In the dry lamination production process, whitening, fogging, and insufficient transparency are common appearance defects, often occurring in transparent films and light-colored printed films products. This problem is not related to the substrate itself; it is mainly caused by turbid
Polyurethane Adhesive systems, interface water absorption whitening, and poor film leveling. After curing, the haze increases, and the film surface becomes non-transparent, seriously affecting the appearance and texture of the product, resulting in customer returns and deductions.
Adhesive moisture absorption whitening is the core cause of whitening. Two-component polyurethane curing agents are prone to react with water vapor. When the workshop humidity is high, the ethyl acetate solvent contains excessive water, and the mixing process is left open for too long, the adhesive liquid will continuously absorb water and react, generating white flocculent insoluble substances. After coating and forming the film, the transparency of the adhesive layer decreases, and the overall appearance becomes foggy and whitish, with damaged cross-linking structure accompanied by a decrease in bonding strength.
Improper process parameters will aggravate the poor transparency. High adhesive viscosity, insufficient dilution, poor leveling, uneven thickness of the adhesive layer, and the formation of fine lines on the film surface lead to visual fogging. Low oven temperature, incomplete solvent evaporation, and residual substances in the adhesive layer cause slight turbidity. High temperature will cause the adhesive layer to quickly form a membrane, resulting in micro pores and fine lines, reducing the transparency of the film surface.
Improvement requires strict control of moisture prevention and standardization of the process from the source. Select high-purity anhydrous solvents, quickly mix the adhesive, seal it in time, and avoid adhesive liquid from absorbing moisture. Strictly control the workshop temperature and humidity, reasonably adjust the working viscosity of the adhesive to ensure uniform film leveling. Optimize the temperature gradient of the oven to ensure complete solvent evaporation without rapid membrane formation, stabilize the transparency of the adhesive layer, and completely solve the problem of whitening and fogging of the composite film, ensuring the clear and transparent appearance of the finished product.
