Basf Aktiengesellschaft

Basf Magnetics Gmbh

Emtec Magnetics Gmbh

Dynamit Nobel Aktiengesellschaft

Imation Corporation

Basf Aktiengesellschat

Helmut Jakusch

Werner Steck

Peter Rudolf

Manfred Ohlinger

Ronald J Veitch

Eberhard Koester

Jenoe Kovacs

Rainer Feser

Guenter Vaeth

Werner Loeser

Wilhelm Sarnecki

Milena Melzer

Albert Kohl

Peter Heilmann

Ekkehard Schwab

Hartmut Hibst

Werner Balz

Norbert Schneider

Harald Jachow

Rudi Lehnert

Werner Lenz

Claus-Dietrich Seiler

Laszlo Marosi

Werner Loch

Heinz Nestler

Werner Grau

Paul Deigner

Jurgen Amort

Ria Kress

Norbert Mueller

Volker Koch

Herbert Haberkorn

Werner Huebner

Otto Ambros

Volker Arndt

Rudolf Brodt

Johannes Sandrock

Eduard Schonafinger

Erich Hoffmann

August Lehner

Helmut Auweter

Gregor Ley

Gerd Wunsch

Joachim Hack

Herbert Motz

Dieter Schaefer

Michael Bobrich

Eduard Schoenafinger

Hans Henning Schneehage

Hans-Joerg Hartmann

Christof Jaeckh

Horst Autzen

Reinhard Polke

Klaus-Dieter Hoppe

Andreas Ilmer

Werner Senkpiel

Udo Kullmann

Hans-Bertram Wiegemann

Reinhard Koerner

Gustav Loewenberg

Heinrich Mannsperger

Gerhard Soehring

Stefan M&uuml;ller

Johann Voit

Eberhard Koster

Werner Loser

Gunter Schadel

Gunter Vath

Bernd Meyer

Hansj&ouml;rg Traub

Peter Stehle

Werner Sickmueller

Reinhard K Orner

Stefan Müller

Werner H&uuml;bner

Bernd H Oppner

Klaus Gotz

Hans-Georg Gottmann

Hartmut Heene

Hans-Joachim Jenor

Multilayer magnetic recording medium which is suitable for high recording densities and the recording of digital data, has very good electromagnetic recording properties and good surface smoothness and can absorb a large amount of lubricant in the lower layer and has at least one upper magnetic recording layer less than 0.5 &#x3bc;m thick and at least one lower layer which contains a magnetically soft pigment.

Magnetic recording medium

Multilayer magnetic recording medium is suitable for high recording densities and the recording of digital data, has very good electromagnetic recording properties in the entire recording wavelength range and good mechanical properties and possesses a flat frequency response and which has at least one upper magnetic recording layer less than 0.5 &mgr;m thick and at least one lower layer which contains a magnetically soft pigment.

A magnetic recording medium which consists of at least two layers cast one on top of the other is described, the lower layer containing acicular magnetic pigments having a field strength of 5-40 kA/m and a magnetization of 20-70 nTm,/g and the upper layer containing a high-density metal powder dispersion. After application of the layers, the magnetic recording medium is subjected to a magnetic disorientation treatment while the layers are in the wet state, so that said recording medium has virtually no magnetic and mechanical anisotropy. The magnetic recording medium produced in this manner is particularly suitable for floppy disks having a high storage capacity of substantially more than 100 megabytes.

Magnetic recording medium having a high recording density and its production

Described are tape-type magnetic recording media (I) including a non-magnetic substrate (III), at least one film applied to the substrate and, in at least one of these films, an inorganic acicular pigment (II) suitable for use as a supporting pigment, the ratio of the mean length to the mean diameter of the pigment (II) being at least 3 and the mean modulus of elasticity of the films being not less than 15 GPa in the longitudinal direction of the tape-type recording medium (I).

Magnetic recording media

A magnetic recording medium consisting of a nonmagnetic substrate and at least two magnetizable layers which are applied thereon and contain metal oxides as magnetic pigment is described, the pigment of the upper layer having a higher BET value than that in the lower layer. According to the invention, the upper layer has a thickness in the range of 3-5 .mu.m when dry and the lower layer a thickness in the range of 1.1-3 .mu.m when dry. Particularly advantageous results are obtained when the magnetic pigment of the upper layer is cobalt-doped .gamma.--Fe.sub.2 O.sub.3 and that of the lower layer is acicular CrO.sub.2. With the double-layer recording medium obtained according to the invention, in particular the output level at low frequencies is improved without the frequency curve showing the usual depression in the middle.

