Stock material or miscellaneous articles – Hollow or container type article – Polymer or resin containing
Cain, Edward J. (Department: 1714)
Stock material or miscellaneous articles
Hollow or container type article
Polymer or resin containing
FIELD OF THE INVENTION
The invention relates to multilayered plastic containers having improved resistance to oxygen permeation and to compositions and processes for production of multilayered plastic bottles.
BACKGROUND OF THE INVENTION
In order to be technically acceptable, beer containers (glass, metal, or plastic) must maintain the beer contained therein in near oxygen free environment. A generally accepted industry standard is considered to be a maximum of 1 ppm oxygen ingress into the bottle over the planned shelf life of the bottled beer. Further, not only must oxygen be excluded from the bottled beer, but the egress of carbon dioxide from the beer out through the bottle walls must also be eliminated or at least contained to defined standards.
Oxygen may be present in bottled beer from at least three separate sources. In some instances, unwanted oxygen (from air) is not completely eliminated from the space above the liquid in the beer bottle during the bottle filling process. Oxygen arising from this source is known as head space oxygen. Even beer packaged in cans is susceptible to the presence of head space oxygen. In conventionally capped glass beer bottles, oxygen may enter the bottle during storage by permeation through the medium used as the gasket in the crimped bottle crown. A third source of oxygen in bottled beer is specific to the use of plastic bottles. Oxygen, from air, has the ability to permeate many conventional bottling polyesters and end up inside the bottle cavity. Also, for plastic bottles, oxygen may be dissolved or adsorbed in the plastic Oxygen dissolved in or adsorbed on the plastic bottle walls may be desorbed and end up in the bottle cavity. Such desorbed oxygen is indistinguishable from head space oxygen once inside the bottle cavity, except that it should be viewed as a possible continuing source of oxygen which must be consumed or depleted. For the purposes hereof desorbed oxygen will be considered to be a factor which contributes to head space oxygen. Oxygen dissolved in the plastic wall is indistinguishable from oxygen attempting to permeate through the plastic bottle walls. For the purposes hereof oxygen dissolved in the plastic bottle walls will be considered the same as oxygen attempting to permeate the bottle walls. In summary, then, beer packaged in metal cans is generally at risk only from head space oxygen. Beer in glass bottles is generally at risk from head space oxygen and also from oxygen permeation through the bottle closure means, especially crimped crown gaskets. Beer in plastic bottles is at oxygen risk from the two sources noted above and also from permeation of oxygen through the bottle wall into the bottle cavity. These considerations also apply to other products packaged in cans and bottles though the effects of oxygen can vary considerably depending on oxygen sensitivity of the product.
While the bottling of beer in plastic bottles is still in its infancy, the above recitation as methods for unwanted oxygen to be present in a plastic bottle cavity are well documented in the art, not only for bottling applications having oxygen requirements as rigorous as those for beer but also for applications less stringent than those for bottling beer. Attempts to overcome these problems for plastic bottles have often involved the use of multilayered bottles where at least one of the layers comprises a polymer (such as ethylene vinyl alcohol copolymer, EVOH) having superior passive resistance to oxygen permeation as compared to the bottling polyester which is usually polyethylene terephthalate (PET). There are disadvantages to such approaches including the following: (1) the bottles are no longer suitable for recycle with other polyester (PET) bottles because of the presence of a second and incompatible polymer (EVOH), (2) the bottles tend to delaminate at the PET/EVOH interfaces, although such delamination may be somewhat diminished (at additional expense) by the use of adhesive tie layers, (3) the differences in melting points and other physical properties between PET and EVOH cause numerous problems in the bottle fabrication-process, and (4) use of a passive oxygen barrier, such as an EVOH layer, tends to keep head space oxygen trapped within the bottle cavity instead of eliminating it.
This invention addresses these and other problems related to prior art efforts to manufacture zero and near zero oxygen permeation plastic bottles.
INVENTION SUMMARY AND PRIOR ART REVIEW
In a broad sense, therefore, this invention relates to novel bottles and a process for the production of multilayered substantially zero oxygen permeation plastic bottles. Substantially zero oxygen permeation means that the oxygen which finds it way to the bottled product is an amount which is only barely measurable with instruments which measure such permeation. In the absence of a specific amount of oxygen, substantially zero oxygen permeation will be considered to be 1 ppm of oxygen, in terms of the weight of the bottled product, for the target shelf life of the bottled product. The multilayered plastic bottles of this invention are suitable for recycle with other polyester bottles, have excellent rigidity, have good clarity when such clarity is desired, resist delamination, do not need tie layers, and also have the ability not only to keep oxygen (from air) from entering the bottle cavity but also have the ability to consume or deplete the presence of unwanted oxygen in the bottle cavity. The novel bottles of this invention involve the use of modern multilayer bottle making processes and equipment in conjunction with deployment of at least one layer (of the multilayered plastic bottle) which comprises a copolyester oxygen scavenging formulation which is an active oxygen scavenger. Active oxygen scavengers consume (or otherwise deplete) oxygen from a given environment. As noted in the co-pending application, a zero oxygen permeation multilayer bottle will have enough oxygen scavenging capacity to consume any unwanted (head space) oxygen in a bottle cavity and still have enough capacity remaining to consume oxygen at the rate at which it reaches the scavenger layer from air external to the container for the necessary shelf life of the filled bottle.
Applicants' oxygen scavenger systems are block copolycondensates comprising predominately polycondensate segments and an oxygen scavenging amount of polyolefin oligomer segments. Predominately means that at least 50 weight % of the copolycondensate may be attributed to polycondensate segments The preferred polycondensate segments, especially for bottling use are polyester segments. For layers in multilayered bottles in which some of the layers are PET or modified polyesters such as PETI, PETN, APET, PETB and/or PEN, segments of the block copolyester comprising these same polyesters are especially preferred. A primary reason is that the copolyesters most closely emulate the polyester from which its polyester segments are derived. The polyesters recited above and the various modified bottling polyesters considered safe for use with food as listed in 21 CFR § 177.1630 are the polyesters of choice for bottles because of their clarity, rigidity, and long history of usage for food and beverage storage. It will be understood that the many references to PET made in this specification shall (unless otherwise indicated) encompass not only PET, but shall also encompass PET as is commonly used in various modified forms for bottling including, but not limited, to the list of modified polyesters recited above and subsequently defined in greater detail in this specification.
The polyolefin oligomer segments are prepared for copolycondensation by first functionalizing the polyolefin oligomer segments with end groups capable of entering into polycondensation reactions. This is an important feature because the polyolefin oligomers are, in effect, addition polymers. Functionalization of the polyolefin oligomers with end groups affords a convenient method for incorporation of addition polymer segments into a copolycondensate. A pref
Cahill Paul J.
Chen Stephen Y.
Rotter George E.
BP Corporation North America Inc.
Cain Edward J.
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