Particle Fusion
Physical processes describe the transition of individual polymer particles into a continuous and solid layer during the drying of an aqueous coating. As the water evaporates, film coalescence brings the particles together until they deform and fuse into a non-porous barrier. This step is critical for developing the resistance properties of the coating.
Environmental Condition
Temperature and humidity must be carefully managed to ensure the polymer chains have enough mobility to interdiffuse. If the drying temperature is below the minimum film-forming temperature, film coalescence will be incomplete and the coating will remain powdery or cracked. This results in a failure of the barrier properties.
Coating Integrity
Successful fusion creates a surface that is resistant to water, grease, and other contaminants. The time required for this process depends on the chemical composition of the polymer and the presence of any coalescing aids. A well-fused film provides a smooth and consistent surface for printing.
If the process happens too quickly, bubbles or surface defects may be trapped within the layer. If it happens too slowly, the coating may remain tacky and cause blocking in the finished reels. This balance is essential for high-speed production lines.
Infrared drying systems are often used to trigger this phase accurately.