A finely divided acicular CrO.sub.2 modified with iron, tellurium and/or antimony and having a high coercive force possesses improved heat stability of the residual induction and a relatively narrow distribution of the particle size and of the coercive force. This CrO.sub.2 pigment is obtained by a method in which the iron compound used for the modification is iron oxalate, which is employed in an amount of 1-10% by weight, based on the theoretical CrO.sub.2 yield.

Finely divided acicular magnetic modified chromium dioxide

An apparatus for checking deep-frozen food, which irreversibly indicates if an additional storage temperature has been exceeded, is described. A flat plastic bag having transparent walls, into which eutectic mixture having a liquid/solid phase transition in the range from 0.degree. to -50.degree. C. has been introduced, together with a magnetic dispersion consisting of finely divided magnetic pigments, has a heat-conducting connection to the material to be frozen. A magnetic stripe which contains a magnetically recorded pattern and which remains connected to the bag until the indicating apparatus together with the material to be frozen has been cooled below the limiting temperature is stuck to the bag. The magnetic stripe is then removed. If the permissible limiting temperature is exceeded, the optically or magnetically readable structure produced by the magnetic stripe in the indicator bag is eliminated, permitting easy checking of the deep-frozen food. The present invention permits many potential variations by combination of a plurality of applied magnetic stripes.

Temperature indicator for deep-frozen products

A magnetic recording medium comprising a nonmagnetic substrate and at least one magnetic layer applied thereon and containing an acicular chromium dioxide uniformly distributed in a polymeric binder and additives and having a coercive force of at least 60 kA/m, a mean particle length of the chromium dioxide of less than 300 nm, whose factor HD according to the formula ##EQU1## where KT is the coercive force of the magnetic layer in [kA/m], measured in an external field of 380 kA/m, L is the mean particle length and .DELTA.L is the range of the particle size distribution, determined from the numerical distribution of the particle length, both measured in [nm], is greater than 1.85, and a process for the preparation of this chromium dioxide.

Process for preparing modified chromium dioxide

A process for the production of magnetic recording media having stochastic orientation of the magnetic anisotropic particles in the magnetic layer with the aid of a magnetic drum rotating above the still fluid dispersion layer and containing radially arranged permanent magnets of alternating polarity, and a corresponding apparatus for carrying out the process.

Stochastic orientation of magnetic recording media

A method and an arrangement for reducing wear in magnetic storage means having magnetic disks, in particular having flexible media, become effective when predetermined maximum waiting times of the heads on the same track or the same tracks have elapsed. The heads HD are moved away from the waiting tracks in accordance with the predetermined control scheme, may be moved in waiting areas of the magnetic surface, and are moved back to the waiting position.

Method and arrangement for reducing wear in a magnetic storage means

Acicular ferromagnetic chromium dioxide is stabilized by treatment with an alkali metal hydroxide in an aqueous alkaline suspension at elevated temperatures.

Stabilization of acicular ferromagnetic chromium dioxide

In magnetic recording media which have at least one magnetizable layer firmly applied to a nonmagnetic base, the magnetizable layer essentially consists of a magnetic material finely dispersed in an organic polymer binder, a dispersant, a lubricant and other conventional additives.

Ferromagnetic metal particles of substantially iron are prepared by starting from an acicular .alpha.-FeOOH, applying a shape-stabilizing finish to the particle surface, heating at 500.degree.-850.degree. C. and subsequently reducing with gaseous reducing agents at 200.degree.-500.degree. C. to the metal, and starting .alpha.-FeOOH being prepared in the presence of zinc and phosphate ions.

Preparation of acicular ferromagnetic metal particles of substantially

Finely divided, acicular and pore-free .alpha.-Fe.sub.2 O.sub.3 is prepared from iron(III) salts in the presence of one or more organic substances which form complexes with iron(III) ions, in alkaline suspension, at from 80.degree. to 250.degree. C.

Preparation of acicular .alpha.-Fe.sub.2 O.sub.3

Ferromagnetic chromium dioxide is improved by subjecting chromium dioxide materials prepared by a known method to an additional heat treatment.

Preparation of ferromagnetic chromium dioxide

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Frankenthal, Germany

Helmut Jakusch