Analysis of the Low Temperature Performance of Flexible Packaging Polyurethane Adhesives

Low temperature environments are common challenges in the usage scenarios of flexible packaging. The low-temperature toughness of polyurethane adhesives directly determines whether the composite bag is less prone to cracking and delamination in cold chain storage and transportation, or in frozen packaging conditions. The adhesive layer is prone to hardening and becoming brittle at low temperatures, resulting in changes in cohesion, and subsequently leading to interface failure. This is also a key performance indicator that frozen flexible packaging needs to focus on.

 

The low-temperature performance of the adhesive is mainly determined by the molecular chain structure. A system with a high proportion of soft segments and good flexibility of the molecular chain has a lower glass transition temperature and can still maintain elasticity at low temperatures; the hard segment structure provides bonding strength, and the balance of the proportion of soft and hard segments is crucial. If the proportion of the hard segment is too high, the adhesive layer becomes more rigid at low temperatures, and is prone to cracks when bent or impacted.

The selection of the base material also affects the final effect. There are differences in the low-temperature shrinkage rates of different films, and after being compounded, internal stress is generated in the adhesive layer, which will continuously act on the interface of the adhesive layer. Even if the adhesive itself has good low-temperature performance, if the base material does not match in deformation, it will also cause a decrease in peel strength.

 

During the selection stage, for frozen packaging, polyurethane adhesives that have been developed for low-temperature adaptation should be prioritized. At the same time, complete low-temperature bending and low-temperature peel tests should be carried out. In the formulation design, the types of polyols can be adjusted to optimize the adhesive layer's resistance to low-temperature impact, while balancing the adhesion strength at normal temperatures and the low-temperature flexibility performance, to meet the long-term usage requirements of frozen food packaging.