components are often responsible for some or all of the aroma and flavor.
Herein, the term “oxygen scavenger’ means materials or chemical compounds which can:
a) remove oxygen from the interior of a closed package by reacting or combining with entrapped oxygen or with oxygen that is leaking into the package interior past the package/closure sealant or gasket;
b) prevent or reduce the perfusion of oxygen through the gasketing/sealant materials between container and closure;
c) prevent or reduce the perfusion of oxygen through the materials of the package/closure itself by incorporation of the oxygen scavenger into the materials of which the container/closure is/are made;
d) prevent or reduce the perfusion of oxygen through the material of the package/closure itself by incorporation of the oxygen scavenger into one or more layers of a multilayer container/closure construction.
The term “antioxidants” as used herein means materials or compounds which, when added to the foodstuff or beverage itself, slow the rate of oxidation or otherwise reduce the undesirable effects of oxidation upon the foodstuff or beverage.
For example, it has been known since the 1930's that oxygen in beer adversely affects its flavor and stability. Amounts of oxygen as low as 0.1 to 0.2 ml per 355 ml container will, over time, cause darkening of the beer, an increase in chill-haze values and significant taste changes. Oxygen's effect on beer is so strongly detrimental that many brewers go to great lengths to remove it from the bottle during the filling process. One usual technique is to (1) remove the air (via vacuum) from a clean bottle; (2) fill the bottle with CO
2
; (3) flow the beer down the bottle wall into the bottle thus displacing the CO
2
; and (4) finally, to squirt a jet of high-pressure deoxygenated water into the bottle to cause the beer to over-foam just as the cap is put on (attempting thereby to displace the remaining headspace gases with the beer's own CO
2
). In addition, to minimize introduction of air (21% O
2
) into the headspace just before capping, production lines are run more slowly than otherwise necessary. All this is expensive, and usually reduces the total O
2
concentration in the headspace to only about 200-400 parts per billion: the desired level is as close to zero as possible, but certainly below about 50 ppb. The 200-400 ppb achieved in the packaged product by careful brewers corresponds to approximately 50-100 microliters of oxygen per 355 ml bottle. Even this small quantity of oxygen is still considered to be one of the major limitations on quality and shelf life of beer today.
Many other food products suffer similar oxygen-mediated degradation; for example, individual portions of prepared foods are marketed in containers made of plastics, and air entrapped therein, and leaking or perfusing into the package after processing, is an acknowledged industry problem. This leakage or perfusion is often especially true for packages made entirely of plastics, because many plastics with otherwise desirable properties are relatively permeable to oxygen. Incorporation of the present invention into the bulk of such plastics, or into one or more layers of a multilayer package, could be beneficial in reducing or eliminating such perfusion. Among obvious benefits of such applications of the invention is extended shelf life.
None of the above techniques remove or control (a) oxygen dissolved in the product (which will outgas into the headspace as the enclosed system comes to equilibrium), or (b) oxygen leakage into the package past the gasket/container interface, or (c) oxygen permeating through the gasket into the interior of the package, or (d) oxygen permeating through the container itself into the package. The present invention also aids in removal of O
2
from these other three sources. Furthermore, it is known that free oxygen inside a package may yield very rapid degradation of the product, consequently a desired property of any scavenger is to remove most of the free oxygen as quickly as possible (i.e., ultimate O
2
absorption capability is subordinate to fast uptake kinetics).
Antioxidants (such as sulfur dioxide, trihydroxy butyrophenone, butylated hydroxy toluene and butylated hydroxy anisole) and oxygen scavengers (such as ascorbic acid, isoascorbic acid and glucose oxidase-catalase) have been used in an attempt to reduce the effects of oxygen contamination on beer (See e.g., Reinke et al., “Effect of Antioxidants and Oxygen Scavengers on the Shelf-life of Canned Beer,” A.S.B.C. Proceedings, 1963, pp. 175-180, Thomson, “Practical Control of Air in Beer”, Brewer&apos

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