Bayer Aktiengesellschaft

Bayer Aktiengeselschaft

Peter Kiemle

Aloys Eiling

Gunter Buxbaum

Franz Hund

Fritz Rodi

Jurgen Wiese

Hendrik Kathrein

Wilfried Burow

Horst Brunn

Wolfgang Rambold

Ingo Pflugmacher

Heribert Bade

Gerd-Hermann Schulten

Acicular magnetic iron oxide pigments are disclosed which have a Co content of 1 to 5% by weight and an FeO content of 5 to 12% by weight. The pigments may optionally contain an additional dopant selected from zinc, phosphate and SiO.sub.2. The pigments are useful in magnetic recording media such as video tapes.

Co-containing magnetic pigments, processes for the production thereof

Magnetic iron oxide pigments useful in magnetic signal recordings having a dependence of coercivity on temperature in the temperature range of from 76K to 298K of less than 0.13 kA/mK and having a coercivity on powder compressed to 0.9 g/cm.sup.3 of greater than 51 kA/m are prepared by coating a magnetic iron oxide core material having the composition FeO.sub.x where x is a number from 1.33 to 1.5 in a first step with a compound containing divalent and trivalent iron having a ratio of Fe(III): Fe(II) from 0.01 to less than 2, and then in a second step coating the pre-coated core with a second coating of a cobalt compound.

Magnetic iron oxide pigments and a process for their preparation

Magnetic iron oxide pigments having a monomolecular coating of a cobalt compound useful in magnetic signal recordings having a dependence of coercivity on temperature in the temperature range of from 76 K to 298 K of less than 0.13 kA/mK and having a coercivity on powder compressed to 0.9 g/cm.sup.3 of greater than 51 kA/m are prepared applying a preliminary coating of Fe.sub.3 O.sub.4 or a bertholloid compound to a magnetic iron oxide core material having the composition FeO.sub.x where x is a number from 1.33 to 1.55 and then covering the preliminary coating with a cobalt compound.

Isometric oxidation resistant and heat resistant iron oxide black pigments having a foreign metal content of less than 5 ppm of each of As, Pb and Ba, less than 200 ppm total of Ca, BaSO.sub.4, Zn, Sb and Cr and from 0.05 to 2% by weight, calculated as trivalent or tetra-valent oxides, of B, Al, Ga, Si, Ge and Sn, are useful in coloring lacquers, thermoplastic synthetic resins and building materials as well as for low coercivity iron oxide black pigments in magnetic toners.

Oxidation resistant, heat resistant iron oxide black pigments, a process

In improved cobalt coated magnetic iron oxide having increased coercive field strength and highly efficient for use in magnetic recording devices and processes is produced by subjecting uncoated magnetic iron oxide particles to an acid treatment and then epitaxially coating the treated particles with cobalt.

Process for the production of iron oxides epitaxially coated with cobalt

A process for increasing the color purity of iron oxide pigment particles admixed with color-modifying impurities and obtained by the Penniman process or the aniline process, comprising introducing the particles into a magnetic field, and removing from the magnetic field two fractions of different magnetizability, the first fraction being iron oxide pigment particles of increased color purity and the second fraction being enriched in impurities.

Magnetic separation to improve purity of iron oxide pigments

In the production of needle-shaped magnetic iron oxide pigments by treating iron with a nitro-aromatic in the presence of .alpha.-FeOOH nuclei to form .alpha.-FeOOH particles and an amino-aromatic, and thereafter dehydrating the .alpha.-FeOOH particles and reducing them, the improvement which comprises forming the .alpha.-FeOOH nuclei at about 0.degree. to 90.degree. C. in a suspension of metallic iron, an iron-(II)-salt and a nitro-aromatic by adding a basic precipitant in about 10 to 95% of the amount required for the complete precipitation of the iron in the iron-(II)-salt. Advantageously the metallic iron comprises cast iron, the nitro-aromatic comprises nitrobenzene, the amino-aromatic comprises aniline, the basic precipitant comprises at least one of ammonia and a basically reacting alkali metal, alkaline earth metal or ammonium salt, the nuclei formation is carried out at about 10.degree. to 60.degree. C., and the basic precipitant is added in about 20 to 80% of the amount required for the complete precipitation of the iron in the iron-(II)-salt, additional iron and nitrobenzene being added to the suspension of precipitated nuclei to form the .alpha.-FeOOH particles.

Growing community of inventors

Krefeld-Traar, Germany

Peter Kiemle