The influence of solvents on the flexible packaging polyurethane laminating adhesive

Solvents are the core auxiliary components of the flexible packaging polyurethane laminating adhesive, directly influencing the coating performance of the adhesive, the curing effect, and the quality of the composite product. They are the key factors in controlling product quality in the dry lamination process of flexible packaging. Polyurethane laminating adhesives for flexible packaging are often used in combination with inert solvents such as ethyl acetate. The purity, evaporation rate, and solubility of the solvents play a decisive role in the bonding effect. 

 

The purity of the solvent is the fundamental factor affecting the performance of the adhesive. Polyurethane curing agents are prone to undergo side reactions with water, alcohols, amines and other substances containing active hydrogen. If the moisture and alcohol impurities in the solvent exceed the standard, it will consume the curing components, resulting in incomplete curing of the adhesive, decreased bonding strength, delamination of the composite film, and residual odors. In the food packaging field, this indicator is particularly strictly required. In industrial production, it is usually required that the moisture content of ethyl acetate solvent be low to ensure the stability of the adhesive solution. 

The rate of solvent evaporation directly determines the coating and compounding quality. If the evaporation is too fast, the surface of the adhesive layer is prone to quickly form a crust, resulting in defects such as pinholes and shrinkage cavities. If the evaporation is too slow, it will cause excessive solvent residue, which not only affects the flatness of the composite film but also leads to problems such as bubble formation and reduced peel strength in the later stage. In production, different solvents are often used to regulate the evaporation rate to adapt to the production conditions. 

 

In addition, the solubility of the solvent needs to match that of the Polyurethane Resin. Insufficient solubility will result in the precipitation of the resin and the stratification of the adhesive solution, causing uneven coating. Reasonable selection and control of solvents is a crucial step in ensuring the stability, safety and service life of flexible packaging laminated products.