Transparent UV-cured Phosphorus/Nitrogen Hybrid Coating for Simultaneously Enhancing Flame Retardancy and Surface Hardness of Polycarbonate

The flame-retardant monomer PG (P) was synthesized from diethylphosphinic acid and glycidyl methacrylate (GMA). Simultaneously, the phosphorus-containing flame-retardant monomer, TAEP (T), was synthesized from phosphorus oxychloride and 2-hydroxyethyl acrylate. A 50 µm thick transparent UV-cured coating, designated MAAR-P 8 T 4 , was successfully constructed on 0.5 mm thick polycarbonate (PC) films by blending PG and TAEP with melamine acrylate resin (MAAR). The fabricated coating demonstrated a high transmittance of 91.9% in the visible-light spectrum. The incorporation of monofunctional PG effectively regulated the system viscosity and mitigated curing shrinkage stress. Furthermore, the synergistic action of phosphorus in different valence states and nitrogen from MAAR imparted a dual gas-phase-condensed phase flame-retardant mechanism to the coating, enabling the PC substrate to attain a V-0 rating in the UL-94 vertical burning test. This research indicates that the MAAR-P 8 T 4 coating engineered via molecular design and component optimization concurrently overcomes the limitations of PC, namely its low surface hardness and inherent flammability. A straightforward and efficient preparation strategy provides a practical approach for transparent flame-retardant coatings for electronic and electrical applications.