In the plastic bottles adapted to contain carbonated beverages and the like, it is highly desirable that the bottles be formed of materials providing wall structures of low gas permeability to allow the beverages to be stored over long periods of time without substantial loss of carbonation which will cause the beverage to go "flat." It is also highly desirable that the container material be totally transparent so that the beverage stored within the container can be viewed by the consumer. In addition, it is necessary that the material forming the container or, at least the material on the inner surface of the container which is in contact with the beverage, have the approval of the United States Food and Drug Administration (FDA).
Polyethylene terepthalate (PET) is an FDA approved material which is widely used in forming plastic beverage containers. In addition, polyethylene terephthalate which has been recovered from previously used beverage containers and the like, so called recycled polyethylene terephthalate (RPET), is also used in making plastic beverage containers. While newly polymerized polyethylene terephthalate (commonly referred to as virgin PET) has, as noted above, FDA approval, recycled polyethylene terephthalate is not FDA approved and thus cannot be used next to the beverage. This has led to a practice in which beverage containers are formed of layered materials with the inner layer of virgin PET being in contact with the beverage wall and the outer layer of recycled PET being on the outside of the container. Both these various layers may be formed together by various techniques involving fusion or comolding, with or without an adhesive layer between the polyethylene terephthalate layers.
Polyethylene terephthalate is relatively permeable to carbon dioxide and oxygen so that containers formed of polyethylene terephthalate have a relatively short shelf life. In order to prolong the shelf life of such containers, it is known in the art to incorporate a barrier material into such containers. Typically, such containers may be formed of an interior layer of virgin polyethylene terephthalate, a barrier layer, and an outer layer formed of recycled polyethylene terephthalate. Containers of this nature are disclosed in U.S. Pat. No. 5,464,106 to Slat et al. As disclosed in Slat, a suitable container configuration includes an inner layer formed of polyethylene terephthalate or polyethylene naphthalate, an outer layer of recycled polyethylene terephthalate, and an intermediate barrier layer which may be formed of acrylonitrile copolymers, ethylene vinyl alcohol copolymers, vinyladene chloride copolymers, and copolymers of vinyladene chloride with vinyl chloride or methylacrylate. Various procedures are disclosed in Slat for forming the beverage containers of three layers, i.e., an interior layer of an FDA approved polymer, an intermediate barrier layer, and an outer layer such as recycled polyethylene terephthalate which does not have FDA approval. One technique involves the application of an inner layer polymer and a barrier layer polymer which are applied to an interior mold to form a preform. This can be accomplished by various techniques including coextrusion. This is followed by various procedures which can then involve an injection molding technique in which the outer layer is applied over the preform. The preform is then subjected to a blow-molding operation to arrive at the final product.
Another technique for forming beverage containers and similar multilayered articles involves so-called lamellar injection molding such as disclosed in U.S. Pat. No. 5,202,074 to Schrenk et al. As disclosed in the Schrenk patent, a plurality of thermoplastic polymers can be applied through respective extruders to a coextrusion feed block which functions to generate and arrange layers or lamella in any of a number of configurations. As described in Schrenk, using the designation of "A," "B," and "C" for three different polymers applied through extruders to a coextrusion feed block system, layer orientations of ABC, ABABA, or ABCBA configurations can be arrived at. In addition to the orientation of the various polymer materials, the thickness of individual layers or lamella can likewise be controlled, and in repetitive multiplication of the lamellar injection technique, the several polymer materials can be extruded in such thin layers that they become essentially a homogenous material. The Schrenk process discloses such lamellar injection systems in the production of plastic beverage containers involving multilayer structures incorporating an FDA-approved material such as polyethylene terephthalate with a barrier material such as ethylene vinyl alcohol.
Effective barrier materials used in the fabrication of container parisons are fusion blends of poly(ethylene terephthalate) and polyester-based copolymers as disclosed in U.S. Pat. No. 4,578,295 to Jabarin. As disclosed in Jabarin, such barrier materials include copolymers such as copolymers of terephthalic acid and isophthalic acid with one or more diols, particularly ethylene glycol in combination with other dihydroxy alcohols, specifically, 1,3 bis (2 hydroxy ethoxy) benzene. Other suitable reactants include sulfones such as bis(4-beta-hydroxy ethoxyphenol) sulfone and additives such as stabilizers, processing aids, pigments, etc. The barrier materials thus formulated can be mixed with polyethylene terephthalate to form intimate fusion blends of 80-90% PET and 10-20% polyester to form barriers that are about 20-40% better gas barriers to CO.sub.2 transmission than PET alone.
Barrier materials of the type disclosed in the Jabarin reference have heretofore been used in formulations of long shelf life beverage containers by using such materials as blends with another FDA-approved material such as polyethylene terephthalate. As disclosed in a paper by Suematsu, "Growth Prospects and Challenges for PET in Asia/Japan Producers Perspective," presented in Singapore, May 19-20, 1997, a commercially available copolyester of the type disclosed in the Jabarin patent can be blended with polyethylene terephthalate to provide a material of substantially lower permeability to carbon dioxide and polyethylene terephthalate. This product identified as copolyester B010 is said to have substantially better barrier properties than polyethylene naphalate and to be useful as a blend with polyethylene terephthalate to form a barrier material having FDA approval.