Clay enhances the weatherability, salt spray corrosion and abrasion resistance

The physical, structural and chemical aspects of PU and PU-nano clay coatings have been studied in the present work. Nano clay protects PU chains and functional groups from degradation. The weatherability and corrosion resistance are very important for automotive topcoat. Two types of clay Cloisite 30B (C30B) and Loisite 20A (C20 A), 2K polyurethane (PU) packaging coatings were modified at nanometer scale.

These coatings show better salt spray resistance (500 hours) and accelerated weathering conditions (1000 hours). When observed by atomic force microscopy (AFM), the nano-scale morphology of these nano-composite coatings shows the formation of spherical (C30B) and rod (C20 A) sized hard segments of - 200 nanometers, which is more uniformly formed and evenly distributed across the micro-scale surface (surface texture) than the plain PU coatings.

Better performance of nanocomposite coatings

Spectrum and chemical analysis confirmed that nanocomposite coatings had better performance under ultraviolet / humidity and salt cycle. Dry film thickness and gloss; DFT 1000 (G [1000]) decreased 25% (32%) for pure PU, 14.03% (16.7%) for PU-3C30B and 20% (22.7%) for PU-3C20A. The total color difference of CIELAB value E* of PU, PU-3C30B and PU-3C20A is 9.794, 7.623 and 8.450. For PU, salt spray (500 hours) produces about 35% of low carbon steel (ms panel) area, while for PU-3C30B and PU-3C20A, it only produces 5% and 10% respectively. Fourier transform infrared (FTIR) spectroscopy showed that the functional groups of the aged and corroded nanocomposite coatings were better retained than those of the original coatings. This proves that the interaction between properly peeled two-dimensional clay particles and hard segments plays an important role in resisting weathering, salt spray corrosion and even damage.