Elastic and viscoelastic behavior of a magnetic recording tape

The mechanical behavior of a trilayer Mylar-based magnetic recording tape has been studied by three complementary methods, applied either to the complete tape or to samples prepared by the selective removal of its front or back coatings. One method provided tensile stress-strain and creep data, another exploited the phenomenon of thermal curling, and a third or mandrel method was used to measure relaxation and recovery in simple bending. Despite the large relative thickness of the Mylar substrate, both the initial stiffness and subsequent relaxation behavior of the tape were strongly influenced by the surface magnetic coatings, and particularly by the oriented and calendered frontcoat, which exhibited elastic anisotropy and an enhanced longitudinal Young's modulus of up to five times that of the Mylar core. As a consequence, the magnetically active frontcoat emerged as the most highly stressed component of the tape, and initially supported almost half of an imposed tensile load. The high initial modulus of the oriented and calendered frontcoat was attributed to the reinforcement provided by the magnetic oxide dispersed in the polymeric frontcoat binder. The substantial viscoelastic behavior of the coatings was also linked to their composite structure, and specifically to the ability of the binder to relax the enhanced initial modulus conferred by the presence of the oxide.