Aaron L. Brody

Somewhere in time, 2,000 or perhaps more years ago, beer made its way into bottles to permit this beverage to be consumed away from its brewery. Back then, the brewmasters must have used ceramic, but shortly thereafter, glass bottles, which have existed for about 5,000 years, became the structure of choice.Miller’s plastic beer bottle is made of Continental PET Technologies’ PET/MXD6/PET

Certainly, the original Budweiser, Lowenbrau, and Heineken have been packaged in glass bottles with ceramic closures since at least the 19th century. Long enough, declare the purveyors of plastic. You have already ruined our great quaff with those accursed aluminum cans, assert the traditionalists, who are supported by the resurgence of long-neck glass beer bottles during the 1990s.

Those brewers chasing the number one have attempted to differentiate themselves with a variety of strategies, not the least of which is packaging. Glass bottles shaped like baseball bats, stubbies (short glass bottles with virtually no neck), holographic labels, and wire-clinched ceramic closures are just a sampling of the alternative packages offered. But the most intriguing alternative since the 1960s has been plastic—at least from the perspective of the plastic resin suppliers, converters, and conference organizers. Who wants to remember the forays into thermoforms girdled with paper/aluminum foil, or Tetra Pak’s wonderful engineering feat called Rigello, or ICI’s unbelievable Merolite flexible sausage?

The rationale in Europe during the 1960s and ’70s was to protect referees on the field of close football (soccer to Americans) contests from pitched glass bottles. Or to reduce weight for shipping, or to prevent cuts from dropped and shattered glass bottles on swimming pool aprons or boat decks, or to, hopefully, reduce costs. Or, more recently, to reduce the shards of broken beer bottle glass resulting from football hooligans on the streets of London, Liverpool, Manchester, Frankfurt, and other European locales with fans. The Europeans take their football seriously.

The thrust toward plastic that emerged about five years ago reiterated the same reasoning, but with some new technologies that might just permit the concept to function this time—if all the marketing objectives were realized.

As most food technologists understand, beer is a fermented grain highly sensitive to oxidation and not insensitive to microbiological intrusion, carbon dioxide loss, moisture loss, light, flavor contamination, and a host of other environmental insults. Brewers like to remind us of beer’s vulnerability to all external variables, claiming the No. 1 position in sensitivity to external environmental variables such as oxygen. Whether beer is No. 1 or trying harder, it is indeed adversely affected by a host of factors which must be obviated by the integration of packaging with processing and distribution. The facts that glass can resist the temperature/time integral of pasteurization, can be colored to deter light, is inert to gas and flavor passage, can be sealed, has high vertical compressive strength, and is inexpensive all contributed to its perpetual application for beer. But, say the plastics advocates, plastic is lighter and is hardly breakable and occupies less volume for shipping, and so on. And with today’s technologies, the requisite oxygen barrier can be imparted to plastic beer bottles. If you are offered a plastic with the key oxygen barrier properties, you have cleared a major hurdle.

But today the brewmasters are being offered not just one, but a range of plastic bottles with what are claimed to be the needed gas barrier and possessing other properties necessary to contain beer. Although this topic has been discussed and dissected at many packaging events over the past two years, the subject is so complex that one wonders if any single person has a true perspective on the marriage of need to technology.

Among the very few good summaries of the field emanated one from Raj Rao and Ken Halsall of Husky, the Canadian injection molding press maker during the Bev Pak Americas 99 conference held late last year in São Paulo, Brazil. At the same conference, Norm Nieder of Anheuser Busch boldly described the needs of single-use beer packaging: shelf life of 60 days at 22°C, maximum carbon dioxide loss of less than 10%; maximum oxygen ingress of 1 ppm; pasteurization to withstand 64.4°C; and ultraviolet blockage of 15–18% at 550 nm. Those brewers who do not pasteurize beer and/or who distribute under refrigeration would alter their specifications from these typical data.

