Effect of time-dependent reduction of the Cr oxide layer on the interfacial adhesion of polyurethane protective coatings to Cu/Ni/Cr-plated acrylonitrile–butadiene–styrene substrates

초록

In the automotive industry, lightweight design is required to improve fuel efficiency and reduce greenhouse gas emissions. Widely used in automotive interior and exterior components, acrylonitrile–butadiene–styrene (ABS) copolymers exhibit excellent mechanical strength, low density, good processability, and cost-effectiveness, contributing to automotive lightweighting and environmental sustainability. To enhance corrosion and abrasion resistance and decorative properties, ABS substrates are often plated with hexavalent chromium (Cr(VI)). Because this layer alone cannot withstand various external impacts, which result in surface cracking, a polyurethane (PU) coating with superior abrasion and corrosion resistance is typically applied on top of the plating layer. However, insufficient interfacial adhesion between the Cr plating and PU coating layers can cause damages such as delamination and blistering. We found that the interfacial adhesion may vary depending on the surface oxidation state and chemical characteristics of the Cr plating layer, but the underlying chemical adhesion mechanisms have not yet been fully elucidated. Herein, X-ray photoelectron spectroscopy and time-of-flight secondary ion mass spectrometry were employed to investigate the chemical bonding and compositional changes of the Cr oxide layer and Cr plating–PU coating interface. The chemical bonding state of the Cr plating layer underwent a time-dependent chemical evolution during the dwell time under controlled ambient storage conditions. Interfacial analysis between the Cr plating and PU coating layers confirmed that interfacial chemical bonding changes induced by spontaneous reduction were a primary cause of adhesion deterioration. This study provides important insights for designing polymer coating systems and optimizing process conditions to enhance the long-term interfacial stability of Cr-plated components.

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