Agfa-Gevaert Ag

Burkhard Nippe

Heinrich Kober

Walter Meckel

Robert Kohler

Johannes Gerum

Joachim Greiner

Karlchristian Schilffarth

Hermann Perrey

Ernst Grigat

Bernd Quiring

Hermann Brinkmeyer

Bernhard Seidel

Gerhard Hubler

Magnetic recording carriers having improved mechanical properties are obtained by using, as dispersing agents, compounds corresponding to the general formula ##STR1## which are attached to the magnetic pigment by their SO.sub.3 H group and which have reactive groups by which they are linked to the reactive groups of the polymeric binder through a difunctional or higher functional isocyanate.

Process for the production of magnetic recording carriers

This invention relates to a magnetic recording carrier in which the magnetic layer and/or the backing layer contains, in addition to the usual additives, radiation hardenable dispersing agents based on ethylenically unsaturated phosphoric acid ester mixtures capable of forming bataine type stuctures and consisting of reaction products of (A) an acrylic acid ester and/or oligo acrylate containing 1 OH group per molecule, (B) a tertiary alkylamine containing 1 OH group per molecule and (C) phosphorus pentoxide, the reaction products having acid numbers below 200.

Magnetic recording carrier containing radiation hardenable dispersing

What is claimed is a magnetic storage medium in which the polyurethane binder system forms a three-dimensional network independently of reactive low molecular weight substances present on the magnetic pigment or in the dispersion and the production of such a storage medium. The binder in the colored magnetic layer consists of a reaction product of polyisocyanates having an average functionality of from 2.1 to 4 (A) with predominantly difunctional aromatic amino-terminated polyurethanes having an average molecular weight of at least 10,000 (B) and optionally one or more hydroxyl group-containing polyesters having an OH number of from 100 to 450 (C), and/or predominantly difunctional aromatic polyamines having a molecular weight of from 100 to 400 (D) the ratio of isocyanate groups present in (A) to the isocyanate reactive groups present in (B), (C) and (D) being from 0.3:1 to 20:1, preferably from 0.8:1 to 20:1. With this binder system, it has been possible to achieve direct linkage of the polymeric binder chains and to suppress side reactions. This has enabled a soft polyurethane agent to be used, with the result of smooth dispersion of the magnetic lacquer and hence increase in the signal/noise ratio of the magnetic recording medium. The subsequent cross-linking which takes place according to the present invention enables the mechanical properties of the recording medium to be adjusted to the exact result required after the magnetic lacquer has been applied to a support.

Magnetic storage medium

This invention relates to a process for the production of a magnetic recording material having at least one layer of magnetic oxidic and/or metallic needle shaped pigments with dimensional anisotropy and/or some other type of magnetic anisotropy, e.g. crystalline, dielectric or magnetic field induced anisotropy, which process may be used to produce a layer having perpendicular anisotropy or a layer which passes from an initial perpendicular anisotropy to an isotropic distribution of the preferential magnetic axes of the pigments. According to the present process, the magnetic dispersion, after having been applied to the layer support, is subjected to an external magnetic field while still in the state of a liquid suspension, with the result that the pigments move with the preferential axis thereof into the perpendicular axis of the layer, and the pigments are subsequently fixed by drying.

Process for the production of a magnetic recording material with

This invention relates to a magneto-optical storage and playback process for travelling information carriers, by recording on a magnetizable information carrier (1) in the form of a tape, disc or roller while the carrier is in motion, said information carrier having information areas which are larger than 0.2 .mu.m and smaller than 20 .mu.m in one direction of the information plane, the process being carried out by the production of a geometrical structure (4) by the action of the magnetic fields of the recorded information on particles whose greatest length is less than 0.1 .mu.m, preferably 0.02 .mu.m, and by optical scanning of these structures in which light of wavelength 0.38 to 0.8 .mu.m is diffracted on the surface of the moving information carrier (1) and diffraction images are produced which serve for the interpretation of the information.

Magneto-optical storage process

The present invention relates to a magnetic storage medium consisting of a non-magnetic layer support and, applied thereto, a binder-containing magnetic layer, the binder consisting of from 25 to 100% of a thermoplastic polyurethane substantially free from reactive terminal groups obtained by reacting a linear polyester of at least one dicarboxylic acid containing from 2 to 8 carbon atoms and/or hydroxy carboxylic acid containing from 4 to 6 carbon atoms and at least one glycol containing from 2 to 6 carbon atoms, the polyester having a molecular weight of from 1200 to 6000, at least one diisocyanate and a mixture of at least two glycols containing from 2 to 20 carbon atoms, the molar fraction of the individual components not exceeding 0.8. The polyurethane has a hardness of from 80 to 100 Shore A, a tensile strength of from 30 to 75 MPa and a breaking elongation of from 320 to 520%.

This invention relates to the addition of organic boron compounds, prepared by either reacting boric acid with polyhydric alcohols having a total of 5 or more neighbouring OH groups per boron atom and then with polyethylene oxide in a mol ratio of 1:40, based on 1 mol of borate which is obtained, and with a carboxylic acid having from 8 to 22 carbon atoms or reacting boric acid first with polyhydric alcohols having a total of 5 to 11 neighbouring OH groups per boron atoms, and the with a carboxylic acid having from 8 to 22 carbon atoms, said boron compound being added, in a quantity of from 3 to 12, in particular from 3 to 6 parts, by weight, based on 100 parts, by weight, of magnetic pigments, and in particular of metal powders, to the grinding operation of the magnetic pigment dispersion and then processing in a known manner. The necessary degree of dispersion is achieved after a short grinding time compared to known dispersing agents, during which time the pigment particles which are initially lying together are separated into monodisperse individual particles. The favorable effect is expressed by improved alignment values in the finished magnetic tape.

Process for the production of magnetic dispersions containing binders

Magnetic recording medium using water as dispersion medium. The magnetic layer comprises as binder an aqueous dispersion of polyurethane having functional groups capable of salt formation and a magnetic pigment. The volumetric ratio of magnetic pigment to polyurethane in terms of solids content is in the range of 0.7:1 to 1.4:1.

Magnetic recording medium

A magnetic recording material, preferably for tape recorders which are designed for the iron oxide bias setting and for a playback equalization of 120 .mu.s, consisting of a support and at least two layers containing magnetic pigments and binders and differing in coercivity and layer thickness, the uppermost layer containing as acicular, magnetic pigment thermally stabilized magnetite containing from 0.1 to 5% by weight of Cd, Pb, Ca, Mg, Zn, Al, Cr, W, P and/or B based on Fe.sub.3 O.sub.4. The pigments have an average crystallite size of from 30 to 35 nm and a coercivity of from 28 to 36 KA/m. These double-layer tapes have a low bias level and a high dynamic range despite a playback equalization of 120 .mu.s.

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Munich, Germany

Burkhard Nippe