Bayer Aktiengesellschaft

Lutz Leitner

Gunter Buxbaum

Franz Hund

Rolf Naumann

Friedrich Jonas

Ottfried Schlak

Jakob Rademachers

Artur Botta

Helmut Steinberger

Heinrich Heine

Ingo Pflugmacher

Heinrich-Christian Schopper

Hans-Peter Biermann

Volker Hahnkamm

Peter R Schick

An improved magnetic dispersion for magnetic recording which comprises magnetic pigment, abrasive, carbon black or another additive for regulating conductivity, binder, solvent, lubricant, and wetting agent, wherein the improvement comprises quantities of wetting agent, lubricant, or both being between at least 100 to 140% of the individually determined saturation adsorptions of the wetting agent and lubricant, with the proviso that the minimum quantity of wetting agent or lubricant is 80% of the individually determined saturation adsorption.

Magnetic lacquer dispersions, process for their production and their use

A magnetic pigment consisting essentially of iron, having an X-ray crystallite size with the 110 reflex of from 14 to 22 nm, a coercive force from 55 to 88 kA/m and a switching field distribution of the oriented pigment particles of less than 0.55 is produced by precipitating an iron (II)-salt with a super-stoichiometric quantity of an aqueous alkali metal carbonate solution and oxidizing it to produce .alpha.-FeOOH, .gamma.-Fe.sub.2 O.sub.3, Fe.sub.3 O.sub.4 or betholoid iron oxides, subsequently reducing it to the metal, and providing the iron oxides or oxide hydroxides with an inorganic protection from sintering at the latest during reduction.

Preparation and use of iron magnetic pigments

Readily dispersible finely divided solids such as pigments, coated with an organo-silicone polymer of the formula ##EQU1## wherein R.sup.I, R.sup.II, R.sup.III each independently is an optionally halogenated alkyl, alkenyl or aryl radical having from 1 to 10 carbon atoms;

Readily dispersible silicone-coated finely divided solids

A pigment of a magnetic metal or alloy thereof carrying, in about 0.2 to 30% of the weight of the metal or alloy, a coating of at least one member selected from the group consisting of an ortho-silicic acid ester, a hydrolyzate thereof and a condensation product thereof. Optionally it also carries a corrosion inhibitor. The coated pigment is produced by suspension of the untreated pigment in a liquid medium containing the ortho-silicic acid ester or derivative thereof, and optionally the corrosion inhibitor, followed by separation and drying at 50.degree. to 250.degree. C. The resulting pigment is non-pyrophoric and of high performance properties suitable for use in magnetic recording media.

Magnetic metal and alloy pigments

A cobalt-doped, acicular ferrimagnetic iron oxide having an FeO content of about 16 to 24%, by weight, and a cobalt content of about 0.7 to 2.4%, by weight, the coercive force amounting to at least about 425 Oe+175 Oe/%, by weight, of Co is produced by precipitating and oxidizing a cobalt-containing aqueous iron (ii) salt solution, reducing the precipitate to Fe.sub.3 O.sub.4, partially reoxidizing to adjust the FeO content and heat treating under inert conditions at a temperature from about 600.degree. to 800.degree. C.

Production of cobalt-doped ferrimagnetic iron oxides

An acicular to prismatic ferrimagnetic iron oxide pigment with a porosity of less than about 10% by volume, and optionally containing up to about 15% by weight of other metal oxides such as Zn or especially Co, are produced by heating a suspension of iron(III)oxide hydroxide in an autoclave to a temperature above about 100.degree. C in the presence of at least one mono-, di- or tri-saccharide, at least one alkali metal or alkaline earth metal hydroxide or carbonate and excess water, and washing, filtering and drying the resulting pigments.

Hydrothermal process for producing dense iron oxide pigments

In the production of acicular, ferromagnetic iron oxide of high coercive force by oxidizing an iron (II)-hydroxide suspension with an oxygen-containing gas to form acicular iron (III) oxide hydroxide and dehydrating the iron (III) oxide hydroxide, optionally tempering, reducing and/or reoxidizing this into magnetic iron oxide, the improvement which comprises effecting the oxidation of the iron (II)-hydroxide suspension at a pH of at least about 13, the suspension including SiO.sub.2 in the form of a sol or soluble salt, the resulting iron (III) oxide hydroxide having SiO.sub.2 deposited thereon.

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Krefeld, Germany

Lutz Leitner