The most commonly used polymers coatings for plastic film manufacturing are plastisol, latex, neoprene, polyurethane, and epoxy. Cellulosics, such as cellulose nitrate lacquers, are also used to provide an unsurpassed shine and ease of retouching. Plasticizers are added to lower processing temperatures and improve the performance of the plastic film in terms of impact resistance, flexibility, crack resistance, and stability to light and heat. Plastic films are widely used for packaging, protective films, stickers, stamps, labels, and other graphic applications.
The most popular types of plastic films are low density polyethylene (LDPE), polypropylene (PP), bioriented polypropylene (BOPP), and polyester (PET). Aluminized films like aluminized polyester film (VMPET) and aluminized CPP film (VMCPP) are also used. Polyester film is made from polyethylene terephthalate as a raw material. It is extruded into a thick sheet and then stretched biaxially.
Polyethylene glycol (PEG) with lower molecular grades (200-600) is often used as a plasticizer in coating aqueous films. PVA coated high barrier film is manufactured by coating PVA with nanoinorganic substances added to a polyethylene film to increase its profitability. Hydroxyethylcellulose (HEC) is usually combined with a primary film coating polymer such as HPMC to improve adhesion to the substrate and enhance the flexibility of the film. This class of polymer is widely used in pharmaceutical dosage forms for film coatings due to its common use since the early days of film coating when organic solvents were always used; its global regulatory acceptance; its ease of availability from various suppliers; and its ability to form coatings that generally have acceptable properties.
The aluminum coating on the surface of the film serves to shade and prevent ultraviolet radiation, which extends the life of the contents and improves the brightness of the film. Immediate release film coating (also known as “non-functional” film coating or conventional film coating) is used to improve the appearance of the product, handling, and stability of the dosage form without affecting its biopharmaceutical properties. Aluminized films have both plastic and metal characteristics. Low-density polyethylene films are soft, shiny, translucent films with excellent chemical stability, heat sealability, water and moisture resistance, frost resistance, and can be boiled.
The main disadvantage of biaxially oriented polypropylene films is their poor heat sealing capacity; thus they are usually used as an outer layer in composite films. Molten polypropylene films are produced by a casting process and can be divided into normal CPP and CPP suitable for cooking. Polyethylene terephthalate (PET) or oriented polypropylene (OPP) plastics (gas barrier) as well as metallic films (aroma protection) can be coated.
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