Polyurethane adhesives are indispensable key materials in the modern flexible packaging industry, and their performance directly determines the quality, safety and functionality of packaging bags. Its role in flexible packaging is mainly reflected in the following aspects:
1. Achieve multi-layer compounding to build high-performance barriers
The core advantage of flexible packaging lies in integrating multiple properties by laminating films of different materials (such as polyethylene (PE), polypropylene (BOPP), polyester (BOPET), aluminum foil, galvanized film, etc.) together. Polyurethane adhesives play the role of a "bridge" in this process. It can firmly bond these materials with distinct properties and different surface energies together to form a complete composite structure.
This composite structure achieves an effect of "1+1>2". For instance, by combining aluminum foil or nylon with excellent barrier properties and polyethylene with good heat-sealing performance, the former ensures the packaging's strong barrier against oxygen and water vapor, thereby extending the shelf life of food. The latter provides reliable heat-sealing edges, facilitating bag making and sealing. The adhesive layer formed by the
Polyurethane Adhesive itself also has certain barrier properties, further enhancing the protective performance of the overall packaging.
2. Excellent comprehensive performance meets strict requirements
Polyurethane adhesives have become mainstream due to their outstanding comprehensive performance:
(1)High bonding strength and durability: It can form a tough bonding layer, endowing the composite film with excellent peel strength. This means that the packaging bags can withstand various mechanical stresses and frictions during subsequent processing (such as bag-making and printing), transportation, storage, and even consumer use, avoiding problems such as delamination and bubbling, and ensuring the integrity of the packaging.
(2)Good flexibility and impact resistance: Flexible packaging needs to be frequently squeezed and bent. The film formed after the curing of polyurethane adhesive itself has excellent flexibility and can deform synchronously with the plastic film without becoming brittle or cracking. This is crucial for packaging puffed foods, liquid contents or foods that need to be frozen, as it can effectively resist the impact of the contents and low-temperature environments.
(3)Heat resistance: Many soft-packaged foods need to undergo high-temperature steaming (such as 121℃) or boiling sterilization treatment. Polyurethane adhesives, especially the specially developed cooked grade products, can maintain stable bonding performance in such high-temperature and high-humidity environments without degradation or delamination, ensuring food safety and a long shelf life.
3. Adapt to high-speed automated production
Modern flexible packaging production emphasizes high efficiency. Polyurethane adhesives (mainly two-component solvent-based or solvent-free types) have good operational adaptability. They have an appropriate initial viscosity, good leveling property, and are easy to be evenly coated on high-speed dry laminating machines or solvent-free laminating machines, perfectly matching the production line speed. An appropriate open time ensures operational feasibility, while a controllable curing speed guarantees production efficiency. Solvent-free polyurethane adhesives are even more in line with the environmental protection trend, with almost no VOCs emissions, and offer better production safety and environmental friendliness.
4. A Crucial Link in Ensuring food Safety
The safety of adhesives is of vital importance for packaging that comes into direct contact with food. Polyurethane adhesives that meet regulatory requirements have a stable chemical structure, use pure raw materials, and have low monomer residue. After curing is completed, it becomes an inert high-molecular polymer by itself, which will not migrate harmful substances into food and will not affect the flavor and odor of food (anti-odor property), thus providing an important guarantee for food safety.
Summary
Polyurethane adhesives in flexible packaging are far more than just simple "glue". It serves as the design foundation and manufacturing cornerstone for achieving high-performance composite packaging structures. By providing strong, durable and safe bonding, it endows flexible packaging with powerful protective functions, convenient performance and a wide range of applications. From ordinary snack bags to high-demand pharmaceutical packaging and high-temperature cooking bags, the outstanding contribution of polyurethane adhesives is indispensable behind all these.
