Polyurethane adhesives have become the most widely used bonding materials in the field of flexible packaging mainly due to their unique chemical structure and properties, which perfectly match the complex requirements of flexible packaging. The following are several core reasons:
1. Excellent bonding universality
Flexible packaging is usually composed of a variety of film materials with different properties, such as non-polar and low surface energy plastics like polyethylene and polypropylene, as well as aluminum foil, paper, galvanized film, etc. The molecular structure of polyurethane adhesives contains highly polar carbamate groups, and other flexible or rigid chain segments can be introduced by adjusting the formula. This designability enables it to not only form good wetting and bonding with non-polar polyolefin materials, but also generate strong intermolecular forces (such as hydrogen bonds) with polar materials (such as aluminum foil, nylon), thereby achieving the bridging role of "connecting the upper and lower", and solving the bonding problems between different materials.
2. Excellent flexibility and patience
Flexible packaging needs to be frequently bent, rubbed and even squeezed during its production and subsequent transportation, sales and use. The adhesive film formed after the curing of
Polyurethane Adhesive itself has excellent flexibility and elasticity, and can withstand these dynamic stresses without cracking or delamination. Meanwhile, it has good tolerance to oils, acids and some chemical substances, which can ensure the safety of the contents of the packaging (especially food) and prevent the packaging from delaminating due to the penetration of the contents.
3. Excellent performance adjustability
Polyurethane adhesives are classified into solvent-based, solvent-free, water-based and other types, which provides diverse options for flexible packaging production. Especially solvent-free polyurethane adhesives have become mainstream in today's increasingly strict environmental protection regulations. It cures through a 100% solid content reaction, with no solvent emissions, making it safer and more environmentally friendly, and featuring high production efficiency. Whether high heat resistance (such as steam-cooked packaging), high transparency (such as light packaging), or rapid curing is required, specific process and performance indicators can be met through precise molecular design.
4. Meet hygiene and safety standards
Polyurethane adhesives used for flexible packaging of food and medicine must comply with strict hygiene regulations. By using high-purity raw materials and mature synthetic processes, food-grade polyurethane adhesives with low odor and low migration rate can be produced, ensuring that they will not contaminate the contents of the packaging and safeguarding the health and safety of consumers.
With development, polyurethane adhesives have become an ideal choice for meeting the diverse composite and functional requirements of flexible packaging materials and complying with modern environmental protection and safety regulations, thanks to their strong bonding universality, excellent flexibility, good resistance to media, high designability and reliable safety. They are indispensable assistants for flexible packaging composite materials.
