Stock material or miscellaneous articles – Hollow or container type article – Polymer or resin containing
Reexamination Certificate
2000-02-11
2003-01-14
Michl, Paul R. (Department: 1714)
Stock material or miscellaneous articles
Hollow or container type article
Polymer or resin containing
Reexamination Certificate
active
06506463
ABSTRACT:
STATEMENT REGARDING FEDERALLY FUNDED RESEARCH
(Not Applicable)
FIELD OF THE INVENTION
The invention generally relates to compositions, articles, and methods for packaging oxygen-sensitive substances, especially comestible products. The invention is directed to oxygen barrier materials having improved passive oxygen barrier properties and also having active oxygen scavenger properties. The active oxygen scavengers of this invention are condensation copolymeric substances which can be used for bottles and packaging and have the ability to consume, deplete or reduce the amount of oxygen in or from a given environment in the solid state at ambient temperatures. Formulations are disclosed which may be fabricated into plastic bottles and other packaging articles and films.
BACKGROUND OF THE INVENTION
Plastic materials have continued to make significant advancements into the packaging industry due to the design flexibility of their material and their ability to be fabricated in various sizes and shapes commonly used in the packaging industry. The deployment of plastic materials into packaging articles such as films, trays, bottles, cups, bowls, coatings and liners is already commonplace in the packaging industry. Although plastic materials offer the packaging industry many benefits with an unlimited degree of design flexibility, the utility of plastic materials has remained inhibited in situations where barrier properties to atmospheric gases (primarily oxygen) are necessary to assure adequate product shelf life. When compared to traditional packaging materials such as glass and steel, plastics offer inferior barrier properties which limits their acceptability for use in packaging items that are sensitive to atmospheric gases, particularly when the exposure to the atmospheric gases will entail extended time periods. The packaging industry continues to seek packaging materials which offer the design flexibility of plastics and at the same time have the barrier properties of glass and steel.
The packaging industry has developed technology to improve the barrier properties of plastic containers by developing containers that offer improved barrier properties approaching, but not comparable to, those of glass, steel, and aluminum. By a very wide margin, polyethylene terephthalate (PET) and similar packaging polyesters have gained wide acceptance, especially for bottling applications, in view of the clarity and rigidity associated with PET bottles. PET has made significant inroads into bottling and packaging applications at the expense of the use of glass containers but primarily in applications where the needs for barrier properties are modest. A significant example is the use of PET for soft drink bottles. However, PET barrier properties have limited its use in the packaging of oxygen sensitive products.
It is generally accepted in the packaging industry that polyamides have superior passive oxygen barrier properties when compared to similar polyester packaging constructions. A useful passive oxygen barrier polymer is one that exhibits the ability to retard the permeability of oxygen through it when compared with the permeability of oxygen through other resins. Further, it has been reported that a polyamide known as MXD-6 has some active oxygen barrier capacity. MXD6 is poly(m-xyleneadipamide) which is a polyamide made from equal molar amounts of the two monomers (1) meta-xylenediamine and (2) adipic acid. An active oxygen barrier resin is a substance capable of intercepting and scavenging oxygen (by undergoing chemical reaction with the oxygen) as it attempts to pass through the packaging. This method also affords the opportunity to eliminate unwanted oxygen from within the package cavity wherein said oxygen may have been inadvertently introduced during packaging or filling. This method of providing oxygen barrier properties where a substance consumes or reacts with the oxygen is known as an “active oxygen barrier” and is a different concept from passive oxygen barriers which attempt to hermetically seal a product away from oxygen via the passive approach.
When MXD-6 (about 4 wt %) is blended with PET (about 96 wt %), the resulting blend is about 70% as permeable to oxygen as a similar construction of unmodified PET. Presumably, this 30% improvement over unmodified PET may be attributed to the improvement in passive barrier properties of the aforementioned blend. When an oxidation catalyst is added to the blend (e.g., about 50-200 PPM cobalt with respect to the weight of the blend), the blend takes on enhanced active oxygen scavenging properties. The O
2
permeability of the blend is diminished under these conditions until the active O
2
scavenging capacity of the blend is depleted. The barrier properties achieved by the blend are suitable only for less demanding packaging requirements and then only with very heavy use of the blend. However, MXD-6 is a relatively expensive polyamide and the use of large amounts of it in a package serves to undermine the economic viability of such packaging. Lower cost, more common polyamides, such as the well known poly(hexamethyleneadipamide) have the improved passive barrier properties of polyamides but are devoid of active barrier properties. What is needed is an active-passive polyamide oxygen barrier polyamide-based resin which may be produced at reasonable cost and which has sufficient oxygen scavenging and barrier properties to offer the possibility of target shelf lives in the range of 6 months to two years for oxygen sensitive products. This invention addresses such need.
INVENTION SUMMARY AND REVIEW OF PRIOR ART
In a commonly assigned and co-pending application filed on Sep. 23, 1996 and having Ser. No. 08/717,370, it was disclosed that certain hydrocarbons, such as polyolefins, (especially polydienes) when present in small amounts as polyolefin oligomer blocks in a block copolyester polymer added substantial active oxygen scavenging capacity to packaging polyesters which showed no active oxygen scavenging capacity what-so-ever in the absence of the polyolefin oligomer blocks. The oxygen scavenging copolyesters of the above-referenced application were comprised predominantly of packaging polyester segments with only an oxygen scavenging amount of polyolefin oligomer segments present to supply the oxygen scavenging capacity required for the intended packaging application. The copolyesters of the application having Ser. No. 08/717,370 were typically in the range of about 0.5-12 wt % polyolefin oligomer segments with the remainder comprising polyester segments. An especially preferred embodiment was a copolyester of about 4 wt % polyolefin oligomer segments with the remainder being polyester segments. Such block copolyesters comprising low weight percent levels of polyolefin oligomer segments have properties (such as melting point, viscosity, and clarity) very similar to the unmodified polyester from which the polyester segments were derived. In particular, layers in laminar packages and bottles having one or several layers of unmodified polyester and one or several layers of oxygen scavenging block copolyester as described above, were self-adherent and packaging articles appeared to be a monolithic (rather than layered) construction.
For this invention, applicants have extended the concept of implanting high capacity oxygen scavenging polyolefin oligomer segments into polyamides forming block copolyamides comprising predominantly polyamide segments and an oxygen scavenging amount of polyolefin oligomer segments. As was the case for the copolyesters disclosed in the application having Ser. No. 08/717,370, the copolyamides of this invention have properties very similar to the polyamide from which the polyamide segments were derived. A typical use for such polyamides comprises a layered construction such as a package film or bottle wall having outer and inner layers of polyamide and a middle layer of copolyamide (wherein the polyamide segments of the copolyamide are derived from those of the inner and/or outer layer polyamides and the oxygen scav
Cahill Paul J.
Richardson Joel Albert
Wass Raymond V.
BP Corporation North America Inc.
DiSalvo Joseph
Michl Paul R.
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