Most of the retort pouches used for boiling sterilization use CPP. Due to the different product categories of CPP, the temperature resistance is also different. Here, the classification and application range of common CPP are introduced.
(1) Universal type. Multi-layer co-extruded cast films are designed for different coextrusion levels for different applications. For example, it is used for bread packaging, clothing (especially underwear, pants) packaging, fruit packaging, etc. on automatic packaging machines, or for BOPP/CPP two-layer film after printing, for clothing, dry food (such as fast food noodle bags, Bowl cover, etc.) packaging. The general-purpose structure is copolymerized PP/homopoly PP/copolymerized PP or homopolymerized.
(2) Metallization type. The surface of the product is required to have a strong adhesion strength to the vapor-deposited metal (such as aluminum), and still maintain good dimensional stability and rigidity after vapor deposition. In addition, it has a lower heat sealing temperature and a higher heat seal strength. The metallized structure is also a copolymerized PP/homopoly PP/copolymerized PP.
(3) Cooking type. The two-layer copolymerized CPP for cooking can withstand retort sterilization at a pressure of 120 ° C and 0.15 MPa. It not only maintains the shape and flavor of the internal food, but also does not crack, peel or bond the film, and has excellent dimensional stability. It is often compounded with a nylon film or a polyester film, and contains a soup-like food as well as meatballs and dumplings. Wait for food or pre-food frozen food. The retort type three-layer PP film structure is copolymerized PP/copolymerized PP/copolymerized PP.
(4) High temperature cooking type. Packed roast chicken, ribs and jam, beverage, three-layer copolymerized CPP film with high temperature sterilization at 121~135 °C. The copolymerized PP requires better performance than the general cooking type PP.
In addition to the three-layer film, there are five layers of cast barrier, the structure is: PP / adhesive / PA / adhesive / copolymerized PE; PP / adhesive / PA / adhesive / EVA; PP / adhesive / EVOH / binder / PE; PP / binder / EVOH / binder / EVA; PP / binder / EVOH / binder / PP.
The CPP film used in the retort pouch should be made of copolypropylene or blended modified polypropylene pellets instead of homopolypropylene. Since the CPP film made of homopolypropylene is chopped after being cooked at a high temperature, the seal is easily broken during the drop test, causing leakage of contents.
In addition, the limit temperature of the inner film adhesion is 110 ° C for medium density polyethylene, 120 ° C for special polyethylene, 125 ° C for polypropylene, and 140 ° C for special polypropylene.