Stock material or miscellaneous articles – Hollow or container type article – Polymer or resin containing
Reexamination Certificate
1998-12-22
2002-06-18
Michl, Paul R. (Department: 1714)
Stock material or miscellaneous articles
Hollow or container type article
Polymer or resin containing
C528S50200C
Reexamination Certificate
active
06406766
ABSTRACT:
STATEMENT REGARDING FEDERALLY FUNDED RESEARCH
(Not Applicable)
FIELD OF THE INVENTION
The invention generally relates to copolymer compositions having active oxygen scavenging capacity and the use of these compositions for improved packaging of oxygen sensitive substances. Improved formulations are disclosed which may be fabricated into packaging articles. Also disclosed are improved packaging article constructions and embodiments.
BACKGROUND OF THE INVENTION
This application and the related applications, as recited above, are generally directed to active oxygen scavenging copolymers and their use in packaging articles. Most embodiments disclosed in this and the related applications involve the use of the active oxygen scavenging copolymers in a laminar composite as at least one of several layers comprising the wall or film of a packaging article.
The active oxygen scavenging copolymers of this and the related applications are typically copolycondensates comprising predominantly polycondensate segments and a lesser amount of oxygen scavenging moiety (OSM) segments. It is a common practice to use copolymers, more specifically copolycondensates, as packaging and bottling materials, For example, even common polyethylene terephthalate (PET) bottles used for bottling soda pop often comprise some isophthalic linkages in the polymer and thus could be called a copolymer. In order to avoid such ambiguities, the term oxygen scavenging copolymer or modified copolymer will be used to designate those polymers which have OSM segments and which are an important component of this invention. The oxygen scavenging modified copolymers of this invention are prepared as thermoplastics in that they are suitable for melt processing into bottles and packaging articles. However, applications for these materials are envisioned where the thermoplastic material may subsequently be transformed into a thermoset resin.
It is known that post polymerization treatment of modified packaging and bottling polycondensates (i.e., those which have not been modified so as to add oxygen scavenging ability) may generally improve the salient packaging characteristics of such materials. The post polymerization treatment may involve heat and/or chill treatment, chemical treatment/reaction, irradiation, aging, or combinations thereof. A non-exhaustive list of improvements which may be realized includes devolatization, drying, increased crystallization, further polymerization (especially solid state polymerization), increased intrinsic viscosity (IV), increased molecular weights, improved odor and/or taste, improved passive barrier properties, and improved clarity. The application of post polymerization treatment techniques to unmodified polycondensate to obtain such improvement is relatively well known in the art. Application of these post polymerization techniques to active oxygen scavenging copolymers in a manner similar to the techniques used on unmodified polycondensates has here-to-fore proven unsatisfactory because of problems encountered such as loss of oxygen scavenging capacity and discoloration or loss of clarity of the oxygen scavenging copolymers. What is needed are methods for post polymerization treatment of oxygen scavenging copolymers which provide the desired improvements gained for unmodified polycondensates but which avoid the problems previously encountered for post polymerization treatment of oxygen scavenging copolymers. This application addresses these and other needs leading to improved active oxygen scavenging copolymers and packaging articles made therefrom.
INVENTION SUMMARY AND REVIEW OF PRIOR ART
For more complete understanding of this and the related applications, it should be recognized that there are two broad types of barriers for shielding packaged oxygen sensitive substances from oxygen (generally oxygen from air). One is known as a passive oxygen barrier and finds utility because of superior resistance to the permeation of oxygen through such constructions. Glass and metal are essentially perfect passive oxygen barriers. Condensation polymers, especially polyesters such as polyethylene terephthalate (PET), have found wide acceptance in the packaging industry and are moderately good passive oxygen barriers. Other condensation polymers may exhibit either superior or inferior passive barrier properties than those of polyesters. For example, polyamides, such as polyhexamethylene adipamide and polyphthalamides, are generally better passive oxygen barriers than polyesters when deployed in similar constructions.
The other type of oxygen barrier is known as an active oxygen barrier. An active oxygen barrier is a substance capable of intercepting and scavenging oxygen (by undergoing chemical reaction with the oxygen), for example, as the oxygen attempts to permeate through the packaging. A major salient feature of active oxygen scavengers is their ability not only to intercept oxygen from air as it attempts to reach the package cavity but also to provide the means to eliminate unwanted oxygen (often called head space oxygen) from within the package cavity wherein said oxygen may have been inadvertently introduced during packaging or filling. Only active oxygen scavengers can remove unwanted oxygen from the package cavity. Active oxygen scavenging implies, therefore, transformation of a material incorporated in the package as it reacts with and depletes oxygen. The material is progressively consumed so that the active oxygen scavenging ability is eventually depleted or at least diminished. However, this eventual depletion of the active oxygen scavenging moiety can be adjusted so that the depletion occurs only well after the required oxygen free shelf life of the packaged product which is typically one year or less.
The active oxygen scavenging copolymers of this and the related applications are typically copolycondensates comprising predominantly polycondensate segments and a lesser amount of oxygen scavenging moiety (OSM) segments. Predominantly, as used above, means over 50 wt % of the copolymer is comprised of polycondensate segments. Comprising as used in this application is defined as “specifying the presence of stated features, integers, steps, or components as recited, but not precluding the presence or addition of one or more other steps, components, or groups thereof”. Comprising is different from “consisting of” which does preclude the presence or addition of one or more other steps, components, or groups thereof. The polycondensate segments of the oxygen copolymers are typically polyester (especially comprising PET) or polyamide, but polysulfones, polyethers, polyketones and other polycondensates are also envisioned as sources of polycondensate segments for the oxygen scavenging copolymers of this application. The OSM segments of the oxygen scavenging copolymers are typically polyolefin oligomers, polypropylene oxide oligomers, or methyl pendant aromatic compounds as defined in the related application having Application Number PCT/US98/05239. The wt % of OSM segments employed in the copolymers is usually in the range of about 0.5 to 12 wt % and preferably in the range of about 2 to about 8 wt %. The copolymers may be produced by any means but are typically made by placing terminal functional group(s) on the OSM which are capable of entering into polycondensation, transesterification, transmigration, and similar transfer reactions. The required amount of these functionalized OSM's are then used as a “pseudo monomer” in a batch or continuous polycondensation or reacted with a previously prepared polycondensate where they are incorporated into the polymer by transesterification thus producing the active oxygen scavenging copolymer.
In selected applications, such as for packaging non-comestible products such as electronic components, the oxygen scavenging copolymers may be deployed as a single layer of film to form the packaging article. More often, the oxygen scavenging copolymer comprises at least one layer of a multi-layered packaging article. In many embodiments, at least one of t
Barnes Tamila J.
Bauer Charles W.
Cahill Paul J.
Johnson David C.
Kulzick Matthew A.
BP Corporation North America Inc.
DiSalvo Joseph
Michl Paul R.
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