Polymer Solution
Organic solvent solutions of polyurethane polymers deposit high-performance protective films on paperboard and film substrates through solvent evaporation and crosslinking. Applied in specialized lamination and barrier coating processes, solventborne polyurethane provides rapid drying speeds and superior chemical resistance compared to waterborne alternatives. The carrier solvent wets low-energy surfaces effectively, allowing complete wetting of synthetic films and dense paperboard grades.
Fully reacted polyurethane chains or two-component reactive prepolymers form tough, flexible topcoats upon drying. The hydrophobic nature of the polyurethane backbone prevents moisture penetration and maintains bond strength in humid environments.
Coating Flow
High-speed rotogravure and roll coating equipment rely on precise viscosity control of the liquid coating to maintain uniform film weight. Solventborne polyurethane formulations exhibit low surface tension, enabling smooth laydown without pinholes on porous paperboard. Rapid solvent evaporation in flotation dryers locks the coating in place before deep penetration into the paperboard substrate occurs.
Environmental and safety regulations require closed-loop solvent recovery or thermal oxidizer systems to capture volatile organic compounds emitted during drying. Inadequate drying leaves residual solvent in the coating, causing odor retention and blocking issues in reeled stock.
Performance Boundary
Coating integrity degrades when thermal drying conditions induce solvent boiling and micro-void formation. Excessively fast solvent drive creates surface skins that trap volatile components beneath the coating surface. Matching solvent evaporation rates to line speed and dryer temperature profiles prevents surface skinning and ensures complete solvent removal.