Despite the many hopes for a single monolayer plastic such as polyethylene naphthalate (PEN) or liquid crystal polymer (LCP) capable of meeting the requirements, economics must be a variable. High-gas-barrier plastics capable of being converted into monolayer bottles are simply too expensive to even consider for the present (even though some converters have commercialized PEN bottles and Anheuser Busch briefly distributed a few bottles in 1998, and Denmark’s Carlsberg offered both Carlsberg and Tuborg in 33-cL PEN bottles in late 1999). The development strategies for the proponents of both plastics has been to blend the polymers with other less-expensive structural polymers such as polyethylene terephthalate (PET), but, to date, this approach has not achieved the hoped-for results, although Coca-Cola received a 1999 DuPont packaging award for development of a shelf-life-doubling 350-mL contour bottle fabricated from a blend of Shell PET and PEN.

The direction taken by most package makers involved (and why not, since the target is tens of billions of bottles and possibly also some share of the multi-billion can market) has been multi-material plastics technology. To enhance the gas barrier, for this is the first requirement to be satisfied, multi-materials may be classified according to coinjection, overmolding, and coating. If a base polymer other than polyester were ever to be used (and polypropylene cannot be dismissed), the injection route might not be required. For now, however, polyester is the rational polymer of choice and must be injection stretch blow molded, meaning that a preform must be injection molded directly from a melt prior to blowing.

In coinjection, one means of marrying two polymers in a single structure, two or more materials are introduced into the preform mold cavity through a single gate.

In sequential coinjection, two or more materials are introduced in series into the cavity, leading to two or more layers that are subsequently blown into a multilayer bottle. The Continental PET Technologies technology for producing the Miller and Heineken plastic beer bottles requires only about 1.5% of core material, which, in this instance, is reported to be a mix of polyester with a transition metal–catalyzed polyamide oxygen scavenger. The inner layer of polyester reportedly separates the reaction products of oxygen and the scavenger from the product contents. The exterior layer reduces the burden from air on the core scavenger.

In simultaneous coinjection, two or more polymers are introduced at the same time into the injection mold cavity, leading to a multilayer structure in which a core layer may be trapped between two external layers. American National Can uses this three-layer method, based on its 1970s Omni can-fabricating technology (always remember history!) to insert about 5% ethylene vinyl alcohol (EVOH) oxygen barrier into the core layer. The polyester acts as a water vapor barrier of sorts to protect the moisture-sensitive EVOH and to reduce air entry from the exterior. In the United Kingdom, Bass Ale is using these bottles to contain its Carling Black Label, Hooper’s Hooch, Grolsch, and Kronenbourg (again, remember the past) brands.

Schmalbach Lubeca is using similar simultaneous (or sequential, depending on the objective) coinjection technology to produce preforms with core layers of 7–12% metaxylylene diamine (Mitsubishi Gas Chemical’s nylon MXD6 in trade parlance), varying the distance of the core layer from the exterior and interior polyester. These bottles have been used in France for Karlsbrau beer. Kortec hot-runner simultaneous injection molding technology implemented on Husky equipment delivers three concentric layers, including a core of a BP Amoco Amosorb oxygen scavenger tested for Bud Light beer in 1999. The exterior and interior layers were polyester.

Coating is generally performed downstream of polyester bottle blowing. During the 1970s and ’80s, the coating of choice for extending the shelf life of carbonated beverages was polyvinylidene chloride (PVDC). This system was obviated by the truncation of distribution by carbonated beverage bottlers who no longer had the need for traditional extended shelf life. PVDC is still being considered as an exterior polyester bottle gas-barrier coating.

Perhaps the most publicized coating of 1999 was Actis, the hydrogenated amorphous carbon treatment of inside surface, developed by Sidel, a French bottle molding equipment company with offices in Norcross, Ga. Acetylene is injected into the polyester bottle and ionized using microwave energy until it becomes a plasma. The molecules strike the bottle and solidify into a 1-micron-thick coating capable of reducing oxygen permeation by factor of 30.

