The influence of air humidity on the polyurethane laminating adhesive for flexible packaging

The flexible packaging polyurethane laminating adhesive is highly sensitive to air humidity. Humidity is the core environmental factor that affects its curing reaction, bonding strength and product quality. It directly determines the construction effect and bonding stability. In industrial construction, it is necessary to strictly control the environmental humidity. 

 

The appropriate humidity is the optimal environment for the curing of polyurethane adhesives. Adequate moisture can assist in the cross-linking and curing of single-component polyurethane adhesives, ensuring a uniform reaction of the glue, forming a dense and uniform adhesive layer, fully exerting the high-strength and high-toughness bonding performance, and without causing quality defects. This is the standard humidity condition for industrial bonding construction. 

Excessive humidity can seriously compromise the bonding quality. When the environmental humidity exceeds 75%, water molecules in the air will preferentially react with the isocyanate curing agent in the adhesive, significantly consuming the effective components and hindering the normal cross-linking of the main agent and the curing agent. At the same time, this reaction will generate carbon dioxide gas, causing bubbles, white spots, and pores in the adhesive layer, resulting in a loose and brittle adhesive layer, a significant decrease in bonding strength, and a high likelihood of problems such as substrate delamination and peeling. It will also cause excessive solvent residue. 

 

When the humidity is too low, the lack of water vapor will cause the curing rate of the single-component Polyurethane Adhesive to significantly slow down, and even result in incomplete curing and surface drying while the interior remains un-dried. This will prolong the construction period and reduce the bonding strength. Therefore, during the application of polyurethane adhesive, it is necessary to strictly control the temperature and humidity to avoid quality risks caused by abnormal humidity.