Aluminum Foils and Metallized Films

Aluminum foil (between 0.0003 and 0.0015 in thick) is used in such food-packaging applications as pouches and liddings. The foil is usually laminated to one or more layers of plastic or paper. An example is the military meal-ready-to-eat pouch that uses a laminated structure of PET/ adhesive/aluminum/adhesive/polypropylene, from outside to inside. The aluminum foil layer provides an excellent barrier to moisture and gases, unless pinholes exist.

The metallized film consists of a very thin layer of aluminum (compared to the foil) that is vapor deposited onto the surface of a plastic film, such as polyester or nylon. The aluminum improves the gas- and light-barrier properties of the film as well as its aesthetic appeal. However, the gas-barrier properties of the metallized film are easily reduced due to handling that results in the formation of pinholes. The metallized film is used in such applications as bags for potato chips or snacks. It can also be laminated to paperboard for such applications as liquid-box juice containers.

Susceptor is a special type of metallized film used in microwavable food packages (1). A typical susceptor is a laminate consisting of the structure PET/adhesive/alumi-num/adhesive/paperboard. The aluminum in the laminate is a very thin, discontinuous layer of aluminum particles that can convert microwave energy into heat, causing the temperature of the susceptor to rise above 200°C rapidly. The high temperature is important for applications such as microwavable popcorn and pizza. However, the high temperature also raises safety concerns about thermal degradation of the PET and the migration of undesirable compounds from the susceptor to the food.

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