The Japanese brewer Kirin has been developing a diamond-like interior coating using plasma-enhanced vapor deposition to enhance the oxygen barrier of polyester by one order of magnitude, or ten times.

PPG’s epoxy-amine thermoset coatings are being applied to the exterior of polyester beer bottles by Amcor for United Breweries’ Carlton’s beer in Australia. The material is sprayed on the surface after blowing, and the bottles are then infrared heated to cross polymerize and thus solidify the coating resins.

No discussion of beer bottles circa 1999/2000, regardless of how brief, can avoid mention of the Ruppman process, in which a monolayer polyester preform is heat set in the blow molding process, using cryogenic liquid instead of air to blow the bottle. The technology is reported to impart a crystallinity gradient across the plastic bottle wall, enhancing the thermal resistance and the gas barrier.

Coca-Cola Europe has reported on its BetPET system to apply (gas-barrier) silica coatings on the exterior surface by high-vacuum plasma deposition. The process is supposed to double the shelf life of carbonated beverages to six months, which could certainly be of interest to advocates of plastic beer bottles.

In its continuing departure from its traditional aseptic packaging roots, Tetra Pak has begun trials of PET bottles with silicon oxide interior coating. Their Sealica system applies a barrier resin to the exterior of preforms. The material is probably Dow Chemical’s Blox™ thermoplastic epoxy resin that adheres well to polyester and imparts gas barrier.

Japan’s Toyo Seikan has announced a heat-set pasteurizable polyester which, when combined with barrier coatings, is aimed at beer packaging.

Enough, shouts the food scientist! How does this too-wide array of technologies affect me? Of course, many food and beverage products, not just beer, require protection from oxygen in distribution channels. The barrier offered by the “traditional” EVOH and PVDC coatings on polypropylene and polyester may be sufficient—or not. This next generation suggests different routes to achieve oxygen exclusion and even removal, if need be.

If (or is it when?) barrier polyester package capacity driven by the mammoth beer bottle market is generated, the purveyors will certainly be seeking alternative markets for their outputs. But, to believe that all of the offerings are equal to—or better than—the conventional or each other would be naive. This is no longer a situation in which a food packaging technologist alone, however capable, is qualified to perform all of the requisite evaluations and render an irreversible decision. It is obvious that too many variables are involved in selecting plastic barrier structures to package oxygen-sensitive food and beverage products. The pages of this publication should be filled with results of studies on the effectiveness of those new technologies we have listed and those to come.

The following patents about packaging materials and equipment can be downloaded from www.uspto.gov by searching by keyword, patent number, or patentor, using a Boolean search on the front page of the patent section.

Biodegradable polyester and natural polymer laminates. U.S. patent 6,040,063, filed 12/15/1999, issued 3/21/2000 to W.M. Doane et al., assigned to the United States of America as represented by the Secretary of Agriculture and Biotechnology Research & Development Corp. Describes articles in which a self-supporting structure formed of natural polymer has a self-adherent, moisture-resistant hydroxy-functional polyester on the structure surface. The self-supporting structure preferably is a starch and polyvinyl alcohol blend in an expanded form. The articles typically do not delaminate even when soaked in water, and are biodegradable.

UV radiation and vapor-phase hydrogen peroxide sterilization packaging. U.S. patent 6,039,922, filed 8/15/1997, issued 3/21/2000 to R. Swank et al., assigned to Tetra Laval Holdings & Finance, SA. Describes a method and apparatus for sterilizing packaging with vapor-phase hydrogen peroxide and ultraviolet radiation on a packaging machine. A partially formed packaging material is sprayed with gaseous hydrogen peroxide, allowing the gas to condense on the packaging material. The packaging material is then conveyed to a UV radiation source for irradiation of the packaging material. The packaging material is then dried with heated air to flush/remove any residual hydrogen peroxide. The packaging material is sterilized, allowing for filling with a product such as milk, juice, or water. The packaging material may be in the form of gable-top cartons, parallelepiped containers, flexible pouches, etc. The invention allows for the efficacious use of hydrogen peroxide having a concentration of up to 53% while providing a packaging material having less than 0.5 ppm hydrogen peroxide.

