Plastics are becoming increasingly popular as packaging materials for processed meals and pre-packaged fresh and cooked meat. At K 2004 the sector was well represented with new and innovative materials and technologies that make packaged food safer, more interesting and quick to serve. German manufacturers were at the forefront.

In addition to aluminium and cardboard, convenience foods are frequently packaged in vacuum-formed plastic trays. According to the German association for packaging market research, Gesellschaft für Verpackungsmarktforschung (GVM, D-65203 Wiesbaden, www.gvm-wiesbaden.de), consumption of thermoformed trays in Germany has jumped by 45% in the five years from 1998 to 2003, from 4.06 bn units to 5.92 bn.

Packing and filling companies either turn to ready-made trays or manufacture them in a form-fill-seal (FFS) process., but 90% of trays for instant meals and snack foods are produced off-premises, says Roland Schultz of RPC Bebo Plastik (D-27432 Bremervörde; www.rpc-bebo.nl). This is because the process is often difficult. Trays with multiple cavities or complex vacuum-formed geometries are especially demanding. Schultz explains that if the plastic fails to spread evenly during the vacuum forming process, heating the packaging during pasteurisation, sterilisation or preparation can cause it to deform.

As well as CPET trays, fresh, on-the-spot meals and refrigerated snacks are packaged mainly in multi-layer PP containers with an ethylene vinyl alcohol (EVOH) barrier film. “It´s not unusual for convenience food trays to comprise three to six layers,” explains Ulrich Kremer of Silver Plastics (D-53840 Troisdorf; www.silverplastics.de), a manufacturer of foamed PS and PP packaging. The company manufactures up to 15,000 t/y of vacuum-formed films annually at seven extrusion plants. Two of these, co-extrusion plants from German machinery manufacturer Reifenhäuser (D-53839 Troisdorf; www.reifenhauser.com), can produce up to 3m packages daily.

Lidding films with special features
Many lidding films now include features such as anti-fogging, while multi-layered structures provide improved barrier properties. Other considerations are seal, strength, printability and transparency.

“NeoSteam” from Frantschach / Neoplex (A-1030 Vienna; www.frantschach.com) is a two-layer composite film with an integrated valve system which lends itself to flexographic printing and is also available as a lidding film.

Another variation is a disposable microwave cooking pot incorporating a valve. Huhtamäki´s (FIN-02100 Espoo; www.huhtamaki.com) “Steam Chef” system (PP or CPET bowls) also cooks using steam, without the need for piercing or removing the lidding film.

Special films also allow food to be browned and baked. “Ecovent”, from Südpack (D-88412 Ochsenhausen; www.suedpack.com), is a baking foil adapted to microwave use for ready-made meals and fast foods packaged in modified atmosphere packaging (MAP). Again, the packaging acts as a pressure cooker but the packaging opens automatically when pressure builds up. The transparent composite film also lends itself to printing with as many as 12 colours in intaglio printing and up to 10 in flexography.

Resealable packaging guarantees freshness
Meat is increasingly pre-packaged and in addition to PP (as a single layer), other materials commonly used to package meats are PET, expanded PP and EPS.

“Multipeel”, from Südpack, is a resealable packaging manufactured from barrier films. The company claims that its multi-layer PET-based composite film, which features an “adjustable oxygen barrier,” can be processed on all current vacuum-forming packaging machines. Another composite film, “Reseal-it”, can be used as either a lidding film over a rigid tray or as a tubular bag – both with a resealable adhesive label.

According to Südpack, its resealable “snap-on lid”, moulded from rigid film, is particularly suitable for packaging of sliced meats and sausages that are removed from the pack slice-by-slice. Additionally, intaglio printing between layers of film prevents odours from penetrating the package contents. A metalised PS / PET composite is used for the tray, while the lidding film is an APET / PE mixture.

While most manufacturers want to stop flavour migrating, “Sun Smoke” products developed by World Pac International (FL-9486 Schaanwald; www.worldpac.li) are multi- layer (PE / PA / PE) sausage wrappers that have been impregnated with liquid smoked flavourings. When boiled sausages, corned meat or poultry products are packaged in the films the flavour transfers to the contents removing the need for the otherwise lengthy smoking process.