Basf Aktiengesellschaft

Fritz Hammon

Manfred Ohlinger

Job-Werner Hartmann

Heinz Stritzinger

Walter Schneider

Georg Schnell

Eduard Schoenafinger

Eduard Kaemmer

Karl-Juergen Reimer

Horst Grosselfinger

Philipp Pister

Franz Buettner

Hans-Peter Reuther

Uwe Heim

Dispersions consisting essentially of finely divided materials homogeneously distributed in solutions of organic polymers are applied structure-free to flexible base materials in tape form by means of a knife coater.

Structure-free application of dispersions to flexible base materials

The surface character of flexible materials is examined by means of interference fields which are formed by reflection of light beams from a reflecting reference surface and from the adjoining surface to be examined, and subsequent super-position of the partial beams thereby formed. The interference field which corresponds to the surface profile standing out from the reference surface is utilized to determine the length and height of the surface profile, with the aid of the interference band spacings and the wavelength of the incident light.

Process and apparatus for the surface analysis of flexible materials

In order to determine the homogeneity of a magnetic dispersion, part of the dispersion is conducted through a measuring cell prior to its application to a base, the size, number and type of those regions of the magnetic dispersion which interfere with the homogeneity being determined with the aid of magnetic measurements. The measuring cell contains a magnetic head, a magnetic dispersion is made to flow in a stream of constant cross section past the air gap of the magnetic head, and a magnetic field at least partially penetrating the magnetic dispersion is produced. From the characteristics of the amplified output voltage of the magnetic head the various parameters of the inhomogeneities in the magnetic dispersion can then be ascertained.

Method and device for determining the homogeneity of magnetic dispersions

The invention relates to a process for improving the magnetic properties, especially the remanent magnetization, of gamma-iron(III) oxide which can be used advantageously as the magnetic component in magnetic recording media exhibiting reduced print-through. For this purpose, a gamma-iron(III) oxide manufactured according to known processes is heated at temperatures of from 400.degree. to 700.degree. C., the magnetic pigment having basic compounds on the crystal surface during this heat treatment and retaining a pH value above 8 until heating is over. Gamma-iron(III) oxide magnetic pigments treated in this way are particularly suitable for the manufacture of low-noise magnetic recording media with high remanent magnetization and particularly low print-through.

Improving the magnetic properties of gamma-iron (III) oxide

A flexible multilayer magnetic recording medium exhibiting an improved signal-to-print-through ratio coupled with an improved maximum output level and diminished dc noise, comprising a non-magnetic base and, applied thereto, at least two superposed layers consisting of a binder with magnetizable particles uniformly dispersed therein, the upper magnetic layer containing a magnetic pigment giving a signal-to-print-through ratio of less than 55db and the lower magnetic layer(s) containing a magnetic pigment giving a signal-to-print-through ratio of 55 db or more.

Flexible multilayer magnetic recording medium

Flexible multi-layer magnetic recording media comprising a non-magnetic flexible base and, applied thereto, two superposed magnetizable layers which contain a homogeneous mixture of acicular magnetic chromium dioxide in an organic binder. According to the invention, the magnetizable layer adjacent to the base contains a chromium dioxide having a specific surface area, measured by the BET method, of from 15 to 25 m.sup.2 /g, while the outer magnetic layer contains a chromium dioxide having a specific surface area, measured by the BET method, of from 26 to 35 m.sup.2 /g. Such magnetic recording media are distinguished by uniformly high sensitivity over the entire audible frequency range even if close manufacturing tolerances are not maintained.

Flexible multi-layer magnetic recording media

This invention concerns methods and devices for switching a tape-recorder or cassette tape-recorder and especially recorders on which tapes with different magnetic coatings can be used. According to the invention, at least one section along the magnetic tape which has a much higher electric resistance than the magnetic coating is used in conjunction with arrangements of simple layout and in advantageous manner to monitor the resistance of the tape either continuously or sporadically, and at least one predetermined switching state of the recorder is allocated to each different resistance value. This ensures reliable switching of any such states as 'machine on', 'machine off' or 'iron oxide (chromium dioxide) tape' bias, without any other special changes at the magnetic tape or at the cassette.

Growing community of inventors

Frankenthal, Germany

Fritz Hammon