UV Absorber UV-360 (Benzotriazole, High MW, Low Migration)

UV absorber effectiveness depends not just on absorption spectrum but on retention within the coating film over years of UV exposure and rain washing. Low-MW UV absorbers (MW <300) migrate and surface-bloom readily, losing effectiveness within 1–3 years. High-MW benzotriazoles (MW 600–800) have much lower diffusion coefficients, reducing migration by 10–100×. For automotive OEM clearcoats (10+ year durability targets), high-MW or polymeric UV absorbers are required. High-MW types also show better compatibility with HALS light stabilizers (no antagonism), enabling synergistic UV protection systems.