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The uppermost pigment particles of a magnetic coating are covered by a thin layer of organic material. Compared to the bulk of the binder formulation, this layer is highly inhomogeneous. At the phase boundaries to air and pigments, concentration gradients are observed which influence the mechanical behavior of the coating, especially when changes take place that are effected by time and climatic conditions. By applying ESCA and SIMS techniques, important information on this surface layer could be obtained concerning: (1) the thickness of this layer, its distribution, and its differences between magnetic and nonmagnetic particles; (2) the incompatibilities and varying distribution of the components of a given formulation; and (3) the mobility of low molecular additives (alteration during changes of climatic conditions or transfer of substances onto contacting bodies). >

Experience with helical-scan videotape recorders has shown that the mechanical forces involved in handling the tape are sometimes sufficient to cause significant reductions in signal level due to stress demagnetization. A tape-loop recorder was used in an investigation of stress demagnetization in videotapes. Results are presented illustrating the magnitude of stress demagnetization and its dependence on the type of tape and the number of applications of stress. The bending stress resulting from the wrap of the tape around guides was studied in considerable detail. It is found that bending stress can greatly exceed other stresses involved in the normal handling of tape. Results are presented to show how bending-stress demagnetization depends on the depth of recording in the magnetic coating and on the radius of the guide. It is found that there is also a strong dependence on wrap angle around the guide. A new analysis is presented to explain the wrap-angle dependence and to permit calculation of bending-stress demagnetization.

Calendering of magnetic tape is applied to achieve a smooth magnetic coating. The purpose of this study is to gain a better understanding of the calendering process. The investigation is focussed on the roughness and elastoplastic deformation of the uncalendered coating, the substrate and the compliant roll material. It is found that these properties do determine the calendering efficiency to a great extent. Model calculations that are performed using the actual elasto-plastic deformation properties of coating and substrate, confirm the experimental results. A small-scale calender is developed with which coatings are calendered by means of a rolling ball. In this way small samples can be used and a large flexibility is obtained. Surface roughness and modulation noise are measured in order to characterize the calendering efficiency. The elasto plastic deformation properties are determined by means of ultra-microindentation measurements. Implementation of the results of this study resulted in an average surface roughness of 4 nm on lab-scale and of 6 nm on semi-production scale.

In this paper the advantages of connecting a tensile tester to a microcomputer are described. The advantage of this combination compared with the combination of tensile tester and conventional available data analyzer is a much better accuracy of the measurements of viscoelastic materials e.g. magnetic tapes. Using this hardware combination the spread on the measurements is reduced substantially. With this increased accuracy it is now possible to determine the Young's modulus of an actual magnetic coating by measuring the tape and subtracting the basefilm contribution. The justification for this procedure is given and followed by measurements of samples of different origins.