Non-silking iron oxide yellow pigments with high color density

US6053972A · kind A · utility

Assignee

• BAYER HEALTHCARE LLC · DE

Inventors

• Ulrike Pitzer · Krefeld, DE
• Rolf Naumann · Krefeld, DE
• Rolf Braun · Offenbach, DE

Key dates

• Filing date: Nov 16, 1998
• Grant date: Apr 25, 2000
• Expiry date: Nov 16, 2018

Classification

• Technology area (CPC C): Chemistry; Metallurgy
• CPC primary: C01P2006/60
• WIPO field: Basic materials chemistry
• WIPO sector: Chemistry

Abstract

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 PA1 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 Al.sub.2 O.sub.3, with respect to precipitated .alpha.-FeOOH, and subsequent oxidation to .alpha.-FeOOH and PA1 b) pigment growth is performed by precipitating further iron with simultaneous oxidation, wherein the seed/time yield is less than 0.3 h.sup.-1 and the pH value is less than 3.9 over the entire period of pigment growth and PA1 c) pigment growth is terminated at a reproduction factor between 3 and 20.