Packaging unit for continuously producing sealed packages, containing pourable food products, from a tube of packaging material. U.S. patent 6,038,838, filed 5/18/1998, issued 3/21/2000 to P. Fontanazzi, assigned to Tetra Laval Holdings & Finance S.A. Describes a packaging unit for continuously producing aseptic sealed packages containing a pourable food product from a tube of packaging material filled with the food product. The unit has a first and second chain conveyor respectively having a number of jaws and a number of counter-jaws which grip the tube to heat-seal cross sections of the tube. The chain conveyors also have half-shell elements for controlling the volume of the packages. The elements are connected to respective jaws and counter-jaws and cooperate with a relative cam to control the movement of the half-shell elements to and from the supply path of the tube of packaging material.

Oxygen-scavenging filled polymer blend for food packaging applications. U.S. patent 6,037,022, filed 9/16/1997, issued 3/14/2000, to A.M. Adur et al., assigned to International Paper Co. Describes a polymer blend for coating paperboard substrate used in food packaging, particularly acidic or acid-generating foods such as fruit and vegetable juices. The blend contains an acid-activatable oxygen scavenger dispersed in a film-forming synthetic polymer such as an EVOH copolymer. When placed as a film or layer on the side of the substrate inside the container in contact with the food, the blend is effective in reducing the oxygen in the container over time to a very low concentration, replacing it with carbon dioxide.

Arrangement for an ultraviolet sterilization. U.S. patent 6,037,598, filed 1/28/1998, issued 3/14/2000 to J. Cicha, assigned to Tetra Laval Holdings & Finance, SA. Describes an arrangement for an ultraviolet sterilization system disposed on a packaging machine for processing a series of cartons. The system may have an ignitor for expediting the commencement of the UV lamp. The system may have a UV monitor for monitoring the intensity of the UV radiation directed to a series of cartons being processed on the packaging machine. The monitor will alert an operator to a change in the intensity of the UV radiation, ensuring properly sterilized cartons.

Products & Literature
ROLL STOCK for horizontal or vertical form/fill/seal machines offers extra transparency and is easily sealable. It is available in specifically designed resin formulations for use with fresh-packed products, tumble chilling, and boil-in-the-bag food products. For more information, contact C&K Manufacturing and Sales Co. LLC, 28825 Ranney Parkway, Westlake, OH 44145 (phone 800-821-7795, fax 440-871-7763, email [email protected]) —or circle 364.

BRILLIANT-CLARITY DELI CONTAINERS are made from a new amorphous polyethylene terephthlate (APET) copolyester. In at least one large chain of 82 stores, the brilliant, breakage-resistant containers were cited for increased sales and less cleanup, according to the deli director of Food City, a chain located in Kentucky, Virginia, and Tennessee. The containers have a leakproof sealing flange. The grocery chain was concerned that the containers would be too expensive, but because of the robust character, clarity, and protection afforded by the containers, they are quite competitive. For more information about APET, contact Eastman Chemical Co., P.O. Box 431, Kingsport, TN 37662-5371 (phone 423-229-2881, fax 423-229-8595)—or circle 365. For information about the containers, contact Genpak Corp., P.O. Box 431, Glens Falls, NY 12801 (phone 518-798-9511, fax 518-798-1730)—or circle 366.

BREATHABLE BARRIER FILM doesn’t fog, thanks to an anti-fog system within the inner layers of the film structure. The placement of the system assures long-term effectiveness, and the antifog feature can be extended to the outer edges of the film, unlike systems applied to the surface of films. The film can be used in easy-open packages as well, with peel/reseal features and directional tear strips. Useful in packaging for fresh-cut produce, the FreshFlex film can be heat sealed without interference from the anti-fog system. For more information, contact Curwood, Inc., 2200 Badger Ave., Oshkosh, WI 54903 (phone 800-544-4672, fax 920-30307306, www.curwood.com) —or circle 367.

Contributing Editor