The future is sealed

17-Nov-2004 - Last updated on 14-Mar-2017 at 08:55 GMT

With plastics soaring in price, John Dunn investigates what developments are taking place to keep costs down while meeting consumer demand for convenience

Soaring oil prices and rising demand in China are threatening to force up the price of plastics packaging in the food industry. Polyethylene terephthalate (PET) suppliers have announced a worldwide increase of over £60 a tonne. Polystyrene has risen by 60% since 2003 and polypropylene by 17%. And oil prices are also pushing up energy and transport costs.

So far, plastics packaging suppliers have largely been able to hold down prices to the food industry by absorbing costs, and by supplying thinner, lighter films, a process known as down-gauging. Other suppliers are maintaining their margins through innovation and by developing higher added-value products such as retortable resealable packaging that can be used for foods traditionally packed in cans and jars.

But it isn't just rising raw materials costs that threaten plastics suppliers' margins. Glass jars are fighting back. Rockware Glass in the UK is developing a range of microwaveable glass jars with metal lids and insulating labels that can be popped straight into the microwave to reheat the contents. All the signs are, says Rockware, that consumers prefer the look of food in glass jars to plastics packs.

"Packaging producers have long tried to do without price adaptations. At, present, however, raising prices is inevitable," claims Willi Eibner, chief executive of Greiner Packaging International, one of Europe's leading packaging suppliers.

Although raw material prices are rising, they are not totally linked to soaring oil prices, suggests David Harrison, divisional director of Supreme Flexibles, part of the UK's Supreme Plastics group. He feels polymer producers are using high oil price rises to some extent as an excuse to jack up their own prices. "Nevertheless, the oil market is in a volatile state and there are pressures on us from the food packers not to pass on prices rises." Indeed, retailers are continuing to look for price reductions, he says. "But nobody can absorb the sort of price rises we've seen in the past 18 months. Polymer prices have gone up 50%."

So the pressure is on for food packers to defray the increased costs. The most obvious way is to down-gauge using stronger polymers to reduce weight and thus cost. And the benefits are not just costs, says Harrison. Quite often a thinner, stronger film will enable packaging machinery to run faster. "That allows our customers to be more efficient," he says.

Over the past five years there has been a steady move to down-gauge, driven primarily by cost and environmental legislation aimed at reducing packaging waste. But it took off with the development of metallocene catalysed polymers which deliver thinner, stronger films. Metallocenes are organometallic compounds -- a sort of chemical sandwich of metal atoms between two layers of organic molecules. And metallocene polymerisation has revolutionised plastics packaging, particularly polyethylene and polypropylene (PP).

The reason is simple. Metallocenes produce polymers with vastly higher molecular weights than previously possible, leading to thinner, stronger films, particularly in co-extruded multi-layer laminates. "We're talking about potential reductions of 25% in gauge," says Harrison. "It's not uncommon to be able to reduce the gauge of a frozen food film, for instance, from 80 microns down to 55 microns."

And according to Amcor Flexibles, one of Europe's leading flexible packaging suppliers, ethylene vinyl alcohol (EVOH) polymer layers in extruded laminates have been down-gauged from 5-10 microns to 2 microns or less today. Another consequence is that aluminium foils used in packaging films are now half the thickness they were a few years ago -- down from 9-12 microns to nearer 6 microns.

But the problem for food packers is to ensure that these new films work on existing packaging machinery, says Harrison. "Machine trials are very important to ensure that older machines are compatible with the new films we are supplying."

The drive to reduce costs has also been accompanied by rising demand from the consumer for increased convenience in packaging, in particular resealable packaging. Although the press-and-seal zipper bag has been around for over 30 years, recent developments in retortable zippers have made resealable plastic pouches suitable for foodstuffs that were packaged in cans or jars. Developed by Supreme Plastics in conjunction with Amcor Flexibles, the retortable zipper allows food manufacturers to produce multi-portion pouches of moist foods -- everything from fish to petfood, says Supreme.

