Bayer Aktiengesellschaft

Helmut Printzen

Bernd Krockert

Gunter Buxbaum

Wilfried Burow

Horst Brunn

Klaus Nollen

Hans-Ulrich Hofs

Karl-Werner Ganter

Hans-Peter Biermann

Low-silking iron oxide yellow pigments having improved color qualities are produced by a novel method which utilizes both precipitation process and the Penniman process. Pigments are nucleated and grown by precipitation to achieve multiplication factor of 2.5 to 7 and additional pigment growth is carried out by the Penniman process.

Process for the production of iron oxide yellow pigments

An improved process is disclosed for preparing iron yellow pigments from iron--(II) salt solutions, in the presence of iron scrap, by injection of air at elevated temperatures. After formation of the pigment, the reaction suspension is stirred without additional gas injection, whereby lighter, purer yellow pigments are obtained.

Process for the preparation of iron yellow pigments

A process for the production of iron oxide yellow pigments by the Penniman-Zoph process from the raw materials iron (II) sulfate, sodium hydroxide and metallic iron, is disclosed in which iron (II) is oxidized to iron (III) by gassing with air in the presence of goethite nuclei, the iron (III) sulfate is dissolved to form iron (II) and the goethite nuclei are built up to iron oxide yellow pigments, characterized in that the gassing with air and dissolving of the metal are carried out in separate vessels.

Iron oxide yellow pigments having a silking effect .DELTA.E.sub.1 *, less than or equal to 0.5, and having color values which range for L* from 52-63, for a* from 8 to 14 and for b* from 40 to 48 CIELAB units are produced by a process by first, forming needle-shaped .alpha.-FeOOH yellow pigment nuclei in the presence of compounds containing the elements B, Al, Ga, Si, Ge, Sn or Pb present in a quantity of from 0.05 to 10% by weight, where the quantity is calculated as the tri- or tetra-valent oxides of the compounds and based on the .alpha.-FeOOH which is precipitated during nucleation, and second, growing iron oxide yellow pigments on the thus formed iron oxide yellow nuclei.

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Krefeld, Germany

Helmut Printzen