Fast, Localized, and Low-Energy Consumption Self-Healing of Automotive Clearcoats Using a Photothermal Effect Triggered by NIR Radiation

Dynamic polymer networks containing photothermal materials have been reported to demonstrate highly efficient intrinsic self-healing under irradiation. In particular, organic near-infrared-absorbing ionic salts, such as diimmonium dyes, function as transparent polymer heaters and can enhance the self-healing properties of clearcoats. In this study, we designed a self-healing automotive clearcoat with a reversible polymer network based on acryl polyol (AP) and dynamic hindered urea (HU) bonds and introduced N-butyl-substituted diimmonium borate dye (DID) as a photothermal dye. To optimize the self-healing efficiency of the clearcoat and its transparency in the visible light region, the effects of the presence or absence of dynamic HU bonds and the concentration of the photothermal dye were precisely investigated. For a polymer system containing HU with 0.1 wt % DID (AP/HU-DID_0.1), the transparent automotive clearcoat was heated to ∼70 °C under focused sunlight irradiation and exhibited excellent (∼100% healing efficiency) and fast (<30 s) scratch-healing performance compared with a commercial automotive clearcoat. In addition, this photothermal effect-based self-healing clearcoat exhibited outstanding transparency (over 95%) and has a strong advantage with respect to energy consumption because it enables faster and more localized healing compared with thermal healing processes that require heating the entire product.