The cooking bags used for boiling sterilization mostly adopt CPP. Due to the different product categories of CPP, their temperature resistance is also different. In this paper, the classification and application range of commonly used CPP are introduced.
(1) General purpose. Different coextrusion layers are designed for different applications. For example, it can be used for bread packaging, clothing (especially underwear, pants) packaging, fruit packaging, etc. on automatic packaging machine, or used for two-layer film with printed BOPP / CPP, used for packaging of clothing materials and dry food (such as fast food noodle bag, bowl cover, etc.). The general structure is copoly PP / Homo PP / CO PP or homopolymer.
(2) Metallized type. It is required that the surface of the product has a strong adhesion strength to the metal (such as aluminum), and can still maintain good dimensional stability and rigidity after evaporation. In addition, it has lower heat sealing temperature and higher heat sealing strength. The structure of metallized type is also copoly PP / Homo PP / CO PP.
(3) Cooking type. The two-layer copolymeric CPP used for cooking can withstand 120 ℃ and 0.15 MPa pressure cooking sterilization. It can not only keep the shape and flavor of the internal food, but also can not crack, peel or bond, and has excellent dimensional stability. It is often combined with nylon film or polyester film to package foods containing soup, meatballs, dumplings and other foods or processed frozen food before eating. The structure of cooking type three-layer PP membrane is copoly PP / CO PP / CO PP.
(4) High temperature cooking type. In order to pack roast chicken, roast spareribs, jam and beverage, a three-layer copolymeric CPP film with high temperature sterilization at 121 ~ 135 ℃ is needed for packaging. The properties of copolymerized PP are better than those of common cooking type.
In addition to the three-layer film, there are tape barrier five-layer packaging, the structure is: PP / adhesive / PA / adhesive / copolymerized PE; PP / adhesive / PA / adhesive / EVA; PP / adhesive / EVOH / adhesive / PE; PP / adhesive / EVOH / adhesive / EVA; PP / adhesive / EVOH / adhesive / PP, etc.
The CPP film used in cooking bags should be made of PP or PP particles modified by blending instead of PP. Because the CPP film made of Homo polypropylene will be crisp after high temperature cooking, the seal is easy to break during drop test, resulting in leakage of contents.
In addition, the limiting temperature of inner film adhesion is 110 ℃ for medium density polyethylene, 120 ℃ for special polyethylene, 125 ℃ for polypropylene and 140 ℃ for special polypropylene.