Non-silking iron oxide yellow pigments with high color density

摘要

Non-silking iron oxide yellow pigments with high color density. Iron oxide yellow pigments in the alpha -FeOOH modification with a silking index of less than 5 were obtained in which a) alpha -FeOOH seeds are produced by precipitation from an Fe(II)-containing solution with an alkaline precipitating agent in the presence of soluble aluminium salts in an amount of 3 to 9 wt. %. calculated as Al2O3, with respect to precipitated alpha -FeOOH, and subsequent oxidation to alpha -FeOOH and b) pigment growth is performed by precipitating further iron with simultaneous oxidation, wherein the seed/time yield is less than 0.3 h-1 and the pH value is less than 3.9 over the entire period of pigment growth and c) pigment growth is terminated at a reproduction factor between 3 and 20.