The zipper has been designed to work with viscous products and withstands distortion at temperatures up to 129°C for 45 minutes during the sterilisation process. Pouches are made from PET/oriented polyamide (OPA)/PP multi-layer polymer laminates, and can incorporate a layer of aluminium if required.

For food manufacturers, the switch from metal and glass to retortable plastic pouches reduces demand on storage space and lowers transport costs, says Supreme. Also, since heat transfer is faster through plastic, the food retains its flavour better because of the shorter cooking time.

Amcor is now promoting retortable resealable packaging following successful testing in Switzerland of trial packs made at its Denmark plant. Jonathan Fowle, group director of innovation at Amcor Flexibles says the retort zipper opens up new opportunities for consumer convenience and portion control. "On-the-go eating and foodservice applications are major target areas."

"It's a new era for us," says Shaun Toms, national sales manager for Supreme's zipper closures. "Anything that can be cooked in a can can be cooked in a retortable resealable pouch. Several customers are now doing tests and shelf-life trials."

Overall, says Toms, the use of resealable closures in food packaging has grown steadily with the increasing popularity of stand-up pouch formats which replace traditional cans, jars and cartons. But the biggest push, he says, has been provided by Supreme's development of cross-web zippers for use on vertical form, fill, and seal machines. It has developed a system that can be retrofitted to virtually any vertical form, fill, and seal machine.

In the cross-web system, short lengths of zipper are applied across the web of the polymer film entering the machine. They are placed in the middle, away from the edges, and on the same side of the web. As the pouch is formed, the zipper is in effect folded over on to itself and sealed inside the pouch, which is then filled and finally sealed.

Previous zipper systems applied the zipper in one continuous length along the edge of the film as it travelled through the packaging machine. This meant that as packs were formed, the ends of the zipper became part of the side seals of the pack, leading to the risk of leaks and potential maintenance problems with the heat sealing units.

"Cross-web zippers have now taken over almost 100%," says Toms. "They are faster and the zipper doesn't penetrate through the seal -- it doesn't affect the integrity of the pack."

Supreme is also seeing increasing demand for its slider zipper system. Unlike the press and seal zipper, a small plastic slider seals and unseals the zipper. Technology has now been developed to allow the use of the slider system on high-speed food packaging lines. And increasingly sliders can now be seen in supermarkets on resealable bags for fresh vegetables and fruit.

Supreme is also extending resealable zipper technology to continuous flow wrapping lines. According to Toms, the first applications are likely to be for flow-wrapped sliced meat -- shingled meat -- and similar products. And one or two companies in Europe are looking at producing products in trays with an overwrap that incorporates a resealable zipper, he says.

But glass jars don't need zippers, they already have resealable lids. And now research from UK glass jar maker Rockware has shown that food in glass jars can be safely heated up in a microwave, and that consumers like it.

As a result, Rockware is developing a range of insulated labels and microwaveable metal lids in order to be able to offer food manufacturers glass jars that can be put into a microwave to reheat the contents.

According to Sharon Crayton, marketing manager at Rockware Glass, Campden & Chorleywood Food Research Association (CCFRA) was asked recently to carry out microwave heating tests on 10 types of standard Rockware glass jars containing beans, pasta, and chicken soup. The results showed that there was no degradation of the glass and no cracking from thermal shock. The research also showed that shallow flat jars with a large surface area were the most suitable for microwave heating.

"When we took the microwaved food back to consumers, they loved it," says Crayton. "Glass is seen as having a no taint, clean taste. The contents look nicer, taste better, and the whole product looks more premium. Consumers have reservations about microwaving plastics."

Rockware is now working with Crown Cork and Seal to develop a microwaveable metal lid. "The idea is that the consumer would release the lid prior to microwaving. But if they don't, it will pop off anyway," says Crayton. Rockware has also developed a thin polystyrene-based label that insulates consumers' fingers from the hot glass. It will reduce the temperature felt on the fingers by about 20°C, she says. FM