The single-layer plastic film of aluminum foil bag often cannot fully meet the requirements of protecting commodities, beautifying commodities and adapting to processing. Therefore, people have developed packaging materials that are compounded with two or more layers of the same or different types of packaging materials. This composite material overcomes the shortcomings of a single material and obtains excellent properties that a single material does not have. At present, composite materials have taken the lead in food packaging.

1. The basic structure of composite materials

Generally speaking, the outer layer of the composite packaging material should be a material with a high melting point, good heat resistance, not easy to be scratched, sanded, good in printing performance, and good in optical performance. Paper, aluminum foil, cellophane, polystyrene Carbonate, nylon, polyester, polypropylene, etc.

The inner layer material should have heat-sealability, good adhesion, odorless, non-toxic, oil-resistant, water-resistant, chemical-resistant and other properties, such as polypropylene, polyethylene, polyvinylidene chloride and other heat-resistant plastic materials.

The middle layer of the composite material with more than three layers is usually made of materials with good performance and high mechanical strength such as blocking gas and moisture and shielding light, such as aluminum foil, polyvinylidene chloride, cellophane, paper, polyethylene, etc.