Polyurethane adhesives are indispensable key materials in the modern flexible packaging industry. Their outstanding comprehensive performance makes them the preferred bonding solution for composite film packaging. It creates packaging materials with multiple functions by firmly laminating different plastic films (such as BOPP, PET, PE, CPP, aluminum foil, galvanized film, etc.) together, and is widely used in many fields such as food, medicine, and daily chemicals.
1. Core advantages and performance characteristics
Polyurethane adhesives are widely used in flexible packaging, mainly due to the following outstanding advantages:
(1)Excellent bonding performance and wide adaptability: The polyurethane molecular structure contains highly polar carbamate groups, which can generate strong adhesion to the surfaces of various substrates. Whether it is polar materials (such as PET, NY), non-polar materials (such as PE, PP), or even polar aluminum foil, it can form a strong bond, solving the problem of the difficulty in laminating materials of different properties.
(2)Outstanding flexibility and durability: The cured polyurethane film has excellent flexibility and impact resistance, capable of withstanding repeated bending, rubbing and dropping during the subsequent processing of packaging bags (such as bag-making and vacuuming) and usage, avoiding delamination and cracking. At the same time, it also has excellent low-temperature resistance (frozen packaging), oil resistance and chemical resistance, which can ensure the safety and quality of the contents (especially oily foods or chemicals).
(3)Good processing performance: Currently, the mainstream is two-component solvent-based or solvent-free polyurethane adhesives. Solvent-based products have mature processes and strong applicability. Solvent-free products, on the other hand, have become a development trend due to their environmentally friendly, efficient and safe features. They are all easy to apply, have wide operating Windows, and can meet the requirements of high-speed composite production lines.
2. Specific applications in flexible packaging structures
(1)Ordinary light packaging: such as snack bags (potato chips, biscuits), usually adopts BOPP/VMCPP or BOPP/PE structure, with
Polyurethane Adhesive providing basic bonding to ensure the integrity and lightweight of the packaging.
(2)Boiling and steaming packaging: This is the high-end application field of polyurethane adhesives. Special high-temperature steam-resistant polyurethane adhesives are required. They do not degrade or peel off during high-temperature steam sterilization at 121℃ or even 135℃. They are widely used in the packaging of meat products, pickles, medical devices, etc. Their structures include PET/AL/CPP, NY/CPP, etc.
(3)High-barrier packaging: For food, medicine that needs to be preserved for a long time or products that are sensitive to oxygen and water vapor, high-barrier structures containing aluminum foil or galvanized film (such as PET/AL/PE) are often used. Polyurethane adhesives can perfectly bond these high surface energy barrier layers, ensuring there are no defects between the layers and thus maintaining the overall high barrier performance of the packaging.
(4)Stand-up Pouch: This complex packaging form is usually composed of three to four layers of materials. It requires the adhesive not only to have strong bonding properties but also extremely high flexibility to adapt to the standing shape of the bag. Polyurethane adhesive is an ideal choice.
In conclusion, polyurethane adhesives are the "soul" of flexible packaging composite materials. Their powerful bonding capacity, excellent durability and ability to meet diverse demands jointly build the technical foundation for modern flexible packaging to be safe, efficient and multi-functional, greatly promoting the development of the packaging industry. With increasingly strict environmental protection regulations, solvent-free and water-based polyurethane adhesives are enjoying broader development prospects.
