Chemical and mechanical performance of flexible magnetic tape containing chromium dioxide

The development of a magnetic-recording tape using chromium dioxide suitable for use with the tape drive of the IBM 3480 Magnetic Tape Subsystem was found to require careful optimization of the chemical and mechanical properties of the coating. This paper discusses the role of chromium dioxide in the oxidative and hydrolytic degradation of the polyester-polyurethane binders used in most flexible tape coatings, and the subsequent necessity for careful binder selection to eliminate (for all practical purposes) these degradative effects. In addition to the chemical behavior, the paper discusses the role of the interaction of the chromium dioxide with the binder necessary to obtain mechanical performance suitable for the 3480 tape drive. A high modulus and a relatively high glass-transition temperature were found to be required to avoid changes in the frictional properties of the tape. The incorporation of a rough-textured back coat was found to control the change in the surface topography of the recording surface near the spool hub which arises as a result of compressive forces.