Analysis of the Deceleration of Peel Strength of Flexible Packaging Polyurethane Adhesives

Peel strength is the most intuitive performance indicator of composite flexible packaging and is also the core basis for verifying the bonding effect of polyurethane adhesives. Such phenomena of strength deceleration may occur during the completion of the composite process, during the storage after the aging process, and during the contact with the contents.

 

The deceleration of peel strength can be classified into two types: interface type and cohesive type. Interface deceleration mostly occurs at the contact surfaces between the adhesive layer and the substrate, or between the adhesive layer and the ink. Water vapor, oils, and small molecule additives continuously invade the interface, weakening the intermolecular forces, and the obvious manifestation is that the adhesive layer does not stretch during peeling, and both sides are clean without residual adhesive. Cohesive deceleration is when the adhesive film itself is damaged, the crosslinking network is destroyed, and the peel-off can be seen as the adhesive layer breaks and the stretching is uneven. Generally, it is related to hydrolysis, medium swelling, and abnormal aging.

The formulation system is the fundamental influencing factor. An imbalance in the ratio of polyols and isocyanates will cause defects in the crosslinking network; some low-molecular-weight components migrating to the interface will also gradually weaken the bonding effect. The external environment cannot be ignored either. Long-term storage in high-temperature and high-humidity conditions will accelerate the degradation of amine carbamate bonds; continuous penetration of the internal medium will have a plasticizing and swelling effect, continuously lowering the peel-off strength.

 

Production control can delay the deceleration. Strictly controlling the mixing ratio, ensuring full curing, allowing the crosslinking reaction to proceed completely; choosing the appropriate adhesive type based on the content type, and matching the corresponding ink and substrate. At the same time, the finished product storage should avoid high-temperature and humid environments to reduce the erosion of external conditions on the composite structure, maintain stable peel-off performance, and ensure the reliability of the packaging during the shelf life.