Polypropylene PP is a plastic formed by polymerization of propylene monomers.
There are two methods for manufacturing polypropylene film used in packaging, one is the casting method for producing polypropylene film (CPP), and the other is the biaxial stretching method for producing polypropylene thin film (BOPP). Cast polypropylene is a thin film of polypropylene extruded through a die using an extruder, which is immediately cooled into a film by a cooling roller. The main method is to manufacture high-temperature resistant (above 121 ℃) and vacuum aluminum plated films with heat sealing properties, mainly based on copolymerized polypropylene pellets. Biaxially stretched polypropylene is a process of extruding pure polypropylene into thin sheets, then stretching longitudinally and horizontally at a certain temperature, followed by heat setting and cooling to form a film.
Due to the different processing methods, the resulting product performance is also different. BOPP film has excellent transparency, heat resistance, and barrier properties compared to CPP film. It is widely used in the outer layer of composite bags, and when combined with LDPE, EVA, EEA, EAA or aluminum foil, polyolefin woven bag cloth, etc. with good heat sealing properties, it greatly improves the rigidity, stiffness, and physical and mechanical properties of the composite film. If PVDC with excellent moisture resistance and barrier properties is applied to the BOPP base film, it can not only give it a certain degree of heat sealing, but also greatly improve its impermeability. It is widely used in cigarette packaging and magnetic tape packaging.
CPP is commonly used in the inner layer of composite packaging due to its good heat sealing properties, especially in high-temperature resistant (above 121 ℃) cooking bags, which is essential. It can also manufacture cooking bags that are resistant to high temperatures of 145 ℃ and can be sterilized for a short period of time. In addition, CPP vacuum aluminum plating is then combined with BOPP, PET, OPA, PT and other composite materials, which are also used as inner layer materials in many occasions.
