Compositions – Reductive bleachant – deoxidant – reductant – or generative – Deoxidant or oxygen scavenging
Reexamination Certificate
1999-03-24
2001-07-03
Seidleck, James J. (Department: 1711)
Compositions
Reductive bleachant, deoxidant, reductant, or generative
Deoxidant or oxygen scavenging
C252S188100
Reexamination Certificate
active
06254803
ABSTRACT:
FIELD OF THE INVENTION
The present invention is directed to oxygen scavengers for use in plastics materials, and in particular plastics films. Emphasis is given to scavengers which produce low or negligible levels of oxidation by-products which may contaminate the head space in a package.
BACKGROUND OF THE INVENTION
The majority of plastic films produced are employed in some form of packaging. The present invention is primarily concerned with those films used for applications requiring a low level of oxygen in a package, though may also find other uses. Primarily this type of packaging includes comestibles such as meat, which are often packaged to have a low oxygen environment.
Limiting the exposure of oxygen-sensitive products to oxygen maintains and enhances the quality and shelf life of many products. For instance, by limiting the oxygen exposure of oxygen-sensitive food products in a packaging system, the quality of the food product can be maintained and spoilage retarded. In addition, such packaging also keeps the product in inventory longer, thereby reducing costs incurred from waste and having to restock.
In the food packaging industry, several techniques for limiting oxygen exposure have been developed. Common techniques include those where oxygen is consumed within the packaging environment by some means other than the packaged article or the packaging material (e.g., through the use of oxygen scavenging sachets), those where reduced oxygen environments are created in the package (e.g., modified atmosphere packaging (MAP) and vacuum packaging), and those where oxygen is prevented from entering the packaging environment (e.g., barrier films).
The art dealing with barrier packaging, and the low oxygen or modified packaging of products is relatively well developed. This includes the use of films and inserts containing oxygen scavenging compounds able to extract a majority of any residual oxygen after packaging occurs.
Oxygen scavenging compounds for use in plastic films are relatively well known.
For instance:
Michael Rooney, “Oxygen scavenging: a novel use of rubber photo-oxidation”, Chemistry and Industry, Mar. 20, 1982, pp 197-198 describes the use of ethylenically unsaturated compounds as oxygen scavengers on exposure to light. However systems describing the use of transition metal catalysts are not described.
U.S. Pat. No. 4,908,151 to Mitsubishi, describes sachets containing unsaturated fatty acid (i.e. an ethylenically unsaturated hydrocarbon) in combination with a transition metal compound in a basic substance. However there is no description of these materials in the form of a film nor the use of photo-exposure as an initiating mechanism. The disadvantages of sachets include the need for additional packaging steps (to add the sachet to the package), the potential for contamination of the packaged article should the sachet break, and the potential of ingestion by a consumer.
Japanese patent JP5032277 to Kuwa describes the use of radical containing resin layers in packages. The invention comprises an oxidizable polymer whose oxygen scavenging abilities is photoinitiated.
New Zealand patent application NZ241802 to W. R. Grace and also NZ243077 also to W. R. Grace, claim oxygen scavenging compositions comprising ethylenically unsaturated hydrocarbons with transition metal catalysts. A wide range of ethylenically unsaturated compounds are discussed in the texts of these specifications though there is no mention of the problem to which the present invention is directed, nor the compounds and products encompassed by the present invention.
Oxygen scavenging materials also have been incorporated directly into the packaging structure. This technique (hereinafter referred to as “active oxygen barrier”) can provide a uniform scavenging effect throughout the package and can provide a means of intercepting and scavenging oxygen as it passes through the walls of a package, thereby maintaining the lowest possible oxygen level throughout the package. Active oxygen barriers have been formed by incorporating inorganic powders and/or salts as part of the package. See, e.g., U.S. Pat. Nos. 5,153,038, 5,116,660, 5,143,769, and 5,089,323. However, incorporation of such powders and/or salts can degrade the transparency and mechanical properties (e.g., tear strength) of the packaging material and can complicate processing, especially where thin films are desired. Also, these compounds as well as their oxidation products can be absorbed by food in the container, which can result in the food product failing to meet governmental standards for human consumption.
EP 0 519 616 discloses an oxygen scavenging composition that includes a blend of an epoxide, a first polymeric component grafted with an unsaturated carboxylic anhydride and/or acid, a second polymeric component including OH, SH, or NHR2 groups where R
2
is H, C
1
-C
3
alkyl, or substituted C
1
-C
3
alkyl moiety, and a metal salt capable of catalyzing the reaction between oxygen and the second polymeric component. The first polymeric component is present in an amount sufficient to ensure that the blend is non-phase separated. A blend of polymers is utilized to obtain oxygen scavenging, and the second polymeric component is preferably a (co)polyamide such as MXD6.
Another type of active oxygen barrier is illustrated in EP-A-0 301 719, EP-A-0 380 319, PCT publication no. WO 90/00578, and PCT publication no. WO 90/00504. See also U.S. Pat. Nos. 5,021,515, 5,194,478, and 5,159,005. The disclosed oxygen scavenger includes polyamide-transition metal catalyst compositions. Through catalyzed scavenging by the polyamide, the package wall regulates the amount of oxygen reaching the interior of the package. However, the onset of useful oxygen scavenging (i.e., up to about 5.8×10
−5
cm
3
/m
2
·s or 5 cm
3
/m
2
·24 hours at ambient conditions) can take as long as 30 days to occur. Therefore, this technique is not acceptable for many applications. Further, polyamides typically are incompatible with many thermoplastic polymers commonly used to make flexible packaging materials (e.g., ethylene/vinyl acetate copolymers, low density polyethylene, etc.) or, when used by themselves, are difficult to process and result in inappropriately stiff structures.
Oxygen scavenging compositions that include transition metal catalysts and ethylenically unsaturated hydrocarbon polymers which have an ethylenic double bond content of from 0.01 to 10 equivalents per 100 grams of polymer are disclosed in U.S. Pat. No. 5,399,289. Various conventional homopolymers, copolymers, and polymer blends are disclosed. Because these polymers are amorphous, they can be difficult to blend and process with film-forming semicrystalline polymers conventionally used to make flexible packaging materials.
The use of a transition metal and a photoinitiator to facilitate initiation of effective scavenging activity of ethylenically unsaturated compounds is taught in U.S. Pat. No. 5,211,875, which is incorporated herein by reference as if set forth in full.
PCT publication nos. WO 95/02616 and WO 96/40799 disclose a scavenger composition that includes a transition metal salt and a copolymer (of ethylene and a vinyl monomer) having ether, amino, carboxylic acid, ester, or amide functionalities pendent therefrom. Although these compositions can provide oxygen scavenging activity, the particular advantages of having ethylenic unsaturation contained within a cyclic moiety are not disclosed. Because the compositions of this invention are significantly cleaner than those described in the prior art, they do not require the use of high levels of adjuncts to absorb the undesirable byproducts. Such absorbent additives are known in the art, for example see U.S. Pat. No. 5,834,079 and U.S. Pat. No. 08/857,276. It is also well know in the art that such additives (zeolites and silicas) adversely effect the haze and clarity of packaging structures.
PCT Application WO 96/40799 describes the use of a variety of ethylenic materials with benzylic, allylic or ether containing side chains. Some
Depree Craig
Matthews Andrew E.
Cryovac Inc.
McClendon Sanza
Quatt Mark B.
Seidleck James J.
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