Analysis of the Role of Additives in Flexible Packaging Polyurethane Adhesives

Additives are indispensable components in the formulation of flexible packaging polyurethane adhesives. Although their addition proportion is not high, they can precisely regulate multiple properties of the adhesive solution and the cured film layer, meeting the requirements of different composite scenarios.

 

Flow control additives can improve the spreading ability of the adhesive solution on the film surface, eliminating apparent defects such as pinholes, stripes, and fish eyes that are prone to occur during coating. This ensures uniform thickness of the adhesive layer and maintains a flat and aesthetically pleasing surface after compounding. Defoaming additives are used to release bubbles entrained during the mixing and coating processes, preventing bubbles from remaining in the adhesive layer and avoiding problems of bubble detachment during subsequent curing and steaming stages. They are particularly important for high-speed compounding production lines.

Anti-hydrolysis additives are one of the core additives for water-resistant polyurethane adhesives. The polyurethane molecular chain is prone to hydrolysis and chain breakage under high-temperature and high-humidity conditions. Anti-hydrolysis additives can capture active groups in the system, delaying the hydrolysis process and enhancing the bonding stability of the composite film under water boiling and high-temperature steaming conditions. There are also catalytic additives that promote curing, which can adjust the reaction rate without changing the basic structure of the main adhesive, and adapt to different curing conditions while balancing production efficiency and final bonding strength.

 

The selection of additives requires careful control. Excessive addition can lead to migration, causing problems such as fogging on the composite film surface, ink fading, and contamination of the contents. In the food flexible packaging field, the selected additives must also meet relevant safety compliance requirements, taking into account performance and usage safety. In the formulation development process, it is necessary to combine the polyol system, application substrate, and end-use conditions to select suitable additive types and addition amounts, balancing processing performance, weather resistance, and hygiene indicators.