Solvent residue is a key indicator for the quality inspection of food flexible packaging, directly affecting the safety of the packaging and the odor quality. The solvent-based flexible packaging polyurethane laminating adhesive uses ethyl acetate as the diluent. If the drying and coating processes are not properly controlled, the residual solvents will remain inside the adhesive layer, causing packaging odors, contaminating the contents, and even triggering food safety inspection non-compliance issues.
The main cause of excessive solvent residue lies in the drying process. Insufficient temperature, low wind speed, and excessive film movement in the drying tunnel of the composite production line can prevent the complete evaporation of solvents in the adhesive layer. The surface adhesive liquid quickly forms a crust, sealing the internal solvents and resulting in hidden residue. At the same time, excessive coating amount and overly thick adhesive layer will significantly increase the difficulty of solvent evaporation, exacerbating the residue problem.
The ratio of glue and the quality of raw materials also affect the residual amount. Excessive addition of curing agent, unqualified purity of diluent, presence of impurities such as fusel alcohol and moisture, will reduce the efficiency of solvent evaporation and delay the drying speed of the glue layer. In addition, if the humidity in the workshop is too high and water vapor mixes into the glue layer, it will inhibit the evaporation of the solvent and aggravate the accumulation of residues.
In production control, by using methods such as staged temperature increase in the drying tunnel, matching appropriate machine speed, strictly controlling the coating dryness, and using high-purity solvents, residual substances can be effectively reduced. Additionally, during the curing stage, maintaining a constant temperature can facilitate the secondary evaporation of trace residual solvents, ensuring that the solvent residues in the finished products meet national standards and food packaging safety requirements.
