Hard transparent coatings on thermoplastic polycarbonate

Thermoplastic polycarbonates are widely used in several manufacturing domains because of their extraordinary combination of transparency, toughness, ductility and chemical inertness at low and moderate temperature. They are, thus, ideal candidates to substitute float glasses, where lightweight and safety are of utmost relevance. In contrast, polycarbonates feature limited scratch and mar resistance, being characterized by very low surface hardness. This suggests the protection of polycarbonates with hard transparent coatings. However, poor interfacial adhesion between conventional coatings and polycarbonates, reduced cohesive strength of some hard coating materials and, in particular, their limited compliance when deposited on ductile substrates often reduce significantly their performance. In this respect, the present work analyzes the pros and cons of protecting thermoplastic polycarbonates with specialty coatings, emphasizing the real advantages of applying surface overlying layers and their drawbacks. Different formulations of the coatings were herein studied to optimize their interfacial adhesion with polycarbonates and cohesive strengths. Tribological (scratch, wear and mar) tests were, thus, performed to assess the performance of the coatings. After appropriate designing, specialty coatings might be useful to increase hardness and mar resistance of polycarbonates. Nevertheless, they are still largely ineffective to improve wear resistance of polycarbonates.