Compositions – Reductive bleachant – deoxidant – reductant – or generative – Deoxidant or oxygen scavenging
Reexamination Certificate
2001-11-30
2004-11-16
Anthony, Joseph D. (Department: 1714)
Compositions
Reductive bleachant, deoxidant, reductant, or generative
Deoxidant or oxygen scavenging
C428S034200, C428S034300, C428S035200, C428S035400, C428S036600, C428S036700
Reexamination Certificate
active
06818151
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to the field of oxygen barrier polymers. More particularly, it concerns oxygen barrier compositions and packaging articles comprising a copolymer that comprises (1) repeating units derived from vinylidene chloride and (2) repeating units comprising an oxygen scavenging moiety.
2. Description of Related Art
Due at least in part to their ability to be fabricated into packaging articles of various sizes and shapes (e.g., their design flexibility), plastic materials, such as organic polymers, are becoming increasingly important in the packaging industry. The use of organic polymers in films, bottles, coatings, and liners has become commonplace in packaging. However, while the use of organic polymers has expanded in many areas, their usefulness has been limited in packaging requiring good barrier properties to atmospheric gases (primarily oxygen). This has been because the barrier properties of available organic polymers have not been able to approach the barrier properties of traditional packaging materials, such as glass and metal. New materials having enhanced barrier performance, while retaining benefits inherent to organic polymers would be useful both to the packaging and plastic manufacturing industries.
Organic polymers can be classified by how permeable they are to gases (e.g., oxygen or carbon dioxide) and moisture vapor. Those organic polymers that significantly restrict the ability of gases to pass through them are referred to as gas barrier polymers or high barrier polymers. The use of high barrier polymers is very important in the packaging of certain foods and beverages, which require protection from oxygen and moisture. Vinylidene chloride based polymers (PVDC) and copolymers were discovered some time ago, and they are among the most widely used high oxygen barrier resins. Perhaps the most familiar examples of the vinylidene chloride based polymers used in packaging are commercial Saran® products. Other high oxygen barrier polymers also widely used, include ethylene vinyl alcohol (EVOH) copolymers. However, EVOH copolymers lack the moisture resistance properties associated with vinylidene chloride based polymers, and therefore, EVOH copolymers are often combined with additional moisture barrier polymers in packaging structures. Packaging comprising high gas barrier polymers, such as PVDC and EVOH, can be inadequate in protecting certain packaged oxygen sensitive products, such as beer and juice, from environmental oxygen. This has prompted extensive efforts to modify organic polymers or packaging structures made from them to enhance oxygen barrier properties. Such efforts have included chemical modification of organic polymers (e.g., fluoridation or sulfonation of organic polymers), and structural variation in packaging design.
For example, “hybrids” having improved gas barrier performance have been developed. The hybrids involve thin-layer surface coating or deposition of silica or graphite over an organic polymer substrate. Other developments have involved inorganic-organic alloys (nanocomposites) comprising gas impermeable inorganic fillers dispersed in an organic polymer matrix. This technology has resulted in enhanced gas barrier performance as the result of the “tortuous path effect,” however these approaches have had limited commercial success due to the cost associated with the additional fabrication steps involved. Thus, it would be desirable to be able to structurally modify PVDC based polymers in such a way that their oxygen barrier performance approaches that of traditional materials, such as glass and metal, for use in more demanding packaging applications.
PVDC based polymers are among the best oxygen barrier polymers, but as discussed above they can be inadequate for use in certain packaging applications for oxygen sensitive food and beverages. PVDC homopolymer is rarely used as a packaging material by itself due to its narrow melt processing temperature. However various PVDC copolymers that comprise small amounts of a comonomer, such as vinyl chloride, methylacrylate or acrylontrile have had some commercial success. While these copolymers offer the desired melt process capability due to their reduced melting points, their gas barrier performance is compromised due to their decreased crystallinity and due to dilution of the vinylidene chloride. Thus, from both a technological and commercial point of view, it would be highly desirable to enhance the gas barrier properties of polymers that are commercially available (e.g., PVDC), while improving their processability.
Another approach to providing packaging for oxygen sensitive products involves inorganic and/or organic oxygen scavengers being used in packaging structures to eliminate or reduce the oxygen inside a package. Oxygen scavengers that can be used include iron powders and unsaturated olefinic polymers. In oxygen scavenging packaging, oxygen within the package or that diffuses through the packaging wall from the outside environment is removed by the irreversible reaction of the oxygen scavenger with the oxygen. In the case of polymeric oxygen scavengers, the oxygen scavenging functionality can be an unsaturated olefinic moiety, which can be incorporated into or grafted onto a polymer. Because these polymers were developed to aid in the removal of headspace oxygen from a package, they typically have relatively high oxygen transmission rates, so that the oxygen within the headspace can easily reach the reactive site (scavenging site) and so that it is reacted at a sufficiently rapid rate. Therefore, most oxygen scavenging polymers used in packaging, such as polyolefins and acrylate polymers, have relatively high oxygen transmission rates and/or relatively low oxygen barrier properties. Oxygen scavenging polymers obtained by grafting cycloalkenyl molecules onto an ethylene-methylacrylate polymer via a reactive extrusion process (Ta Yen Ching et al., Patent Application WO99/48963) represent a significant development in the field of oxygen scavenging packaging. An important advantage of this type of oxygen scavenging polymer is that the oxygen scavenging functionality is based on a cycloalkenyl moiety, which does not result in volatile by-products being formed from the oxygen scavenging reaction.
SUMMARY OF THE INVENTION
In the development of new packaging materials, the properties of processability and product performance have typically been found to be interrelated, so that often a compromise has had to be reached favoring one property over the other. This is exemplified in the way in which commercial PVDC copolymers have evolved through the chemical modification of PVDC homopolymer. Commercially successful PVDC copolymers have been made by incorporating small amounts of a comonomer into PVDC polymers improving their processability, however the new copolymers have reduced gas barrier properties as compared to PVDC homopolymer.
The present invention is directed to a novel approach to chemically modifying the PVDC polymer structure that achieves both enhanced oxygen barrier performance and good processability (due to decreased melting point). The present invention is based on the surprising discovery that an oxygen-scavenging vinyl cycloalkenylacrylate monomer can be successfully incorporated into the polymer structure of PVDC by free radical polymerization. The oxygen scavenging vinyl cycloalkenylacrylate monomer has two carbon-carbon double bonds, one in the vinyl moiety of the monomer and the other in the cycloalkenyl moiety of the monomer. The polymerization of vinylidene chloride with the cycloalkenyl acrylate monomer is believed to proceed primarily through reaction of the vinyl double bond of the oxygen scavenging monomer with the carbon-carbon double bond of the vinylidene chloride. Reaction of vinylidene chloride with the double bond of the cycloalkenyl moiety of the oxygen scavenging monomer is believed to be minimal during the polymerization reaction.
The successful incorporation of the vinyl cyc
Cai Kevin
Ching Ta Yen
Torres Lennard
Yang Hu
Anthony Joseph D.
Chevron Phillips Chemical Company LP
Williams Morgan & Amerson P.C.
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