Stock material or miscellaneous articles – Hollow or container type article – Polymer or resin containing
Reexamination Certificate
2000-02-11
2002-02-12
Kiliman, Leszek (Department: 1773)
Stock material or miscellaneous articles
Hollow or container type article
Polymer or resin containing
C428S474400, C525S168000, C525S171000, C525S177000, C525S445000, C528S298000, C252S186100
Reexamination Certificate
active
06346308
ABSTRACT:
STATEMENT REGARDING FEDERALLY FUNDED RESEARCH
(Not Applicable)
FIELD OF THE INVENTION
The invention generally relates to compositions having active oxygen scavenging capacity and the use of these compositions for improved packaging of oxygen sensitive substances. Formulations are disclosed which may be fabricated into packaging articles or used as container liners/coatings.
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, steel or aluminum, 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, steel or aluminum.
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, particular polyesters such as polyethylene terephthalate (PET) have found wide acceptance in the packaging industry and are moderately good passive oxygen barriers. Polyamides, such as polyhexamethyleneadipamide 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, consumption of a material incorporated in the package. 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.
Active oxygen scavengers are known and have been used in a variety of constructions. Optimally, active oxygen scavengers should have as many as possible, or at least some, of the features recited below:
(1) Their oxygen scavenging ability should be present both in the absence and/or in the presence of water or moisture.
(2) They should have clarity similar to that of PET or other packaging thermoplastics when necessary for production of clear bottles or films.
(3) They should be self-adherent to adjacent layer(s) when used as layer(s) in a multi-layer package construction.
(4) They should be evenly dispersed throughout the package so as to afford optimum and uniform opportunity to scavenge oxygen.
(5) They should have glass transition temperatures above filling and storage temperatures (at least above about 30° C.) so that they exist as solids or solid films for these purposes.
(6) When used as a container liner, they should be capable of being sprayed onto the inner surface of a container from an aqueous system (as opposed to a lacquer which would require evaporation of organic solvents).
(7) The decomposition products to which the active oxygen scavengers are decomposed after reaction with oxygen must not be deleterious to the packaged product or must be shielded from the packaged product.
(8) The mechanism of their reaction with oxygen must not be deleterious to the strength, clarity, or other salient features of the packaging article.
What is needed are active oxygen barrier materials possessing as many as possible of the features recited above, which may be produced at reasonable cost, and which have sufficient oxygen scavenging and barrier properties to offer the possibility of target shelf lives in the range of six months to two years for oxygen sensitive products. This invention further addresses such need.
INVENTION SUMMARY AND REVIEW OF PRIOR ART
In a commonly assigned, related, and co-pending US application filed on Sep. 23, 1996 and having Ser. No. 08/717,370, now U.S. Pat. No. 6,083,585 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 now U.S. Pat. No. 6,083,585 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.
In related PCT Application Number PCT/US98/02991 which was filed on Feb. 17, 1998 the concept of implanting high capacity oxygen scavenging polyolefin oligomer segments was extended to polyamides. The above referenced PCT application disclosed block copolyamides comprising predominantly polyamide segments and an oxygen scavenging amount of polyolefin oligomer segments. As was the case for the earlier disclosed copolyesters, the corresponding copolyamides had properties very similar to unmodified polyamides, especially the polyamide from which the polyamide segments were derived. Polyamides are generally considered to be an inherently superior passive barrier as compared to polyesters. Thus copolyamides not only had substantial active oxygen scavenging capacity but also had improved passive barrier properties since they were comprised mainly of polyamide segments. In this application, additional oxygen scavenging moieties are disclosed which when incorporated i
Barski, Jr. Roman F.
Cahill Paul J.
Nyderek Walter M.
Richardson Joel A.
Rotter George E.
BP Corporation North America Inc.
DiSalvo Joseph
Kiliman Leszek
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