Polyurethane adhesives, due to their outstanding performance, are one of the most widely used and important types of adhesives in the field of flexible packaging lamination. It mainly forms a high-strength and high-toughness chemical structure through the reaction of two components (the main agent and the curing agent), thereby achieving a firm bond between films of different materials.
The following are the main types of flexible packaging applicable to polyurethane adhesives and their application structures:
1. Resistant to boiling and medium-temperature steaming packaging
This is the core application area of polyurethane adhesives, especially the heat-resistant type. This type of packaging requires the adhesive to maintain extremely strong bonding force and resistance to media even in high-temperature and high-humidity environments. Typical structures include:
(1)Transparent retort pouches: such as PET/CPP, NY/CPP, PET/NY/CPP. It is used for packaging meat, poultry, dishes, etc., and can be sterilized at 121℃ or even 135℃.
(2)Aluminum foil retort bags: such as PET/AL/CPP, NY/AL/CPP. It is used for products that require high barrier properties and longer shelf life, such as military rations, pet food, and high-end condiments.
2. High-barrier food packaging
For products that need to isolate oxygen and water vapor to maintain flavor and extend shelf life, polyurethane adhesives can effectively bond various high-barrier materials. Common structures include:
(1)Aluminum foil-containing structures: such as BOPP/AL/PE, are used for dry or easily oxidized foods like milk powder, coffee, and potato chips.
(2)Aluminum-coated film structure: such as PET/VMPET/PE, it can replace part of the aluminum foil, providing good barrier properties and being more cost-effective.
(3)Co-extruded high-barrier film structures: such as PET/EVOH/PE, are used for packaging of juices, sauces, meat products, etc., which require high oxygen barrier properties.
3. Packaging for regular food and daily chemical products
The vast majority of flexible packaging used in daily life employs general-purpose polyurethane adhesives, which have diverse structures:
(1)Light packaging: such as BOPP/VMCPP for packaging snacks and biscuits.
(2)Liquid packaging: For instance, PET/PE is used for packaging detergents, shampoos, soy sauce, vinegar, etc., and the adhesive is required to be resistant to erosion by the contents.
(3)Daily chemical packaging: such as PET/AL/PE used for laundry powder, cosmetics, etc., which requires aesthetics and barrier properties.
In the flexible packaging industry, polyurethane adhesives are almost suitable for all combinations of flexible packaging composite materials that require high strength, high durability, temperature resistance and medium resistance. Especially in harsh application scenarios involving sterilization by boiling, high barrier protection and complex content components (containing oil, acid, spiciness and solvents), it is almost an irreplaceable choice.
