Preparation of interference pigments using black graphite nanosheets†
Consumer desire for attractive colors necessitates the development of novel pigments that are eco-friendly and durable. The pigments prepared in the present work exhibited enhanced colors caused by thin-film interference through absorption of scattered light by black materials. The graphite nanosheet (GNS) pigments contain no heavy metals and are nonfading pigments composed of exfoliated graphite and TiO2. GNSs, as a novel substrate for interference pigments, were prepared by wet dispersion with a dispersant and a hydrogen peroxide–urea complex to maintain a sheet structure with few defects. We demonstrate for the first time that GNSs that exhibit good dispersibility in water can be prepared via a simple procedure. The GNS pigments were obtained by sol–gel deposition of a TiO2 layer onto dispersant-modified GNSs. Various colors were developed by adjusting the thickness of the TiO2 film by varying the reaction time. Because of the light-absorbing properties originating from the black GNSs and diffuse reflection derived from the random orientation of the GNS pigment in the coating, the coating film exhibited enhanced colors with angle independence.