Basf Magnetics Gmbh

Basf Magnetic Gmbh

Attila Vass

Hans-Heinrich Credner

Wolf-Dieter Schroeer

August Lehner

Werner Lenz

Norbert Schneider

Werner Loch

Gregor Brodt

Wolf-Dieter Schroer

Guenther Kuntz

Juergen Sauter

Juergen Schmidt

Hildegard Fischer

In the preparation of dispersions of magnetic pigments, it was found that excellent dispersion stability is achieved when compounds which are selected from the group consisting of quaternary ammonium compounds, guanidines, piperidines, alkylated or ethoxylated amines, diamines, polyamines or mixtures thereof, ethanolic KOH solutions, metal alkoxylates, Grignard compounds and certain metal hydrides are used as codispersants. The compounds are added in an amount of 0.15-4% by weight, based on the magnetic pigment.

Magnetic coating dispersion

In magnetic recording media consisting of a nonmagnetic substrate and at least one magnetizable layer firmly applied thereon and based on magnetic material dispersed in a binder mixture which contains at least one hydroxyl-containing, preferably low molecular weight polyureaurethane and one polyurethaneurea (meth)acrylate, the polyurethaneurea (meth)acrylate is obtained by reacting a poly(meth)acrylate having up to 2 terminal OH groups per mol and a molecular weight of from 200 to 50,000 with a mixture of aliphatic polyisocyanates having an average functionality of from 3.0 to 6.0 NCO groups per mol, consisting of from 0.1 to 10% by weight of a diisocyanate, from 30 to 80% by weight of a triisocyanate and from 20 to 60% by weight of an isocyanate having a functionality of from 4 to 10, with the proviso that from 1.2 to 3.0 NCO groups react per OH group and the remaining NCO groups are converted into substituted terminal urea groups with a polyfunctional amine or with a mixture of different polyfunctional amines.

Magnetic recording medium containing magnetic material dispersed in a

A magnetic dispersion comprising finely divided iron power or iron alloy powder having a BET value of more than 35 m.sup.2 /g dispersed in a polymeric binder and organic solvent, whose filterability is markedly improved, is obtained by using certain low molecular weight phosphoric esters of the general formula I or II ##STR1## combined with a dispersion-active compound which contains at least one polar group capable of adsorption on the magnetic pigment. The polar group of the dispersion-active compound can be an acid or alkaline or amphoteric group or a group capable of hydrogen bonding or polarization. The dispersion-active compound can be a polycondensate, a polyaddition product or a chain growth copolymer which can also be used in the magnetic dispersion combined with customary other polymeric binders.

Magnetic recording medium comprising a polyoxyalkylene oxide binder, a

In the preparation of dispersions of magnetic pigments in organic solvents, dispersants which have a sterically stabilizing effect are used. Milling results in division of the pigment aggregates, which combine again as a result of attractive forces to give secondary agglomerates in the event of poor stabilization. These flocculating materials must be removed from the dispersion by expensive filtration. If an increase in the fineness or pigment batch fluctuations lead to an increase in the secondary agglomerates, filter breakthroughs may occur, resulting in a dramatic reduction in the yield of magnetic recording medium. It was found that excellent dispersion stability is achieved when the magnetic pigments are first precoated with a long-chain dispersant. Subsequently, the use of charge-generating, low molecular weight codispersants, a charge build-up on the pigment is specifically induced by means of bases or acids. The electrostatic repulsion which additionally becomes effective leads to an increase in the dispersion stability. The charges on the pigment are monitored by means of ESA measurements (electrokinetic sound amplitude). These ESA measurements make it possible to establish the order of addition of the dispersants and the optimum amount of codispersant.

Magnetic recording medium having a magnetic layer prepared from magnetic

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Munich, Germany

Attila Vass