PET bottle makers learned about two developmental exterior coatings that provide both barrier and bottle-decoration options at the recent Nova-Pack Americas 2000 Conference in Orlando, Fla. Other highlights of the meeting included two new barrier technologies for multi-layer preforms and two new tooling advances.
Barrier plus good looks
Add a barrier, then add holographic imaging, printed decoration, or color to your PET bottle with a new two-stage coating process in development from DuPont Polyester, Wilmington, Del. DuPont first coats the outside of the bottle with a proprietary water-releasable coating. Decorative and functional effects--such as gas barrier or uv protection--may be incorporated in the first or second coating layer (DuPont declines to be specific). The key point is that since the base coat is water releasable, anything put on top of it can be removed as well.
DuPont says its barrier coating provides 30-fold improvement in oxygen and CO2 barrier--sufficient for six-month shelf life of a single-serve beer bottle. Preliminary testing shows that coated bottles can be recycled through a conventional PET flake washing process, says market-development manager Susan Procaccini. No further details were available.
Meanwhile, a new waterborne coating that adds color, gloss, and special effects to PET containers without affecting recyclability is in development at ICI Packaging Coatings, Strongsville, Ohio. ICI's tests indicate that flow coating is the best way to apply the bottle coating, which can be transparent blue, green, or amber, as well as pearlescent white. Custom colors are also possible. The coating is cured for 90 sec at 140-158 F. A 2-liter bottle requires only 400 mg of coating. The process reportedly runs at standard line speeds with minimal VOC emissions.
ICI so far has applied the coating only to the body of a bottle, not the neck or thread. In addition, a study revealed some problems with incomplete colorant removal in recycling, which could limit reclaimed material to non-critical appearance uses or else require blending with uncolored PET before reuse. ICI hopes that high enough levels of colorant removal will be achieved to allow for direct bottle-to-bottle recycling.
New barrier resins
Imperm is a new nylon nanocomposite barrier material developed by Eastman Chemical Co., Kingsport, Tenn., in cooperation with nanoclay producer Nanocor of Arlington Heights, Ill. Imperm will become commercially available in June. Designed for use in multi-layer bottles, the nanocomposite is said to provide 50-100 times greater oxygen barrier than PET. In comparison, MXD6 barrier nylon provides 10-20 times barrier improvement over PET. Eastman plans to offer Imperm pellets for initial applications in beer and carbonated soft drinks. Eastman is developing an amber nanocomposite that incorporates uv protection as well as an oxygen scavenger.
Eastman tested a 29-g, three-layer PET/Imperm/PET bottle with the barrier layer constituting first 4% then 10% of the bottle wall. The bottle with 4% Imperm had three to five times greater oxygen barrier than PET and less than 8% haze. The bottle with 10% Imperm had six- to 11-fold barrier improvement and less than 15% haze. Imperm resin reportedly processes much like PET.
There's also news in EVOH barrier resins: A "third-generation" delamination-resistant EVOH was presented at Nova-Pack by Eval Co. of America (Evalca), Pasadena, Texas. Experimental Eval grade XEP-567 reportedly beats previous EVOH grades, as well as MXD6 and other nylons, in its adhesion to PET without a tie layer. What's more, its oxygen permeability is about 50% lower and CO2 permeation about 40% lower than those of Eval XEP-562, a second-generation delamination-resistant resin introduced last year. Eval XEP-562 is currently used domestically in ketchup bottles. New XEP-567 has only slightly greater gas permeation than conventional EVOH (32% ethylene).
XEP-567 was developed with Ball Corp. of Atlanta and its first commercial application is a plastic beer bottle for Dixie Brewing Co., Nashville, Tenn. The new material reportedly offers a shelf life of 16 weeks to carbonated soft drinks. Although XEP-567 is intended to eliminate the need for a tie layer, it readily separates from PET in standard recycling systems, where up to 85% removal can be achieved, Evalca says. The company is working on methods to boost EVOH removal to 95% or even 99.75%.
Preform tooling advances
Improved preform mold cooling could cut cycle times by as much as 2 sec and improve quality, says Rowland Frank Evans, managing director of REPS Ltd. in the U.K. (represented by Injection Molding Industries, Orion, Mich.). REPS developed its pulse-cooling method 11 years ago. Up to now, it has been used widely in injection molding, but not yet for PET preforms.
Pulsed cooling is an on/off method that pulses a rapid flow of water through the mold at the start of the cycle and then stops the flow at a predetermined point. As compared with normal continuous coolant flow, Evans says pulsed cooling achieves better heat removal without overcooling. The mold is allowed warm up before the next cycle. The result is reportedly less mold sweat, reduced stringing and crystallinity of the PET at the gate, and as much as 90% reduction in water consumption, permitting use of a much smaller chiller.
Boosting performance of smaller PET bottles (under 20 oz) for hot-fill or heat-set applications such as juices, ready-to-drink teas, or carbonated soft drinks is the initial target of new multi-layer PET preform technology in development at Kortec Inc., Beverly, Mass. Kortec is developing coinjection PET preform tooling capable of making four-layer, three-material preforms--one more layer and material than are found in the vast majority of coinjected PET containers. (A few beer bottles have had five layers.) Paul Swenson, president of Kortec, says the higher surface-to-volume ratio raises barrier performance requirements at smaller bottle sizes.
The four-layer structure uses a layer of virgin PET for the skins of the preform, which constitute 65% of total preform volume. The middle layer consists of a barrier and either an oxygen scavenger or, for cost savings, a layer of recycled PET. The PET skins are injected first, followed simultaneously by injection of the two middle layers. Swenson says the four-layer tooling technology will operate at cycle times that match monolayer PET preform production. He expects to have a prototype four-cavity unit ready this summer, and commercial rollout is planned for 2001.