Coinjection, overmolding, barrier coatings, resin blends--all are being tested in the race to capture a swig of the mega-market for beer bottles.
It appears that no one plastic can satisfy every requirement for a U.S. beer bottle--at least not without help. Many approaches are being explored with multi-layer structures, polymer blends, coatings, and oxygen scavengers (see also p. 39.)
Five or so years ago, monolayer PET beer bottles were tested in the market, but they did not succeed. "It has to perform like a glass bottle," says Roman F. Barski Jr., development manager at Chicago-based BP Amoco. That means limiting oxygen permeation to 1 ppm, and carbonation loss to 15%, over 120 days. Meeting that challenge requires two to five times the barrier performance of PET.
The bottle may also have to survive pasteurization temperatures around 172 F for 15 min, which reportedly also exceeds the capabilities of PET.
A plastic single-serve beer bottle that can meet all these and other challenges--including cost and recyclability--has a chance to grab at least a 1% stake in the domestic market, which translates into about 640 million bottles annually.
Lots of choices
"By itself, a PET bottle has a shelf life of nine days before it reaches the oxygen permeation limit," says BP Amoco's Barski. Some sources expect to see higher-barrier PET resins in the next year. For now, a number of other barrier materials are being evaluated.
There are also many ways of incorporating the barrier into a PET bottle. Multi-layer preforms can be produced by coinjection or two-step overmolding. Or, the barrier material can be blended with the PET in a monolayer structure. Coatings of epoxy amine, silicon oxide, or PVDC can be applied after the bottle is blown. These different approaches may have different implications for cost and recyclability.
A number of papers presented at the Nova-Pack Americas '99 conference in February, sponsored by Schotland Business Research, Skillman, N.J., summarized recent developments in barrier technology for beer bottles. Eval Co. reported on two new EVOH materials that provide 50-100 times the barrier of plain PET. Eval XEP-438 and XEP-439 reportedly have a better oxygen barrier than nylon or PEN. Delamination resistance of EVOH/PET is reportedly better as well. The EVOH costs about $2.65/lb. By the end of the year, Eval Co. plans to release an EVOH with oxygen-scavenging capability.
PEN beats the heat
Shell Chemical produced a test bottle made from a blend of 10% of its Hipertuf 89010 PEN resin and 90% PET. Shell also showed a bottle of 100% PEN. Despite the high resin cost, the all-PEN bottle has the advantage of adequate heat resistance to withstand high-temperature pasteurization. Though its gas barrier is four to five times higher than that of PET, PEN may not provide enough long-term barrier, says Continental's Hassan. Sources at Eastman Chemical, another PEN producer, also doubt that PEN alone will suffice.
PET & MXD6 nylon
MXD6 nylon can provide 19-20 times higher barrier than PET, says Ken Halsall, business manager of preform systems for Husky. MXD6 has a processing temperature similar to PET. Halsall points out that there are some unanswered questions of how MXD6 affects crystallinity, orientation, and sensitivity to moisture and heat.
MXD6 is being used in a few market tests, according to Hiroyuki Otsuka, manager of petrochemicals for Mitsubishi Gas Chemical America, which supplies the resin. He says 30% MXD6 can be blended with PET, but the drawback is higher haze. Sources at Krupp Corpoplast say work is being done with multilayer bottles of PET and a blend of LCP and MXD6.
Coating is a first
PPG Industries offers an epoxy amine barrier coating, trade-named Bairocade, which is sprayed onto the bottle. According to senior research associate Leland Carblom, this coating is less sensitive to temperature and humidity than many barrier resins. Also, it can be removed with a caustic bath containing surfactants. The clear coating amounts to less than 1% by weight of the finished container, but it gives a clear PET beer bottle a shelf life of three to six months or more, according to PPG. This coating is used in the world's first commercial single-serve beer bottle, made in Australia.
Superex Polymer Inc., Waltham, Mass., has produced a 400-cc bottle from a PET/LCP alloy. Oxygen permeability was reduced roughly 70% with the addition of 4.5% LCP, says president Rick Lusignea. LCP has over 200 times greater oxygen barrier than PET, is not affected by moisture or high humidity, and can be used in small quantities. Good adhesion between the two materials eliminates need for a tie layer. However, LCP is opaque, and the LCP/PET preform is difficult to stretch-blow mold because of the different forming conditions of the materials, Lusignea concedes.
Undeterred, Superex is developing a transparent LCP for potential bottle uses. LCP also could raise concerns about recyclability, though that may depend on the amount of LCP used in the bottle.
Nanocomposites bow in
Nanocor Inc. and Eastman Chemical Co. announced at the conference a joint development effort in PET/clay nanocomposites. This approach has already been demonstrated to produce higher barrier without affecting clarity in nylon 6 films. The nanometer-size clay particles make an obstacle course for any gas molecules penetrating the bottle wall. The nano-clay particles are also too small to interfere with light transmission. The clay may increase melt strength and bottle stiffness.
Scavengers suck up oxygen
Amoco Polymers, part of BP Amoco Chemicals, recently introduced an oxygen-scavenging copolyester resin called Amosorb 3000. The company also offers an Amosorb oxygen-scavenging additive. These materials have the advantage of removing oxygen already present in the fluid contents or headspace. Test-market programs by both Miller Brewing Co., Milwaukee, and Heineken of the Netherlands utilize the scavenger approach. In addition, just last month, Anheuser Busch, Milwaukee, began test marketing Budweiser and Bud Lite beers in a multi-layer amber PET bottle incorporating Amosorb 3000. The bottle is made by Twinpak Inc., Mississauga, Ont.