Formulation and Application Key Points of Steam-Curing Grade Flexible Packaging Polyurethane Laminating Adhesive

The steaming and boiling type polyurethane laminating adhesive is a special lamination raw material for high-temperature sterilization food packaging. Relying on the high-crosslinking polyester molecular structure, it can withstand boiling and steaming processes at temperatures above 121℃, and is widely used in the lamination of packaging bags for meat marinated products, pre-prepared foods, and high-temperature sterilization snacks. 

 

This type of adhesive is made by combining high-functional polyester polyol with water-resistant curing agent. The crosslinking density is much higher than that of ordinary dry lamination adhesives. The cured adhesive layer is dense and stable, with strong ability to prevent water vapor and oil from penetrating. After steaming, it will not experience delamination, white spots, or aluminum loss, etc. For high-barrier steaming film structures such as NY/AL/CPP, PET/AL/PE, the bonding is durable and stable, and the attenuation of peel strength is extremely small. 

During the production and usage stage, there are strict process requirements. The ratio error of the two-component mixture needs to be controlled within a very narrow range. The shelf life after mixing the glue is relatively short, and it should be prepared as needed to avoid waste due to premature gelation of the glue solution. The coating amount should be moderate. If the coating is too thin, it will not be sufficient for boiling treatment. If the coating is too thick, the curing process will be slow and it is prone to residual odors. It is recommended to maintain a constant temperature and humidity in the curing environment. Only after full cross-linking can it proceed to the boiling test process. 

 

The drawback of this type of product lies in its high cost and poor adaptability to low-temperature freezing. It is only specifically used for high-temperature sterilization packaging. Currently, the industry is constantly improving and modifying the formula to balance the resistance to steaming and the low-temperature toughness, thereby expanding the application scope of integrated packaging for pre-prepared dishes and frozen cooked foods.