Adhesive Resins (Tie Layer Resins): Plastic packaging films are most often multilayer films that combine the properties of two or more materials. The combination of different polymer layers lowers the gas and vapour permeability, reduces cost, and improves the mechanical properties such as puncture and tear resistance. However, often dissimilar materials, when coextruded to a multilayer film, do not adhere well to each other which results in delamination and poor mechanical properties. To improve adhesion between poorly adhering layers, special adhesive polymers or tie resins are employed. Typical adhesive resins include ethylene vinyl acetate (EVA), ethylene methyl acrylate (EMA), and acid modified olefin copolymers like ethylene acrylic acid (EAA).
Adhesives for Sealing and Lamination: see Laminating adhesives
Aseptic packaging is defined as the filling of a previously sterilized product into a sterile container under aseptic conditions and hermetically sealing the container to avoid reinfection. This type of product is shelf-stable at ambient conditions.
Biaxial Oriented Film (BO) is film stretched in both machine direction and the direction transverse to it. This type of film is either produced by a blow molding process or by an extrusion cast process where the extruded or blown film is stretched in two perpendicular directions after it has been solidified. This produces a molecular chain orientation in two directions that has a significant effect on the properties of the stretched film. For example, films with biaxial orientation exhibit much increased tensile strength, improved barrier properties and greater shrinkability when compared to regular films.
Biaxially Oriented Polypropylene (BOPP) is the most important polypropylene film. It is an excellent alternative to cellophane, waxed paper, and aluminum foil. The orientation increases tensile strength and stiffness, lowers elongation (harder to stretch), and improves the vapor barrier properties.
Biaxial Oriented Nylon (BOPA) is used for a wide variety of applications especially where high gas barrier properties are required. Because of its higher price relative to PVC, PE, and PP film, it is generally considered a specialty film. It is mainly used as a flexible packaging film for food sensitive to oxygen and is chosen when high mechanical strength, high melting point, transparency, and good oxygen barrier is required. Important food packaging applications include processed meat (sausage, bacon), smoked fish, cheese and other diary products, and semi-finished microwavable meals.
Biaxially Oriented Polyester (BOPET) is the most important polyester film. In comparison to polyolefins such as PP and PE, it has better retention of physical properties over a fairly wide temperature range of about -70°C to 100°C. This type of film has found many high-volume applications that require this stronger and more dimensionally stable film. Two major drawbacks of BOPET are the higher manufacturing costs and higher capital investment in equipment.