日期：2022/2/23 8:47:35 / 閱讀： / 來源：本站
Polypropylene (PP) is a plastic polymerized from propylene monomers.
The polypropylene film used in packaging can be produced by two methods, one is the polypropylene film (CPP) produced by the casting method, and the other is the polypropylene thin film (BOPP) produced by the biaxial stretching method. Casting polypropylene is to use an extruder to extrude polypropylene through a die to cool the sheet immediately through a cooling roll to form a film. It is mainly based on copolymerized polypropylene pellets to manufacture heat-sealable high-temperature (above 121°C) retort-resistant films and vacuum aluminized films. Biaxially oriented polypropylene is to extrude pure polypropylene into thin sheets first, then stretch longitudinally and transversely at a certain temperature, heat-set and then cool to form a film.
Because the two processing methods are different, the properties of the obtained products are also different. BOPP film has very good transparency, better heat resistance than CPP film, and better barrier properties. It is widely used in the outer layer of composite bags. It is combined with LDPE, EVA, EEA, The combination of EAA or aluminum foil, polyolefin woven bag cloth, etc., greatly improves the rigidity, stiffness and physical and mechanical properties of the composite film. If the BOPP base film is coated with PVDC with excellent moisture barrier properties, it can not only have a certain heat sealability, but also greatly improve its permeability resistance. It is widely used in cigarette packaging and tape packaging.
Because of its good heat-sealability, CPP is mostly used in the inner layer of composite packaging, especially for high temperature resistant (above 121°C) retort bags. It can also manufacture retort bags that are resistant to 145°C high temperature and short time sterilization. In addition, CPP is vacuum-plated and then compounded with BOPP, PET, OPA, PT, etc., and is used as an inner layer material in many occasions.
In addition to BOPP and CPP polypropylene films, there is also a down-blown water-cooling method to manufacture high-transparency polypropylene films. This polypropylene film has good transparency like BOPP and good heat-sealability, and is mostly used in single-film garments.