Laminating Adhesives Chemicals

Solventless two-component polyurethane (2K PU) adhesives dominate flexible packaging for their low VOC, fast line speed (up to 600 m/min), and excellent bond strength on OPP, PET, BOPA, and PE films. Solvent-based PU adhesives are used for demanding applications (retort pouches, high-barrier films). Waterborne adhesives serve lower-performance commodity laminates. Electron-beam (EB) curable adhesives are emerging for ultra-low migration applications.

Adhesion to low-surface-energy films (PE, PP) requires corona treatment (≥42 dyne/cm) immediately before lamination. Primer coatings (polyethyleneimine, polyurethane) improve adhesion on difficult substrates and barrier coatings (EVOH, SiOx, AlOx). Silane coupling agents in the adhesive formulation promote bonding to aluminum foil and metallized films. Bond strength is measured by T-peel (ASTM F904) and 90° peel tests.

EU Regulation 10/2011 (plastic food contact materials) requires overall migration ≤10 mg/dm² and specific migration limits for individual substances. US FDA 21 CFR 175.105 regulates adhesives for food contact. Solventless PU adhesives must demonstrate low aromatic diamine (PAA) migration — controlled by using non-aromatic isocyanates (HDI, IPDI) and ensuring full cure. Suppliers provide compositional declarations and SML data for regulatory compliance.

Pot life of solventless 2K PU adhesives is typically 4–8 hours at 40°C working temperature, determined by isocyanate index and reactive component selection. Viscosity build during pot life is monitored — adhesive viscosity should remain below 1000 mPas at application temperature for consistent coat weight. Longer pot life requires lower reactivity isocyanate or MDI/HMDI blends. Temperature control of the adhesive pan is essential for process consistency.

Retort pouches (121°C steam sterilization) require bond strength ≥3.5 N/15mm after retorting for all laminate interfaces (PET/Al, Al/CPP). Adhesives must maintain performance after extended hot-fill or sterilization cycles with no delamination, tunneling, or bond failure. High-functionality polyol components and aliphatic isocyanates (HDI) give the best thermal stability. Bond strength is tested after retort per ASTM F88.