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But barrier technologies lose their effectiveness at higher temperatures, which is one of the reasons that it's inadvisable to ship PET bottles over long distances.
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The first process, called Glaskin, coats the inner surface of a PET bottle with a very thin, clear layer of silicon oxide using a vacuum-deposition process. The “glass” coating reportedly can be applied at rates from 6000 to 18,000 bottles/hr. It is designed for beer, juice, and carbonated soft drinks. The coating is said to extend the shelf life of a PET bottle from four to 12 months. The silica barrier reportedly also provides excellent flavor retention.
Sealica is Tetra Pak’s patented process for molding a multi-layer PET preform using a brand-new thermoplastic epoxy barrier resin called Blox from Dow Plastics, Midland, Mich. Special equipment is used to injection mold the PET preform and then overmold it with the Blox material. This overlay process allows the thickness of the barrier to be varied as needed.
Another new process that applies silicon oxide to the outside of a PET bottle was developed by Atlanta-based Coca Cola Co. with the University of Essen, Germany. It employs vacuum-coating technology from Leybold Systems and a bottle-handling system from Krones, both in Germany. (Leybold Technologies is in Enfield, Conn., and Krones Inc. is in Franklin, Wis.).
The Barrier Enhanced Silica Treated PET (BESTPET) process reportedly gives beer a six-month shelf life. The coating process can be installed between the blowing and filling systems and can coat 0.5-liter bottles at up to 20,000/hr. The coating is also said to be 100% recyclable. A 3000-bottle/hr prototype is installed at Leybold in Germany. The first commercial unit will operate this year in a Coca-Cola bottling plant. Leybold and Krones will offer the process to other firms.
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The upcoming Nova-Pack Americas conference will hear about a “glass” barrier-coating method and an “injection overlay” technology, both developed by Tetra Pak Plastic Packaging Div. in Geneva, Switzerland, whose U.S. office is in Schaumburg, Ill. Bottles made with both techniques are said to be fully recyclable, although full-scale tests are still under way. Commercial release of the technologies will begin in this first quarter.
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Brewers generally say they need a bottle that provides shelf life of over 120 days with less than 15% loss of CO2 and admittance of no more than 1 ppm of oxygen. Internal or external coatings, and three- or five-layer PET structures using barrier materials are being evaluated to reach that performance.
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