The composite bag is made of polyester, nylon, aluminum foil and special polyolefin and other film adhesives through a dry composite process to make a composite film, and then matured, slitted, and made into a retort bag. After the food is packaged in the composite bag, it is also subjected to high temperature sterilization at 121-135 °C for 30-40 min. Not only the film used for bag making should be resistant to high temperature, but also the adhesive used for bonding the film should also be resistant to high temperature, otherwise, the adhesion strength between films will decrease and delamination will easily occur after cooking. Now the market is mainly used for adhesives for retort bag lamination. The Research Institute of Chemical Industry has recently developed an adhesive for retort bags that is resistant to high temperature of 135°C. After several on-machine composite tests, its retort resistance, content resistance, and hygiene and safety all meet the requirements of domestic manufacturers.
        After the food is packaged in the compound folded bag, it is subjected to high temperature sterilization at 121~135 ℃ and 30~40 minutes. The packaging materials used must be resistant to high temperature. Materials commonly used in retort pouch packaging include polyester (PET), nylon (NY), aluminum foil (Al), cast polypropylene (CPP), etc. The adhesive is a two-component polyurethane adhesive that is resistant to high temperature cooking. The composite membrane is made by dry lamination process.
        The primary process of dry lamination is that the first base material is glued by the mesh roller and then enters the drying tunnel to be heated and dried by blasting, and the second base material is heated and pressed by the compound steel roller and then wound into a composite film. Then it is sent to the drying room for heating and curing for a few days, and then it is cut and bagged.