Encapsulation of aluminum flakes with KH550, silica sol, and stearic acid for the preparation of waterborne Al@KH550@SiO2@SA composite pigments

Abstract

Waterborne aluminum flake composite pigments (Al@KH550@SiO₂@SA) were prepared by successively encapsulating aluminum flakes with hydrolyzed γ-aminopropyl triethoxysilane (KH550) inside nanolayer, SiO₂ intermediate inorganic nanolayer, and stearic acid (SA) outside organic layer. Hydrolyzed KH550 nanoparticles anchored at the surfaces of Al flakes via Si–O–Al bonding, SiO₂ nanoparticles anchored at the hydrolyzed KH550 nanolayers via Si–O–Si bonding, and stearic acid molecules anchored at the SiO₂ intermediate nanolayers via the interaction between carboxylic groups and surface –OH groups. The encapsulation of SiO₂ intermediate nanolayer using environmentally friendly silica sol precursor obviously improved the anticorrosion performance of resultant composite pigments. The encapsulation of stearic acid outside organic layer endowed the composite pigments with good water floating performance. The lightness, brightness, and whiteness of encapsulated aluminum flake composite pigments are comparable to those of solventborne aluminum flake pigment.